Using AES encryption in C

Question

I can t seem to find a nice clean example of using AES 128 bit encryption   Does anyone have some sample code

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Using AES or implementing AES   To use AES  there is the System Security Cryptography RijndaelManaged class

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If you just want to use the built-in crypto provider RijndaelManaged  check out the following help article  it also has a simple code sample       http   msdn microsoft com en-us library system security cryptography rijndaelmanaged aspx   And just in case you need the sample in a hurry  here it is in all its plagiarized glory   using System  using System IO  using System Security Cryptography   namespace RijndaelManaged Example       class RijndaelExample               public static void Main                         try                                string original    Here is some data to encrypt                        Create a new instance of the RijndaelManaged                     class   This generates a new key and initialization                      vector  IV                    using  RijndaelManaged myRijndael   new RijndaelManaged                                           myRijndael GenerateKey                        myRijndael GenerateIV                           Encrypt the string to an array of bytes                       byte   encrypted   EncryptStringToBytes original  myRijndael Key  myRijndael IV                           Decrypt the bytes to a string                       string roundtrip   DecryptStringFromBytes encrypted  myRijndael Key  myRijndael IV                          Display the original data and the decrypted data                      Console WriteLine  Original     0    original                       Console WriteLine  Round Trip   0    roundtrip                                                catch  Exception e                                Console WriteLine  Error   0    e Message                                   static byte   EncryptStringToBytes string plainText  byte   Key  byte   IV                           Check arguments               if  plainText    null    plainText Length  lt   0                  throw new ArgumentNullException  plainText                if  Key    null    Key Length  lt   0                  throw new ArgumentNullException  Key                if  IV    null    IV Length  lt   0                  throw new ArgumentNullException  IV                byte   encrypted                 Create an RijndaelManaged object                 with the specified key and IV               using  RijndaelManaged rijAlg   new RijndaelManaged                                  rijAlg Key   Key                  rijAlg IV   IV                      Create a decryptor to perform the stream transform                  ICryptoTransform encryptor   rijAlg CreateEncryptor rijAlg Key  rijAlg IV                       Create the streams used for encryption                   using  MemoryStream msEncrypt   new MemoryStream                                          using  CryptoStream csEncrypt   new CryptoStream msEncrypt  encryptor  CryptoStreamMode Write                                                 using  StreamWriter swEncrypt   new StreamWriter csEncrypt                                                            Write all data to the stream                              swEncrypt Write plainText                                                     encrypted   msEncrypt ToArray                                                                           Return the encrypted bytes from the memory stream               return encrypted                      static string DecryptStringFromBytes byte   cipherText  byte   Key  byte   IV                           Check arguments               if  cipherText    null    cipherText Length  lt   0                  throw new ArgumentNullException  cipherText                if  Key    null    Key Length  lt   0                  throw new ArgumentNullException  Key                if  IV    null    IV Length  lt   0                  throw new ArgumentNullException  IV                    Declare the string used to hold                 the decrypted text               string plaintext   null                  Create an RijndaelManaged object                 with the specified key and IV               using  RijndaelManaged rijAlg   new RijndaelManaged                                  rijAlg Key   Key                  rijAlg IV   IV                      Create a decrytor to perform the stream transform                  ICryptoTransform decryptor   rijAlg CreateDecryptor rijAlg Key  rijAlg IV                       Create the streams used for decryption                   using  MemoryStream msDecrypt   new MemoryStream cipherText                                         using  CryptoStream csDecrypt   new CryptoStream msDecrypt  decryptor  CryptoStreamMode Read                                                 using  StreamReader srDecrypt   new StreamReader csDecrypt                                                             Read the decrypted bytes from the decrypting stream                                 and place them in a string                              plaintext   srDecrypt ReadToEnd                                                                                                  return plaintext

User · Answer

Using AES or implementing AES   To use AES  there is the System Security Cryptography RijndaelManaged class

User · Answer

I ve recently had to bump up against this again in my own project - and wanted to share the somewhat simpler code that I ve been using  as this question and series of answers kept coming up in my searches   I m not going to get into the security concerns around how often to update things like your Salt and Initialization Vector - that s a topic for a security forum  and there are some great resources out there to look at  This is simply a block of code to implement AesManaged in C    using System  using System IO  using System Security Cryptography  using System Text   namespace Your Namespace Security       public static class Cryptography            region Settings          private static int  iterations   2          private static int  keySize   256           private static string  hash        SHA1           private static string  salt        aselrias38490a32      Random         private static string  vector      8947az34awl34kjq      Random           endregion          public static string Encrypt string value  string password                return Encrypt lt AesManaged gt  value  password                     public static string Encrypt lt T gt  string value  string password                   where T   SymmetricAlgorithm  new                 byte   vectorBytes   GetBytes lt ASCIIEncoding gt   vector               byte   saltBytes   GetBytes lt ASCIIEncoding gt   salt               byte   valueBytes   GetBytes lt UTF8Encoding gt  value                byte   encrypted              using  T cipher   new T                      PasswordDeriveBytes  passwordBytes                        new PasswordDeriveBytes password  saltBytes   hash   iterations                   byte   keyBytes    passwordBytes GetBytes  keySize   8                    cipher Mode   CipherMode CBC                   using  ICryptoTransform encryptor   cipher CreateEncryptor keyBytes  vectorBytes                         using  MemoryStream to   new MemoryStream                              using  CryptoStream writer   new CryptoStream to  encryptor  CryptoStreamMode Write                                 writer Write valueBytes  0  valueBytes Length                               writer FlushFinalBlock                                encrypted   to ToArray                                                                                      cipher Clear                              return Convert ToBase64String encrypted                      public static string Decrypt string value  string password                return Decrypt lt AesManaged gt  value  password                     public static string Decrypt lt T gt  string value  string password  where T   SymmetricAlgorithm  new                 byte   vectorBytes   GetBytes lt ASCIIEncoding gt   vector               byte   saltBytes   GetBytes lt ASCIIEncoding gt   salt               byte   valueBytes   Convert FromBase64String value                byte   decrypted              int decryptedByteCount   0               using  T cipher   new T                      PasswordDeriveBytes  passwordBytes   new PasswordDeriveBytes password  saltBytes   hash   iterations                   byte   keyBytes    passwordBytes GetBytes  keySize   8                    cipher Mode   CipherMode CBC                   try                       using  ICryptoTransform decryptor   cipher CreateDecryptor keyBytes  vectorBytes                             using  MemoryStream from   new MemoryStream valueBytes                                 using  CryptoStream reader   new CryptoStream from  decryptor  CryptoStreamMode Read                                     decrypted   new byte valueBytes Length                                   decryptedByteCount   reader Read decrypted  0  decrypted Length                                                                                                   catch  Exception ex                        return String Empty                                     cipher Clear                              return Encoding UTF8 GetString decrypted  0  decryptedByteCount                        The code is very simple to use  It literally just requires the following   string encrypted   Cryptography Encrypt data   testpass    string decrypted   Cryptography Decrypt encrypted   testpass      By default  the implementation uses AesManaged - but you could actually also insert any other SymmetricAlgorithm  A list of the available SymmetricAlgorithm inheritors for  NET 4 5 can be found at    http   msdn microsoft com en-us library system security cryptography symmetricalgorithm aspx   As of the time of this post  the current list includes     AesManaged RijndaelManaged DESCryptoServiceProvider RC2CryptoServiceProvider  TripleDESCryptoServiceProvider   To use RijndaelManaged with the code above  as an example  you would use   string encrypted   Cryptography Encrypt lt RijndaelManaged gt  dataToEncrypt  password   string decrypted   Cryptography Decrypt lt RijndaelManaged gt  encrypted  password     I hope this is helpful to someone out there

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For a more complete example that performs key derivation in addition to the AES encryption  see the answer and links posted in Getting AES encryption to work across Javascript and C     EDIT a side note  Javascript Cryptography considered harmful  Worth the read

