C Example of AES256 encryption using System Security Cryptography Aes

Question

I need to implement AES 256 encryption  decryption and I haven t been able to find an example that works correctly   MSDN suggests that I should use the AES class      The Rijndael class is the predecessor of the Aes algorithm  You should use the Aes algorithm instead of Rijndael  For more information  see the entry The Differences Between Rijndael and AES in the  NET Security blog    Could anyone point me in the direction of a good example using the AES class for AES256   To add a little more clarity   I have a cipher file that contains the shared key and a string of encrypted text  I need to decrypt the text and then validate it   All the examples I ve seen expect at least 2 parameters to perform the encryption decryption    Should I be able to infer the Initialisation vector and the key from the text in the cipher file   This is an example of the text held in my cipher file                  r                 DWn              L

User · Accepted Answer

Once I d discovered all the information of how my client was handling the encryption decryption at their end it was straight forward using the AesManaged example suggested by dtb   The finally implemented code started like this       try                  Create a new instance of the AesManaged class   This generates a new key and initialization vector  IV           AesManaged myAes   new AesManaged                Override the cipher mode  key and IV         myAes Mode   CipherMode ECB          myAes IV   new byte 16    0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0       CRB mode uses an empty IV         myAes Key   CipherKey      Byte array representing the key         myAes Padding   PaddingMode None              Create a encryption object to perform the stream transform          ICryptoTransform encryptor   myAes CreateEncryptor                TODO  perform the encryption   decryption as required               catch  Exception ex                   TODO  Log the error          throw ex

User · Answer

public class AesCryptoService       private static byte   Key   Encoding ASCII GetBytes   quot qwr   h h amp   50 ja9  dcmh3 uw lt  amp    quot        private static byte   IV   Encoding ASCII GetBytes   quot 9   V  A lY amp  t2b quot          public static string EncryptStringToBytes Aes string plainText                if  plainText    null    plainText Length  lt   0              throw new ArgumentNullException  quot plainText quot            if  Key    null    Key Length  lt   0              throw new ArgumentNullException  quot Key quot            if  IV    null    IV Length  lt   0              throw new ArgumentNullException  quot IV quot            byte   encrypted            using  AesCryptoServiceProvider aesAlg   new AesCryptoServiceProvider                          aesAlg Key   Key              aesAlg IV   IV              aesAlg Mode   CipherMode CBC              aesAlg Padding   PaddingMode PKCS7               ICryptoTransform encryptor   aesAlg CreateEncryptor aesAlg Key  aesAlg IV                using  MemoryStream msEncrypt   new MemoryStream                                  using  CryptoStream csEncrypt   new CryptoStream msEncrypt  encryptor  CryptoStreamMode Write                                         using  StreamWriter swEncrypt   new StreamWriter csEncrypt                                                 swEncrypt Write plainText                                             encrypted   msEncrypt ToArray                                                               return Convert ToBase64String encrypted                    public static string DecryptStringFromBytes Aes string Text                if  Text    null    Text Length  lt   0              throw new ArgumentNullException  quot cipherText quot            if  Key    null    Key Length  lt   0              throw new ArgumentNullException  quot Key quot            if  IV    null    IV Length  lt   0              throw new ArgumentNullException  quot IV quot             string plaintext   null          byte   cipherText   Convert FromBase64String Text Replace                      using  AesCryptoServiceProvider aesAlg   new AesCryptoServiceProvider                          aesAlg Key   Key              aesAlg IV   IV              aesAlg Mode   CipherMode CBC              aesAlg Padding   PaddingMode PKCS7                ICryptoTransform decryptor   aesAlg CreateDecryptor aesAlg Key  aesAlg IV                using  MemoryStream msDecrypt   new MemoryStream cipherText                                 using  CryptoStream csDecrypt   new CryptoStream msDecrypt  decryptor  CryptoStreamMode Read                                         using  StreamReader srDecrypt   new StreamReader csDecrypt                                                 plaintext   srDecrypt ReadToEnd                                                                              return plaintext