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If you just want to use the built-in crypto provider RijndaelManaged  check out the following help article  it also has a simple code sample       http   msdn microsoft com en-us library system security cryptography rijndaelmanaged aspx   And just in case you need the sample in a hurry  here it is in all its plagiarized glory   using System  using System IO  using System Security Cryptography   namespace RijndaelManaged Example       class RijndaelExample               public static void Main                         try                                string original    Here is some data to encrypt                        Create a new instance of the RijndaelManaged                     class   This generates a new key and initialization                      vector  IV                    using  RijndaelManaged myRijndael   new RijndaelManaged                                           myRijndael GenerateKey                        myRijndael GenerateIV                           Encrypt the string to an array of bytes                       byte   encrypted   EncryptStringToBytes original  myRijndael Key  myRijndael IV                           Decrypt the bytes to a string                       string roundtrip   DecryptStringFromBytes encrypted  myRijndael Key  myRijndael IV                          Display the original data and the decrypted data                      Console WriteLine  Original     0    original                       Console WriteLine  Round Trip   0    roundtrip                                                catch  Exception e                                Console WriteLine  Error   0    e Message                                   static byte   EncryptStringToBytes string plainText  byte   Key  byte   IV                           Check arguments               if  plainText    null    plainText Length  lt   0                  throw new ArgumentNullException  plainText                if  Key    null    Key Length  lt   0                  throw new ArgumentNullException  Key                if  IV    null    IV Length  lt   0                  throw new ArgumentNullException  IV                byte   encrypted                 Create an RijndaelManaged object                 with the specified key and IV               using  RijndaelManaged rijAlg   new RijndaelManaged                                  rijAlg Key   Key                  rijAlg IV   IV                      Create a decryptor to perform the stream transform                  ICryptoTransform encryptor   rijAlg CreateEncryptor rijAlg Key  rijAlg IV                       Create the streams used for encryption                   using  MemoryStream msEncrypt   new MemoryStream                                          using  CryptoStream csEncrypt   new CryptoStream msEncrypt  encryptor  CryptoStreamMode Write                                                 using  StreamWriter swEncrypt   new StreamWriter csEncrypt                                                            Write all data to the stream                              swEncrypt Write plainText                                                     encrypted   msEncrypt ToArray                                                                           Return the encrypted bytes from the memory stream               return encrypted                      static string DecryptStringFromBytes byte   cipherText  byte   Key  byte   IV                           Check arguments               if  cipherText    null    cipherText Length  lt   0                  throw new ArgumentNullException  cipherText                if  Key    null    Key Length  lt   0                  throw new ArgumentNullException  Key                if  IV    null    IV Length  lt   0                  throw new ArgumentNullException  IV                    Declare the string used to hold                 the decrypted text               string plaintext   null                  Create an RijndaelManaged object                 with the specified key and IV               using  RijndaelManaged rijAlg   new RijndaelManaged                                  rijAlg Key   Key                  rijAlg IV   IV                      Create a decrytor to perform the stream transform                  ICryptoTransform decryptor   rijAlg CreateDecryptor rijAlg Key  rijAlg IV                       Create the streams used for decryption                   using  MemoryStream msDecrypt   new MemoryStream cipherText                                         using  CryptoStream csDecrypt   new CryptoStream msDecrypt  decryptor  CryptoStreamMode Read                                                 using  StreamReader srDecrypt   new StreamReader csDecrypt                                                             Read the decrypted bytes from the decrypting stream                                 and place them in a string                              plaintext   srDecrypt ReadToEnd                                                                                                  return plaintext

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Try this code  maybe useful  1 Create New C  Project and add follows code to Form1   using System  using System Windows Forms  using System Security Cryptography   namespace ExampleCrypto       public partial class Form1   Form               public Form1                         InitializeComponent                       private void Form1 Load object sender  EventArgs e                        string strOriginalData   string Empty              string strEncryptedData   string Empty              string strDecryptedData   string Empty               strOriginalData    this is original data 1234567890      your original data in here             MessageBox Show  ORIGINAL DATA  r n    strOriginalData                clsCrypto aes   new clsCrypto                aes IV    this is your IV          your IV             aes KEY    this is your KEY         your KEY                   strEncryptedData   aes Encrypt strOriginalData  CipherMode CBC         your cipher mode             MessageBox Show  ENCRYPTED DATA  r n    strEncryptedData                strDecryptedData   aes Decrypt strEncryptedData  CipherMode CBC               MessageBox Show  DECRYPTED DATA  r n    strDecryptedData                        2 Create clsCrypto cs and copy paste follows code in your class and run your code  I used MD5 to generated Initial Vector IV  and KEY of AES   using System  using System Security Cryptography  using System Text  using System Windows Forms  using System IO  using System Runtime Remoting Metadata W3cXsd2001   namespace ExampleCrypto       public class clsCrypto               private string  KEY   string Empty          protected internal string KEY                       get                               return  KEY                            set                               if   string IsNullOrEmpty value                                          KEY   value                                                     private string  IV   string Empty          protected internal string IV                       get                               return  IV                            set                               if   string IsNullOrEmpty value                                          IV   value                                                     private string CalcMD5 string strInput                        string strOutput   string Empty              if   string IsNullOrEmpty strInput                                 try                                       StringBuilder strHex   new StringBuilder                        using  MD5 md5   MD5 Create                                                  byte   bytArText   Encoding Default GetBytes strInput                           byte   bytArHash   md5 ComputeHash bytArText                           for  int i   0  i  lt  bytArHash Length  i                                                          strHex Append bytArHash i  ToString  X2                                                       strOutput   strHex ToString                                                            catch  Exception ex                                        MessageBox Show ex Message                                               return strOutput                     private byte   GetBytesFromHexString string strInput                        byte   bytArOutput   new byte                    if    string IsNullOrEmpty strInput    amp  amp  strInput Length   2    0                                SoapHexBinary hexBinary   null                  try                                       hexBinary   SoapHexBinary Parse strInput                                     catch  Exception ex                                        MessageBox Show ex Message                                     bytArOutput   hexBinary Value                            return bytArOutput                     private byte   GenerateIV                         byte   bytArOutput   new byte                    try                               string strIV   CalcMD5 IV                   bytArOutput   GetBytesFromHexString strIV                             catch  Exception ex                                MessageBox Show ex Message                             return bytArOutput                     private byte   GenerateKey                         byte   bytArOutput   new byte                    try                               string strKey   CalcMD5 KEY                   bytArOutput   GetBytesFromHexString strKey                             catch  Exception ex                                MessageBox Show ex Message                             return bytArOutput                     protected internal string Encrypt string strInput  CipherMode cipherMode                        string strOutput   string Empty              if   string IsNullOrEmpty strInput                                 try                                       byte   bytePlainText   Encoding Default GetBytes strInput                       using  RijndaelManaged rijManaged   new RijndaelManaged                                                  rijManaged Mode   cipherMode                          rijManaged BlockSize   128                          rijManaged KeySize   128                          rijManaged IV   GenerateIV                            rijManaged Key   GenerateKey                            rijManaged Padding   PaddingMode Zeros                          ICryptoTransform icpoTransform   rijManaged CreateEncryptor rijManaged Key  rijManaged IV                           using  MemoryStream memStream   new MemoryStream                                                          using  CryptoStream cpoStream   new CryptoStream memStream  icpoTransform  CryptoStreamMode Write                                                                 cpoStream Write bytePlainText  0  bytePlainText Length                                   cpoStream FlushFinalBlock                                                              strOutput   Encoding Default GetString memStream ToArray                                                                                       catch  Exception ex                                        MessageBox Show ex Message                                               return strOutput                     protected internal string Decrypt string strInput  CipherMode cipherMode                        string strOutput   string Empty              if   string IsNullOrEmpty strInput                                 try                                       byte   byteCipherText   Encoding Default GetBytes strInput                       byte   byteBuffer   new byte strInput Length                       using  RijndaelManaged rijManaged   new RijndaelManaged                                                  rijManaged Mode   cipherMode                          rijManaged BlockSize   128                          rijManaged KeySize   128                          rijManaged IV   GenerateIV                            rijManaged Key   GenerateKey                            rijManaged Padding   PaddingMode Zeros                          ICryptoTransform icpoTransform   rijManaged CreateDecryptor rijManaged Key  rijManaged IV                           using  MemoryStream memStream   new MemoryStream byteCipherText                                                         using  CryptoStream cpoStream   new CryptoStream memStream  icpoTransform  CryptoStreamMode Read                                                                 cpoStream Read byteBuffer  0  byteBuffer Length                                                             strOutput   Encoding Default GetString byteBuffer                                                                                     catch  Exception ex                                        MessageBox Show ex Message                                               return strOutput

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here is a neat and clean code to understand AES 256 algorithm implemented in C  call Encrypt function as encryptedstring   cryptObj Encrypt username   AGARAMUDHALA    EZHUTHELLAM    SHA1   3    1B2c3D4e5F6g7H8   256    public class Crypt       public string Encrypt string passtext  string passPhrase  string saltV  string hashstring  int Iterations  string initVect  int keysize                string functionReturnValue   null             Convert strings into byte arrays             Let us assume that strings only contain ASCII codes             If strings include Unicode characters  use Unicode  UTF7  or UTF8            encoding          byte   initVectorBytes   null          initVectorBytes   Encoding ASCII GetBytes initVect           byte   saltValueBytes   null          saltValueBytes   Encoding ASCII GetBytes saltV               Convert our plaintext into a byte array             Let us assume that plaintext contains UTF8-encoded characters          byte   plainTextBytes   null          plainTextBytes   Encoding UTF8 GetBytes passtext              First  we must create a password  from which the key will be derived             This password will be generated from the specified passphrase and            salt value  The password will be created using the specified hash            algorithm  Password creation can be done in several iterations          PasswordDeriveBytes password   default PasswordDeriveBytes           password   new PasswordDeriveBytes passPhrase  saltValueBytes  hashstring  Iterations              Use the password to generate pseudo-random bytes for the encryption            key  Specify the size of the key in bytes  instead of bits           byte   keyBytes   null          keyBytes   password GetBytes keysize 8              Create uninitialized Rijndael encryption object          RijndaelManaged symmetricKey   default RijndaelManaged           symmetricKey   new RijndaelManaged                It is reasonable to set encryption mode to Cipher Block Chaining             CBC   Use default options for other symmetric key parameters          symmetricKey Mode   CipherMode CBC             Generate encryptor from the existing key bytes and initialization            vector  Key size will be defined based on the number of the key            bytes          ICryptoTransform encryptor   default ICryptoTransform           encryptor   symmetricKey CreateEncryptor keyBytes  initVectorBytes               Define memory stream which will be used to hold encrypted data          MemoryStream memoryStream   default MemoryStream           memoryStream   new MemoryStream                Define cryptographic stream  always use Write mode for encryption           CryptoStream cryptoStream   default CryptoStream           cryptoStream   new CryptoStream memoryStream  encryptor  CryptoStreamMode Write              Start encrypting          cryptoStream Write plainTextBytes  0  plainTextBytes Length               Finish encrypting          cryptoStream FlushFinalBlock               Convert our encrypted data from a memory stream into a byte array          byte   cipherTextBytes   null          cipherTextBytes   memoryStream ToArray                Close both streams          memoryStream Close            cryptoStream Close                Convert encrypted data into a base64-encoded string          string cipherText   null          cipherText   Convert ToBase64String cipherTextBytes            functionReturnValue   cipherText          return functionReturnValue            public string Decrypt string cipherText  string passPhrase  string saltValue  string hashAlgorithm  int passwordIterations  string initVector  int keySize                string functionReturnValue   null              Convert strings defining encryption key characteristics into byte            arrays  Let us assume that strings only contain ASCII codes             If strings include Unicode characters  use Unicode  UTF7  or UTF8            encoding                byte   initVectorBytes   null              initVectorBytes   Encoding ASCII GetBytes initVector                byte   saltValueBytes   null              saltValueBytes   Encoding ASCII GetBytes saltValue                   Convert our ciphertext into a byte array              byte   cipherTextBytes   null              cipherTextBytes   Convert FromBase64String cipherText                   First  we must create a password  from which the key will be                derived  This password will be generated from the specified                passphrase and salt value  The password will be created using                the specified hash algorithm  Password creation can be done in                several iterations              PasswordDeriveBytes password   default PasswordDeriveBytes               password   new PasswordDeriveBytes passPhrase  saltValueBytes  hashAlgorithm  passwordIterations                   Use the password to generate pseudo-random bytes for the encryption                key  Specify the size of the key in bytes  instead of bits               byte   keyBytes   null              keyBytes   password GetBytes keySize   8                   Create uninitialized Rijndael encryption object              RijndaelManaged symmetricKey   default RijndaelManaged               symmetricKey   new RijndaelManaged                    It is reasonable to set encryption mode to Cipher Block Chaining                 CBC   Use default options for other symmetric key parameters              symmetricKey Mode   CipherMode CBC                  Generate decryptor from the existing key bytes and initialization                vector  Key size will be defined based on the number of the key                bytes              ICryptoTransform decryptor   default ICryptoTransform               decryptor   symmetricKey CreateDecryptor keyBytes  initVectorBytes                   Define memory stream which will be used to hold encrypted data              MemoryStream memoryStream   default MemoryStream               memoryStream   new MemoryStream cipherTextBytes                   Define memory stream which will be used to hold encrypted data              CryptoStream cryptoStream   default CryptoStream               cryptoStream   new CryptoStream memoryStream  decryptor  CryptoStreamMode Read                   Since at this point we don t know what the size of decrypted data                will be  allocate the buffer long enough to hold ciphertext                 plaintext is never longer than ciphertext              byte   plainTextBytes   null              plainTextBytes   new byte cipherTextBytes Length   1                   Start decrypting              int decryptedByteCount   0              decryptedByteCount   cryptoStream Read plainTextBytes  0  plainTextBytes Length                   Close both streams              memoryStream Close                cryptoStream Close                    Convert decrypted data into a string                 Let us assume that the original plaintext string was UTF8-encoded              string plainText   null              plainText   Encoding UTF8 GetString plainTextBytes  0  decryptedByteCount                   Return decrypted string              functionReturnValue   plainText            return functionReturnValue