User · Answer

Maybe this example listed here can help you out  Statement from the author  about 24 lines of code to encrypt  23 to decrypt  Due to the fact that the link in the original posting is dead - here the needed code parts  c amp p without any change to the original source         Copyright  c  2010  lt a href  quot http   www gutgames com quot  gt James Craig lt  a gt       Permission is hereby granted  free of charge  to any person obtaining a copy   of this software and associated documentation files  the  quot Software quot    to deal   in the Software without restriction  including without limitation the rights   to use  copy  modify  merge  publish  distribute  sublicense  and or sell   copies of the Software  and to permit persons to whom the Software is   furnished to do so  subject to the following conditions       The above copyright notice and this permission notice shall be included in   all copies or substantial portions of the Software       THE SOFTWARE IS PROVIDED  quot AS IS quot   WITHOUT WARRANTY OF ANY KIND  EXPRESS OR   IMPLIED  INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT  IN NO EVENT SHALL THE   AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM  DAMAGES OR OTHER   LIABILITY  WHETHER IN AN ACTION OF CONTRACT  TORT OR OTHERWISE  ARISING FROM    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN   THE SOFTWARE           region Usings   using System    using System IO    using System Security Cryptography    using System Text     endregion       namespace Utilities Encryption                lt summary gt            Utility class that handles encryption            lt  summary gt        public static class AESEncryption                    region Static Functions                    lt summary gt                Encrypts a string                lt  summary gt                 lt param name  quot PlainText quot  gt Text to be encrypted lt  param gt                 lt param name  quot Password quot  gt Password to encrypt with lt  param gt                 lt param name  quot Salt quot  gt Salt to encrypt with lt  param gt                 lt param name  quot HashAlgorithm quot  gt Can be either SHA1 or MD5 lt  param gt                 lt param name  quot PasswordIterations quot  gt Number of iterations to do lt  param gt                 lt param name  quot InitialVector quot  gt Needs to be 16 ASCII characters long lt  param gt                 lt param name  quot KeySize quot  gt Can be 128  192  or 256 lt  param gt                 lt returns gt An encrypted string lt  returns gt            public static string Encrypt string PlainText  string Password                string Salt    quot Kosher quot   string HashAlgorithm    quot SHA1 quot                 int PasswordIterations   2  string InitialVector    quot OFRna73m aze01xY quot                 int KeySize   256                            if  string IsNullOrEmpty PlainText                     return  quot  quot                 byte   InitialVectorBytes   Encoding ASCII GetBytes InitialVector                 byte   SaltValueBytes   Encoding ASCII GetBytes Salt                 byte   PlainTextBytes   Encoding UTF8 GetBytes PlainText                 PasswordDeriveBytes DerivedPassword   new PasswordDeriveBytes Password  SaltValueBytes  HashAlgorithm  PasswordIterations                 byte   KeyBytes   DerivedPassword GetBytes KeySize   8                 RijndaelManaged SymmetricKey   new RijndaelManaged                  SymmetricKey Mode   CipherMode CBC                byte   CipherTextBytes   null                using  ICryptoTransform Encryptor   SymmetricKey CreateEncryptor KeyBytes  InitialVectorBytes                                     using  MemoryStream MemStream   new MemoryStream                                              using  CryptoStream CryptoStream   new CryptoStream MemStream  Encryptor  CryptoStreamMode Write                                                     CryptoStream Write PlainTextBytes  0  PlainTextBytes Length                             CryptoStream FlushFinalBlock                              CipherTextBytes   MemStream ToArray                              MemStream Close                              CryptoStream Close                                                                              SymmetricKey Clear                  return Convert ToBase64String CipherTextBytes                                  lt summary gt                Decrypts a string                lt  summary gt                 lt param name  quot CipherText quot  gt Text to be decrypted lt  param gt                 lt param name  quot Password quot  gt Password to decrypt with lt  param gt                 lt param name  quot Salt quot  gt Salt to decrypt with lt  param gt                 lt param name  quot HashAlgorithm quot  gt Can be either SHA1 or MD5 lt  param gt                 lt param name  quot PasswordIterations quot  gt Number of iterations to do lt  param gt                 lt param name  quot InitialVector quot  gt Needs to be 16 ASCII characters long lt  param gt                 lt param name  quot KeySize quot  gt Can be 128  192  or 256 lt  param gt                 lt returns gt A decrypted string lt  returns gt            public static string Decrypt string CipherText  string Password                string Salt    quot Kosher quot   string HashAlgorithm    quot SHA1 quot                 int PasswordIterations   2  string InitialVector    quot OFRna73m aze01xY quot                 int KeySize   256                            if  string IsNullOrEmpty CipherText                     return  quot  quot                 byte   InitialVectorBytes   Encoding ASCII GetBytes InitialVector                 byte   SaltValueBytes   Encoding ASCII GetBytes Salt                 byte   CipherTextBytes   Convert FromBase64String CipherText                 PasswordDeriveBytes DerivedPassword   new PasswordDeriveBytes Password  SaltValueBytes  HashAlgorithm  PasswordIterations                 byte   KeyBytes   DerivedPassword GetBytes KeySize   8                 RijndaelManaged SymmetricKey   new RijndaelManaged                  SymmetricKey Mode   CipherMode CBC                byte   PlainTextBytes   new byte CipherTextBytes Length                 int ByteCount   0                using  ICryptoTransform Decryptor   SymmetricKey CreateDecryptor KeyBytes  InitialVectorBytes                                     using  MemoryStream MemStream   new MemoryStream CipherTextBytes                                             using  CryptoStream CryptoStream   new CryptoStream MemStream  Decryptor  CryptoStreamMode Read                                                         ByteCount   CryptoStream Read PlainTextBytes  0  PlainTextBytes Length                             MemStream Close                              CryptoStream Close                                                                              SymmetricKey Clear                  return Encoding UTF8 GetString PlainTextBytes  0  ByteCount                              endregion

[c#] C# Example of AES256 encryption using System.Security.Cryptography.Aes

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