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Look at sample in here    http   msdn microsoft com en-us library system security cryptography rijndaelmanaged v VS 100  aspx Y2262  The example on MSDN does not run normally  an error occurs  because there is no initial value of Initial Vector iv  and Key  I add 2 line code and now work normally   More details see below   using System Windows Forms  using System  using System Text  using System IO  using System Security Cryptography   namespace AES TESTER      public partial class Form1   Form             public Form1                      InitializeComponent                     private void Form1 Load object sender  EventArgs e                     try                          string original    Here is some data to encrypt                MessageBox Show  Original        original                   Create a new instance of the RijndaelManaged                class   This generates a new key and initialization                 vector  IV               using  RijndaelManaged myRijndael   new RijndaelManaged                                   myRijndael GenerateKey                     myRijndael GenerateIV                        Encrypt the string to an array of bytes                  byte   encrypted   EncryptStringToBytes original  myRijndael Key  myRijndael IV                    StringBuilder s   new StringBuilder                    foreach  byte item in encrypted                                       s Append item ToString  X2                                             MessageBox Show  Encrypted        s                       Decrypt the bytes to a string                  string decrypted   DecryptStringFromBytes encrypted  myRijndael Key  myRijndael IV                      Display the original data and the decrypted data                  MessageBox Show  Decrypted         decrypted                                    catch  Exception ex                        MessageBox Show  Error   0    ex Message                        static byte   EncryptStringToBytes string plainText  byte   Key  byte   IV                   Check arguments          if  plainText    null    plainText Length  lt   0              throw new ArgumentNullException  plainText            if  Key    null    Key Length  lt   0              throw new ArgumentNullException  Key            if  IV    null    IV Length  lt   0              throw new ArgumentNullException  Key            byte   encrypted             Create an RijndaelManaged object            with the specified key and IV          using  RijndaelManaged rijAlg   new RijndaelManaged                          rijAlg Key   Key              rijAlg IV   IV              rijAlg Mode   CipherMode CBC              rijAlg Padding   PaddingMode Zeros                  Create a decrytor to perform the stream transform              ICryptoTransform encryptor   rijAlg CreateEncryptor rijAlg Key  rijAlg IV                   Create the streams used for encryption              using  MemoryStream msEncrypt   new MemoryStream                                  using  CryptoStream csEncrypt   new CryptoStream msEncrypt  encryptor  CryptoStreamMode Write                                         using  StreamWriter swEncrypt   new StreamWriter csEncrypt                                                    Write all data to the stream                          swEncrypt Write plainText                                             encrypted   msEncrypt ToArray                                                           Return the encrypted bytes from the memory stream          return encrypted              static string DecryptStringFromBytes byte   cipherText  byte   Key  byte   IV                   Check arguments          if  cipherText    null    cipherText Length  lt   0              throw new ArgumentNullException  cipherText            if  Key    null    Key Length  lt   0              throw new ArgumentNullException  Key            if  IV    null    IV Length  lt   0              throw new ArgumentNullException  Key                Declare the string used to hold            the decrypted text          string plaintext   null              Create an RijndaelManaged object            with the specified key and IV          using  RijndaelManaged rijAlg   new RijndaelManaged                          rijAlg Key   Key              rijAlg IV   IV              rijAlg Mode   CipherMode CBC              rijAlg Padding   PaddingMode Zeros                  Create a decrytor to perform the stream transform              ICryptoTransform decryptor   rijAlg CreateDecryptor rijAlg Key  rijAlg IV                   Create the streams used for decryption              using  MemoryStream msDecrypt   new MemoryStream cipherText                                 using  CryptoStream csDecrypt   new CryptoStream msDecrypt  decryptor  CryptoStreamMode Read                                         using  StreamReader srDecrypt   new StreamReader csDecrypt                                                     Read the decrypted bytes from the decrypting stream                            and place them in a string                          plaintext   srDecrypt ReadToEnd                                                                              return plaintext

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Look at sample in here    http   msdn microsoft com en-us library system security cryptography rijndaelmanaged v VS 100  aspx Y2262  The example on MSDN does not run normally  an error occurs  because there is no initial value of Initial Vector iv  and Key  I add 2 line code and now work normally   More details see below   using System Windows Forms  using System  using System Text  using System IO  using System Security Cryptography   namespace AES TESTER      public partial class Form1   Form             public Form1                      InitializeComponent                     private void Form1 Load object sender  EventArgs e                     try                          string original    Here is some data to encrypt                MessageBox Show  Original        original                   Create a new instance of the RijndaelManaged                class   This generates a new key and initialization                 vector  IV               using  RijndaelManaged myRijndael   new RijndaelManaged                                   myRijndael GenerateKey                     myRijndael GenerateIV                        Encrypt the string to an array of bytes                  byte   encrypted   EncryptStringToBytes original  myRijndael Key  myRijndael IV                    StringBuilder s   new StringBuilder                    foreach  byte item in encrypted                                       s Append item ToString  X2                                             MessageBox Show  Encrypted        s                       Decrypt the bytes to a string                  string decrypted   DecryptStringFromBytes encrypted  myRijndael Key  myRijndael IV                      Display the original data and the decrypted data                  MessageBox Show  Decrypted         decrypted                                    catch  Exception ex                        MessageBox Show  Error   0    ex Message                        static byte   EncryptStringToBytes string plainText  byte   Key  byte   IV                   Check arguments          if  plainText    null    plainText Length  lt   0              throw new ArgumentNullException  plainText            if  Key    null    Key Length  lt   0              throw new ArgumentNullException  Key            if  IV    null    IV Length  lt   0              throw new ArgumentNullException  Key            byte   encrypted             Create an RijndaelManaged object            with the specified key and IV          using  RijndaelManaged rijAlg   new RijndaelManaged                          rijAlg Key   Key              rijAlg IV   IV              rijAlg Mode   CipherMode CBC              rijAlg Padding   PaddingMode Zeros                  Create a decrytor to perform the stream transform              ICryptoTransform encryptor   rijAlg CreateEncryptor rijAlg Key  rijAlg IV                   Create the streams used for encryption              using  MemoryStream msEncrypt   new MemoryStream                                  using  CryptoStream csEncrypt   new CryptoStream msEncrypt  encryptor  CryptoStreamMode Write                                         using  StreamWriter swEncrypt   new StreamWriter csEncrypt                                                    Write all data to the stream                          swEncrypt Write plainText                                             encrypted   msEncrypt ToArray                                                           Return the encrypted bytes from the memory stream          return encrypted              static string DecryptStringFromBytes byte   cipherText  byte   Key  byte   IV                   Check arguments          if  cipherText    null    cipherText Length  lt   0              throw new ArgumentNullException  cipherText            if  Key    null    Key Length  lt   0              throw new ArgumentNullException  Key            if  IV    null    IV Length  lt   0              throw new ArgumentNullException  Key                Declare the string used to hold            the decrypted text          string plaintext   null              Create an RijndaelManaged object            with the specified key and IV          using  RijndaelManaged rijAlg   new RijndaelManaged                          rijAlg Key   Key              rijAlg IV   IV              rijAlg Mode   CipherMode CBC              rijAlg Padding   PaddingMode Zeros                  Create a decrytor to perform the stream transform              ICryptoTransform decryptor   rijAlg CreateDecryptor rijAlg Key  rijAlg IV                   Create the streams used for decryption              using  MemoryStream msDecrypt   new MemoryStream cipherText                                 using  CryptoStream csDecrypt   new CryptoStream msDecrypt  decryptor  CryptoStreamMode Read                                         using  StreamReader srDecrypt   new StreamReader csDecrypt                                                     Read the decrypted bytes from the decrypting stream                            and place them in a string                          plaintext   srDecrypt ReadToEnd                                                                              return plaintext

User · Answer

For a more complete example that performs key derivation in addition to the AES encryption  see the answer and links posted in Getting AES encryption to work across Javascript and C     EDIT a side note  Javascript Cryptography considered harmful  Worth the read

User · Answer

Using AES or implementing AES   To use AES  there is the System Security Cryptography RijndaelManaged class

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Code to encrypt Data       public byte   encryptdata byte   bytearraytoencrypt  string key  string iv                            AesCryptoServiceProvider dataencrypt   new AesCryptoServiceProvider                   Block size   Gets or sets the block size  in bits  of the cryptographic operation               dataencrypt BlockSize   128                 KeySize  Gets or sets the size  in bits  of the secret key              dataencrypt KeySize   128                 Key  Gets or sets the symmetric key that is used for encryption and decryption               dataencrypt Key   System Text Encoding UTF8 GetBytes key                  IV   Gets or sets the initialization vector  IV  for the symmetric algorithm              dataencrypt IV   System Text Encoding UTF8 GetBytes iv                  Padding  Gets or sets the padding mode used in the symmetric algorithm              dataencrypt Padding   PaddingMode PKCS7                 Mode  Gets or sets the mode for operation of the symmetric algorithm              dataencrypt Mode   CipherMode CBC                 Creates a symmetric AES encryptor object using the current key and initialization vector  IV                ICryptoTransform crypto1   dataencrypt CreateEncryptor dataencrypt Key  dataencrypt IV                  TransformFinalBlock is a special function for transforming the last block or a partial block in the stream                  It returns a new array that contains the remaining transformed bytes  A new array is returned  because the amount of                 information returned at the end might be larger than a single block when padding is added               byte   encrypteddata   crypto1 TransformFinalBlock bytearraytoencrypt  0  bytearraytoencrypt Length                crypto1 Dispose                   return the encrypted data              return encrypteddata                    code to decrypt data     private byte   decryptdata byte   bytearraytodecrypt  string key  string iv                     AesCryptoServiceProvider keydecrypt   new AesCryptoServiceProvider             keydecrypt BlockSize   128           keydecrypt KeySize   128           keydecrypt Key   System Text Encoding UTF8 GetBytes key            keydecrypt IV   System Text Encoding UTF8 GetBytes iv            keydecrypt Padding   PaddingMode PKCS7           keydecrypt Mode   CipherMode CBC           ICryptoTransform crypto1   keydecrypt CreateDecryptor keydecrypt Key  keydecrypt IV             byte   returnbytearray   crypto1 TransformFinalBlock bytearraytodecrypt  0  bytearraytodecrypt Length            crypto1 Dispose             return returnbytearray

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here is a neat and clean code to understand AES 256 algorithm implemented in C  call Encrypt function as encryptedstring   cryptObj Encrypt username   AGARAMUDHALA    EZHUTHELLAM    SHA1   3    1B2c3D4e5F6g7H8   256    public class Crypt       public string Encrypt string passtext  string passPhrase  string saltV  string hashstring  int Iterations  string initVect  int keysize                string functionReturnValue   null             Convert strings into byte arrays             Let us assume that strings only contain ASCII codes             If strings include Unicode characters  use Unicode  UTF7  or UTF8            encoding          byte   initVectorBytes   null          initVectorBytes   Encoding ASCII GetBytes initVect           byte   saltValueBytes   null          saltValueBytes   Encoding ASCII GetBytes saltV               Convert our plaintext into a byte array             Let us assume that plaintext contains UTF8-encoded characters          byte   plainTextBytes   null          plainTextBytes   Encoding UTF8 GetBytes passtext              First  we must create a password  from which the key will be derived             This password will be generated from the specified passphrase and            salt value  The password will be created using the specified hash            algorithm  Password creation can be done in several iterations          PasswordDeriveBytes password   default PasswordDeriveBytes           password   new PasswordDeriveBytes passPhrase  saltValueBytes  hashstring  Iterations              Use the password to generate pseudo-random bytes for the encryption            key  Specify the size of the key in bytes  instead of bits           byte   keyBytes   null          keyBytes   password GetBytes keysize 8              Create uninitialized Rijndael encryption object          RijndaelManaged symmetricKey   default RijndaelManaged           symmetricKey   new RijndaelManaged                It is reasonable to set encryption mode to Cipher Block Chaining             CBC   Use default options for other symmetric key parameters          symmetricKey Mode   CipherMode CBC             Generate encryptor from the existing key bytes and initialization            vector  Key size will be defined based on the number of the key            bytes          ICryptoTransform encryptor   default ICryptoTransform           encryptor   symmetricKey CreateEncryptor keyBytes  initVectorBytes               Define memory stream which will be used to hold encrypted data          MemoryStream memoryStream   default MemoryStream           memoryStream   new MemoryStream                Define cryptographic stream  always use Write mode for encryption           CryptoStream cryptoStream   default CryptoStream           cryptoStream   new CryptoStream memoryStream  encryptor  CryptoStreamMode Write              Start encrypting          cryptoStream Write plainTextBytes  0  plainTextBytes Length               Finish encrypting          cryptoStream FlushFinalBlock               Convert our encrypted data from a memory stream into a byte array          byte   cipherTextBytes   null          cipherTextBytes   memoryStream ToArray                Close both streams          memoryStream Close            cryptoStream Close                Convert encrypted data into a base64-encoded string          string cipherText   null          cipherText   Convert ToBase64String cipherTextBytes            functionReturnValue   cipherText          return functionReturnValue            public string Decrypt string cipherText  string passPhrase  string saltValue  string hashAlgorithm  int passwordIterations  string initVector  int keySize                string functionReturnValue   null              Convert strings defining encryption key characteristics into byte            arrays  Let us assume that strings only contain ASCII codes             If strings include Unicode characters  use Unicode  UTF7  or UTF8            encoding                byte   initVectorBytes   null              initVectorBytes   Encoding ASCII GetBytes initVector                byte   saltValueBytes   null              saltValueBytes   Encoding ASCII GetBytes saltValue                   Convert our ciphertext into a byte array              byte   cipherTextBytes   null              cipherTextBytes   Convert FromBase64String cipherText                   First  we must create a password  from which the key will be                derived  This password will be generated from the specified                passphrase and salt value  The password will be created using                the specified hash algorithm  Password creation can be done in                several iterations              PasswordDeriveBytes password   default PasswordDeriveBytes               password   new PasswordDeriveBytes passPhrase  saltValueBytes  hashAlgorithm  passwordIterations                   Use the password to generate pseudo-random bytes for the encryption                key  Specify the size of the key in bytes  instead of bits               byte   keyBytes   null              keyBytes   password GetBytes keySize   8                   Create uninitialized Rijndael encryption object              RijndaelManaged symmetricKey   default RijndaelManaged               symmetricKey   new RijndaelManaged                    It is reasonable to set encryption mode to Cipher Block Chaining                 CBC   Use default options for other symmetric key parameters              symmetricKey Mode   CipherMode CBC                  Generate decryptor from the existing key bytes and initialization                vector  Key size will be defined based on the number of the key                bytes              ICryptoTransform decryptor   default ICryptoTransform               decryptor   symmetricKey CreateDecryptor keyBytes  initVectorBytes                   Define memory stream which will be used to hold encrypted data              MemoryStream memoryStream   default MemoryStream               memoryStream   new MemoryStream cipherTextBytes                   Define memory stream which will be used to hold encrypted data              CryptoStream cryptoStream   default CryptoStream               cryptoStream   new CryptoStream memoryStream  decryptor  CryptoStreamMode Read                   Since at this point we don t know what the size of decrypted data                will be  allocate the buffer long enough to hold ciphertext                 plaintext is never longer than ciphertext              byte   plainTextBytes   null              plainTextBytes   new byte cipherTextBytes Length   1                   Start decrypting              int decryptedByteCount   0              decryptedByteCount   cryptoStream Read plainTextBytes  0  plainTextBytes Length                   Close both streams              memoryStream Close                cryptoStream Close                    Convert decrypted data into a string                 Let us assume that the original plaintext string was UTF8-encoded              string plainText   null              plainText   Encoding UTF8 GetString plainTextBytes  0  decryptedByteCount                   Return decrypted string              functionReturnValue   plainText            return functionReturnValue

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http   www codeproject com Articles 769741 Csharp-AES-bits-Encryption-Library-with-Salt  using System Security Cryptography  using System IO        public byte   AES Encrypt byte   bytesToBeEncrypted  byte   passwordBytes        byte   encryptedBytes   null      byte   saltBytes   new byte     1  2  3  4  5  6  7  8        using  MemoryStream ms   new MemoryStream                  using  RijndaelManaged AES   new RijndaelManaged                          AES KeySize   256              AES BlockSize   128              var key   new Rfc2898DeriveBytes passwordBytes  saltBytes  1000               AES Key   key GetBytes AES KeySize   8               AES IV   key GetBytes AES BlockSize   8               AES Mode   CipherMode CBC              using  var cs   new CryptoStream ms  AES CreateEncryptor    CryptoStreamMode Write                                 cs Write bytesToBeEncrypted  0  bytesToBeEncrypted Length                   cs Close                              encryptedBytes   ms ToArray                        return encryptedBytes     public byte   AES Decrypt byte   bytesToBeDecrypted  byte   passwordBytes        byte   decryptedBytes   null      byte   saltBytes   new byte     1  2  3  4  5  6  7  8        using  MemoryStream ms   new MemoryStream                  using  RijndaelManaged AES   new RijndaelManaged                          AES KeySize   256              AES BlockSize   128              var key   new Rfc2898DeriveBytes passwordBytes  saltBytes  1000               AES Key   key GetBytes AES KeySize   8               AES IV   key GetBytes AES BlockSize   8               AES Mode   CipherMode CBC              using  var cs   new CryptoStream ms  AES CreateDecryptor    CryptoStreamMode Write                                 cs Write bytesToBeDecrypted  0  bytesToBeDecrypted Length                   cs Close                              decryptedBytes   ms ToArray                        return decryptedBytes

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http   www codeproject com Articles 769741 Csharp-AES-bits-Encryption-Library-with-Salt  using System Security Cryptography  using System IO        public byte   AES Encrypt byte   bytesToBeEncrypted  byte   passwordBytes        byte   encryptedBytes   null      byte   saltBytes   new byte     1  2  3  4  5  6  7  8        using  MemoryStream ms   new MemoryStream                  using  RijndaelManaged AES   new RijndaelManaged                          AES KeySize   256              AES BlockSize   128              var key   new Rfc2898DeriveBytes passwordBytes  saltBytes  1000               AES Key   key GetBytes AES KeySize   8               AES IV   key GetBytes AES BlockSize   8               AES Mode   CipherMode CBC              using  var cs   new CryptoStream ms  AES CreateEncryptor    CryptoStreamMode Write                                 cs Write bytesToBeEncrypted  0  bytesToBeEncrypted Length                   cs Close                              encryptedBytes   ms ToArray                        return encryptedBytes     public byte   AES Decrypt byte   bytesToBeDecrypted  byte   passwordBytes        byte   decryptedBytes   null      byte   saltBytes   new byte     1  2  3  4  5  6  7  8        using  MemoryStream ms   new MemoryStream                  using  RijndaelManaged AES   new RijndaelManaged                          AES KeySize   256              AES BlockSize   128              var key   new Rfc2898DeriveBytes passwordBytes  saltBytes  1000               AES Key   key GetBytes AES KeySize   8               AES IV   key GetBytes AES BlockSize   8               AES Mode   CipherMode CBC              using  var cs   new CryptoStream ms  AES CreateDecryptor    CryptoStreamMode Write                                 cs Write bytesToBeDecrypted  0  bytesToBeDecrypted Length                   cs Close                              decryptedBytes   ms ToArray                        return decryptedBytes

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You can use password from text box like key    With this code you can encrypt decrypt text  picture  word document  pdf        public class Rijndael       private byte   key      private readonly byte   vector     255  64  191  111  23  3  113  119  231  121  252  112  79  32  114  156         ICryptoTransform EnkValue  DekValue       public Rijndael byte   key                this key   key          RijndaelManaged rm   new RijndaelManaged            rm Padding   PaddingMode PKCS7          EnkValue   rm CreateEncryptor key  vector           DekValue   rm CreateDecryptor key  vector              public byte   Encrypt byte   byte                 byte   enkByte  byte          byte   enkNewByte          using  MemoryStream ms   new MemoryStream                          using  CryptoStream cs   new CryptoStream ms  EnkValue  CryptoStreamMode Write                                 cs Write enkByte  0  enkByte Length                   cs FlushFinalBlock                     ms Position   0                  enkNewByte  new byte ms Length                   ms Read enkNewByte  0  enkNewByte Length                                   return enkNeyByte             public byte   Dekrypt byte   enkByte                byte   dekByte          using  MemoryStream ms   new MemoryStream                          using  CryptoStream cs   new CryptoStream ms  DekValue  CryptoStreamMode Write                                 cs Write enkByte  0  enkByte Length                   cs FlushFinalBlock                     ms Position   0                  dekByte  new byte ms Length                   ms Read dekByte  0  dekByte Length                                   return dekByte            Convert password from text box to byte array     private byte   ConvertPasswordToByte string password                byte   key   new byte 32           for  int i   0  i  lt  passwprd Length  i                          key i    Convert ToByte passwprd i                      return key

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Code to encrypt Data       public byte   encryptdata byte   bytearraytoencrypt  string key  string iv                            AesCryptoServiceProvider dataencrypt   new AesCryptoServiceProvider                   Block size   Gets or sets the block size  in bits  of the cryptographic operation               dataencrypt BlockSize   128                 KeySize  Gets or sets the size  in bits  of the secret key              dataencrypt KeySize   128                 Key  Gets or sets the symmetric key that is used for encryption and decryption               dataencrypt Key   System Text Encoding UTF8 GetBytes key                  IV   Gets or sets the initialization vector  IV  for the symmetric algorithm              dataencrypt IV   System Text Encoding UTF8 GetBytes iv                  Padding  Gets or sets the padding mode used in the symmetric algorithm              dataencrypt Padding   PaddingMode PKCS7                 Mode  Gets or sets the mode for operation of the symmetric algorithm              dataencrypt Mode   CipherMode CBC                 Creates a symmetric AES encryptor object using the current key and initialization vector  IV                ICryptoTransform crypto1   dataencrypt CreateEncryptor dataencrypt Key  dataencrypt IV                  TransformFinalBlock is a special function for transforming the last block or a partial block in the stream                  It returns a new array that contains the remaining transformed bytes  A new array is returned  because the amount of                 information returned at the end might be larger than a single block when padding is added               byte   encrypteddata   crypto1 TransformFinalBlock bytearraytoencrypt  0  bytearraytoencrypt Length                crypto1 Dispose                   return the encrypted data              return encrypteddata                    code to decrypt data     private byte   decryptdata byte   bytearraytodecrypt  string key  string iv                     AesCryptoServiceProvider keydecrypt   new AesCryptoServiceProvider             keydecrypt BlockSize   128           keydecrypt KeySize   128           keydecrypt Key   System Text Encoding UTF8 GetBytes key            keydecrypt IV   System Text Encoding UTF8 GetBytes iv            keydecrypt Padding   PaddingMode PKCS7           keydecrypt Mode   CipherMode CBC           ICryptoTransform crypto1   keydecrypt CreateDecryptor keydecrypt Key  keydecrypt IV             byte   returnbytearray   crypto1 TransformFinalBlock bytearraytodecrypt  0  bytearraytodecrypt Length            crypto1 Dispose             return returnbytearray

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You can use password from text box like key    With this code you can encrypt decrypt text  picture  word document  pdf        public class Rijndael       private byte   key      private readonly byte   vector     255  64  191  111  23  3  113  119  231  121  252  112  79  32  114  156         ICryptoTransform EnkValue  DekValue       public Rijndael byte   key                this key   key          RijndaelManaged rm   new RijndaelManaged            rm Padding   PaddingMode PKCS7          EnkValue   rm CreateEncryptor key  vector           DekValue   rm CreateDecryptor key  vector              public byte   Encrypt byte   byte                 byte   enkByte  byte          byte   enkNewByte          using  MemoryStream ms   new MemoryStream                          using  CryptoStream cs   new CryptoStream ms  EnkValue  CryptoStreamMode Write                                 cs Write enkByte  0  enkByte Length                   cs FlushFinalBlock                     ms Position   0                  enkNewByte  new byte ms Length                   ms Read enkNewByte  0  enkNewByte Length                                   return enkNeyByte             public byte   Dekrypt byte   enkByte                byte   dekByte          using  MemoryStream ms   new MemoryStream                          using  CryptoStream cs   new CryptoStream ms  DekValue  CryptoStreamMode Write                                 cs Write enkByte  0  enkByte Length                   cs FlushFinalBlock                     ms Position   0                  dekByte  new byte ms Length                   ms Read dekByte  0  dekByte Length                                   return dekByte            Convert password from text box to byte array     private byte   ConvertPasswordToByte string password                byte   key   new byte 32           for  int i   0  i  lt  passwprd Length  i                          key i    Convert ToByte passwprd i                      return key

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If you just want to use the built-in crypto provider RijndaelManaged  check out the following help article  it also has a simple code sample       http   msdn microsoft com en-us library system security cryptography rijndaelmanaged aspx   And just in case you need the sample in a hurry  here it is in all its plagiarized glory   using System  using System IO  using System Security Cryptography   namespace RijndaelManaged Example       class RijndaelExample               public static void Main                         try                                string original    Here is some data to encrypt                        Create a new instance of the RijndaelManaged                     class   This generates a new key and initialization                      vector  IV                    using  RijndaelManaged myRijndael   new RijndaelManaged                                           myRijndael GenerateKey                        myRijndael GenerateIV                           Encrypt the string to an array of bytes                       byte   encrypted   EncryptStringToBytes original  myRijndael Key  myRijndael IV                           Decrypt the bytes to a string                       string roundtrip   DecryptStringFromBytes encrypted  myRijndael Key  myRijndael IV                          Display the original data and the decrypted data                      Console WriteLine  Original     0    original                       Console WriteLine  Round Trip   0    roundtrip                                                catch  Exception e                                Console WriteLine  Error   0    e Message                                   static byte   EncryptStringToBytes string plainText  byte   Key  byte   IV                           Check arguments               if  plainText    null    plainText Length  lt   0                  throw new ArgumentNullException  plainText                if  Key    null    Key Length  lt   0                  throw new ArgumentNullException  Key                if  IV    null    IV Length  lt   0                  throw new ArgumentNullException  IV                byte   encrypted                 Create an RijndaelManaged object                 with the specified key and IV               using  RijndaelManaged rijAlg   new RijndaelManaged                                  rijAlg Key   Key                  rijAlg IV   IV                      Create a decryptor to perform the stream transform                  ICryptoTransform encryptor   rijAlg CreateEncryptor rijAlg Key  rijAlg IV                       Create the streams used for encryption                   using  MemoryStream msEncrypt   new MemoryStream                                          using  CryptoStream csEncrypt   new CryptoStream msEncrypt  encryptor  CryptoStreamMode Write                                                 using  StreamWriter swEncrypt   new StreamWriter csEncrypt                                                            Write all data to the stream                              swEncrypt Write plainText                                                     encrypted   msEncrypt ToArray                                                                           Return the encrypted bytes from the memory stream               return encrypted                      static string DecryptStringFromBytes byte   cipherText  byte   Key  byte   IV                           Check arguments               if  cipherText    null    cipherText Length  lt   0                  throw new ArgumentNullException  cipherText                if  Key    null    Key Length  lt   0                  throw new ArgumentNullException  Key                if  IV    null    IV Length  lt   0                  throw new ArgumentNullException  IV                    Declare the string used to hold                 the decrypted text               string plaintext   null                  Create an RijndaelManaged object                 with the specified key and IV               using  RijndaelManaged rijAlg   new RijndaelManaged                                  rijAlg Key   Key                  rijAlg IV   IV                      Create a decrytor to perform the stream transform                  ICryptoTransform decryptor   rijAlg CreateDecryptor rijAlg Key  rijAlg IV                       Create the streams used for decryption                   using  MemoryStream msDecrypt   new MemoryStream cipherText                                         using  CryptoStream csDecrypt   new CryptoStream msDecrypt  decryptor  CryptoStreamMode Read                                                 using  StreamReader srDecrypt   new StreamReader csDecrypt                                                             Read the decrypted bytes from the decrypting stream                                 and place them in a string                              plaintext   srDecrypt ReadToEnd                                                                                                  return plaintext

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If you just want to use the built-in crypto provider RijndaelManaged  check out the following help article  it also has a simple code sample       http   msdn microsoft com en-us library system security cryptography rijndaelmanaged aspx   And just in case you need the sample in a hurry  here it is in all its plagiarized glory   using System  using System IO  using System Security Cryptography   namespace RijndaelManaged Example       class RijndaelExample               public static void Main                         try                                string original    Here is some data to encrypt                        Create a new instance of the RijndaelManaged                     class   This generates a new key and initialization                      vector  IV                    using  RijndaelManaged myRijndael   new RijndaelManaged                                           myRijndael GenerateKey                        myRijndael GenerateIV                           Encrypt the string to an array of bytes                       byte   encrypted   EncryptStringToBytes original  myRijndael Key  myRijndael IV                           Decrypt the bytes to a string                       string roundtrip   DecryptStringFromBytes encrypted  myRijndael Key  myRijndael IV                          Display the original data and the decrypted data                      Console WriteLine  Original     0    original                       Console WriteLine  Round Trip   0    roundtrip                                                catch  Exception e                                Console WriteLine  Error   0    e Message                                   static byte   EncryptStringToBytes string plainText  byte   Key  byte   IV                           Check arguments               if  plainText    null    plainText Length  lt   0                  throw new ArgumentNullException  plainText                if  Key    null    Key Length  lt   0                  throw new ArgumentNullException  Key                if  IV    null    IV Length  lt   0                  throw new ArgumentNullException  IV                byte   encrypted                 Create an RijndaelManaged object                 with the specified key and IV               using  RijndaelManaged rijAlg   new RijndaelManaged                                  rijAlg Key   Key                  rijAlg IV   IV                      Create a decryptor to perform the stream transform                  ICryptoTransform encryptor   rijAlg CreateEncryptor rijAlg Key  rijAlg IV                       Create the streams used for encryption                   using  MemoryStream msEncrypt   new MemoryStream                                          using  CryptoStream csEncrypt   new CryptoStream msEncrypt  encryptor  CryptoStreamMode Write                                                 using  StreamWriter swEncrypt   new StreamWriter csEncrypt                                                            Write all data to the stream                              swEncrypt Write plainText                                                     encrypted   msEncrypt ToArray                                                                           Return the encrypted bytes from the memory stream               return encrypted                      static string DecryptStringFromBytes byte   cipherText  byte   Key  byte   IV                           Check arguments               if  cipherText    null    cipherText Length  lt   0                  throw new ArgumentNullException  cipherText                if  Key    null    Key Length  lt   0                  throw new ArgumentNullException  Key                if  IV    null    IV Length  lt   0                  throw new ArgumentNullException  IV                    Declare the string used to hold                 the decrypted text               string plaintext   null                  Create an RijndaelManaged object                 with the specified key and IV               using  RijndaelManaged rijAlg   new RijndaelManaged                                  rijAlg Key   Key                  rijAlg IV   IV                      Create a decrytor to perform the stream transform                  ICryptoTransform decryptor   rijAlg CreateDecryptor rijAlg Key  rijAlg IV                       Create the streams used for decryption                   using  MemoryStream msDecrypt   new MemoryStream cipherText                                         using  CryptoStream csDecrypt   new CryptoStream msDecrypt  decryptor  CryptoStreamMode Read                                                 using  StreamReader srDecrypt   new StreamReader csDecrypt                                                             Read the decrypted bytes from the decrypting stream                                 and place them in a string                              plaintext   srDecrypt ReadToEnd                                                                                                  return plaintext

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Try this code  maybe useful  1 Create New C  Project and add follows code to Form1   using System  using System Windows Forms  using System Security Cryptography   namespace ExampleCrypto       public partial class Form1   Form               public Form1                         InitializeComponent                       private void Form1 Load object sender  EventArgs e                        string strOriginalData   string Empty              string strEncryptedData   string Empty              string strDecryptedData   string Empty               strOriginalData    this is original data 1234567890      your original data in here             MessageBox Show  ORIGINAL DATA  r n    strOriginalData                clsCrypto aes   new clsCrypto                aes IV    this is your IV          your IV             aes KEY    this is your KEY         your KEY                   strEncryptedData   aes Encrypt strOriginalData  CipherMode CBC         your cipher mode             MessageBox Show  ENCRYPTED DATA  r n    strEncryptedData                strDecryptedData   aes Decrypt strEncryptedData  CipherMode CBC               MessageBox Show  DECRYPTED DATA  r n    strDecryptedData                        2 Create clsCrypto cs and copy paste follows code in your class and run your code  I used MD5 to generated Initial Vector IV  and KEY of AES   using System  using System Security Cryptography  using System Text  using System Windows Forms  using System IO  using System Runtime Remoting Metadata W3cXsd2001   namespace ExampleCrypto       public class clsCrypto               private string  KEY   string Empty          protected internal string KEY                       get                               return  KEY                            set                               if   string IsNullOrEmpty value                                          KEY   value                                                     private string  IV   string Empty          protected internal string IV                       get                               return  IV                            set                               if   string IsNullOrEmpty value                                          IV   value                                                     private string CalcMD5 string strInput                        string strOutput   string Empty              if   string IsNullOrEmpty strInput                                 try                                       StringBuilder strHex   new StringBuilder                        using  MD5 md5   MD5 Create                                                  byte   bytArText   Encoding Default GetBytes strInput                           byte   bytArHash   md5 ComputeHash bytArText                           for  int i   0  i  lt  bytArHash Length  i                                                          strHex Append bytArHash i  ToString  X2                                                       strOutput   strHex ToString                                                            catch  Exception ex                                        MessageBox Show ex Message                                               return strOutput                     private byte   GetBytesFromHexString string strInput                        byte   bytArOutput   new byte                    if    string IsNullOrEmpty strInput    amp  amp  strInput Length   2    0                                SoapHexBinary hexBinary   null                  try                                       hexBinary   SoapHexBinary Parse strInput                                     catch  Exception ex                                        MessageBox Show ex Message                                     bytArOutput   hexBinary Value                            return bytArOutput                     private byte   GenerateIV                         byte   bytArOutput   new byte                    try                               string strIV   CalcMD5 IV                   bytArOutput   GetBytesFromHexString strIV                             catch  Exception ex                                MessageBox Show ex Message                             return bytArOutput                     private byte   GenerateKey                         byte   bytArOutput   new byte                    try                               string strKey   CalcMD5 KEY                   bytArOutput   GetBytesFromHexString strKey                             catch  Exception ex                                MessageBox Show ex Message                             return bytArOutput                     protected internal string Encrypt string strInput  CipherMode cipherMode                        string strOutput   string Empty              if   string IsNullOrEmpty strInput                                 try                                       byte   bytePlainText   Encoding Default GetBytes strInput                       using  RijndaelManaged rijManaged   new RijndaelManaged                                                  rijManaged Mode   cipherMode                          rijManaged BlockSize   128                          rijManaged KeySize   128                          rijManaged IV   GenerateIV                            rijManaged Key   GenerateKey                            rijManaged Padding   PaddingMode Zeros                          ICryptoTransform icpoTransform   rijManaged CreateEncryptor rijManaged Key  rijManaged IV                           using  MemoryStream memStream   new MemoryStream                                                          using  CryptoStream cpoStream   new CryptoStream memStream  icpoTransform  CryptoStreamMode Write                                                                 cpoStream Write bytePlainText  0  bytePlainText Length                                   cpoStream FlushFinalBlock                                                              strOutput   Encoding Default GetString memStream ToArray                                                                                       catch  Exception ex                                        MessageBox Show ex Message                                               return strOutput                     protected internal string Decrypt string strInput  CipherMode cipherMode                        string strOutput   string Empty              if   string IsNullOrEmpty strInput                                 try                                       byte   byteCipherText   Encoding Default GetBytes strInput                       byte   byteBuffer   new byte strInput Length                       using  RijndaelManaged rijManaged   new RijndaelManaged                                                  rijManaged Mode   cipherMode                          rijManaged BlockSize   128                          rijManaged KeySize   128                          rijManaged IV   GenerateIV                            rijManaged Key   GenerateKey                            rijManaged Padding   PaddingMode Zeros                          ICryptoTransform icpoTransform   rijManaged CreateDecryptor rijManaged Key  rijManaged IV                           using  MemoryStream memStream   new MemoryStream byteCipherText                                                         using  CryptoStream cpoStream   new CryptoStream memStream  icpoTransform  CryptoStreamMode Read                                                                 cpoStream Read byteBuffer  0  byteBuffer Length                                                             strOutput   Encoding Default GetString byteBuffer                                                                                     catch  Exception ex                                        MessageBox Show ex Message                                               return strOutput

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Using AES or implementing AES   To use AES  there is the System Security Cryptography RijndaelManaged class

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I ve recently had to bump up against this again in my own project - and wanted to share the somewhat simpler code that I ve been using  as this question and series of answers kept coming up in my searches   I m not going to get into the security concerns around how often to update things like your Salt and Initialization Vector - that s a topic for a security forum  and there are some great resources out there to look at  This is simply a block of code to implement AesManaged in C    using System  using System IO  using System Security Cryptography  using System Text   namespace Your Namespace Security       public static class Cryptography            region Settings          private static int  iterations   2          private static int  keySize   256           private static string  hash        SHA1           private static string  salt        aselrias38490a32      Random         private static string  vector      8947az34awl34kjq      Random           endregion          public static string Encrypt string value  string password                return Encrypt lt AesManaged gt  value  password                     public static string Encrypt lt T gt  string value  string password                   where T   SymmetricAlgorithm  new                 byte   vectorBytes   GetBytes lt ASCIIEncoding gt   vector               byte   saltBytes   GetBytes lt ASCIIEncoding gt   salt               byte   valueBytes   GetBytes lt UTF8Encoding gt  value                byte   encrypted              using  T cipher   new T                      PasswordDeriveBytes  passwordBytes                        new PasswordDeriveBytes password  saltBytes   hash   iterations                   byte   keyBytes    passwordBytes GetBytes  keySize   8                    cipher Mode   CipherMode CBC                   using  ICryptoTransform encryptor   cipher CreateEncryptor keyBytes  vectorBytes                         using  MemoryStream to   new MemoryStream                              using  CryptoStream writer   new CryptoStream to  encryptor  CryptoStreamMode Write                                 writer Write valueBytes  0  valueBytes Length                               writer FlushFinalBlock                                encrypted   to ToArray                                                                                      cipher Clear                              return Convert ToBase64String encrypted                      public static string Decrypt string value  string password                return Decrypt lt AesManaged gt  value  password                     public static string Decrypt lt T gt  string value  string password  where T   SymmetricAlgorithm  new                 byte   vectorBytes   GetBytes lt ASCIIEncoding gt   vector               byte   saltBytes   GetBytes lt ASCIIEncoding gt   salt               byte   valueBytes   Convert FromBase64String value                byte   decrypted              int decryptedByteCount   0               using  T cipher   new T                      PasswordDeriveBytes  passwordBytes   new PasswordDeriveBytes password  saltBytes   hash   iterations                   byte   keyBytes    passwordBytes GetBytes  keySize   8                    cipher Mode   CipherMode CBC                   try                       using  ICryptoTransform decryptor   cipher CreateDecryptor keyBytes  vectorBytes                             using  MemoryStream from   new MemoryStream valueBytes                                 using  CryptoStream reader   new CryptoStream from  decryptor  CryptoStreamMode Read                                     decrypted   new byte valueBytes Length                                   decryptedByteCount   reader Read decrypted  0  decrypted Length                                                                                                   catch  Exception ex                        return String Empty                                     cipher Clear                              return Encoding UTF8 GetString decrypted  0  decryptedByteCount                        The code is very simple to use  It literally just requires the following   string encrypted   Cryptography Encrypt data   testpass    string decrypted   Cryptography Decrypt encrypted   testpass      By default  the implementation uses AesManaged - but you could actually also insert any other SymmetricAlgorithm  A list of the available SymmetricAlgorithm inheritors for  NET 4 5 can be found at    http   msdn microsoft com en-us library system security cryptography symmetricalgorithm aspx   As of the time of this post  the current list includes     AesManaged RijndaelManaged DESCryptoServiceProvider RC2CryptoServiceProvider  TripleDESCryptoServiceProvider   To use RijndaelManaged with the code above  as an example  you would use   string encrypted   Cryptography Encrypt lt RijndaelManaged gt  dataToEncrypt  password   string decrypted   Cryptography Decrypt lt RijndaelManaged gt  encrypted  password     I hope this is helpful to someone out there

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