Encrypting Decrypting a String in C

Question

What is the most modern  best  way of satisfying the following in C    string encryptedString   SomeStaticClass Encrypt sourceString    string decryptedString   SomeStaticClass Decrypt encryptedString     BUT with a minimum of fuss involving salts  keys  mucking about with byte    etc   Been Googling and confused at what I m finding  you can see the list of similar SO Qs to see this is a deceptive question to ask

User · Answer

The easiest way that I ve seen to do encryption is through RSA  Check out the MSDN on it  http   msdn microsoft com en-us library system security cryptography rsacryptoserviceprovider aspx  It does involve using bytes  but when it comes down to it you kind of do want encryption and decryption to be tough to figure out otherwise it will be easy to hack

User · Answer

You may be looking for the ProtectedData class  which encrypts data using the user s logon credentials

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If you need to store a password in memory and would like to have it encrypted you should use SecureString   http   msdn microsoft com en-us library system security securestring aspx  For more general uses I would use a FIPS approved algorithm such as Advanced Encryption Standard  formerly known as Rijndael  See this page for an implementation example   http   msdn microsoft com en-us library system security cryptography rijndael aspx

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Try this class   public class DataEncryptor       TripleDESCryptoServiceProvider symm        region Factory     public DataEncryptor                 this symm   new TripleDESCryptoServiceProvider            this symm Padding   PaddingMode PKCS7            public DataEncryptor TripleDESCryptoServiceProvider keys                this symm   keys             public DataEncryptor byte   key  byte   iv                this symm   new TripleDESCryptoServiceProvider            this symm Padding   PaddingMode PKCS7          this symm Key   key          this symm IV   iv              endregion       region Properties     public TripleDESCryptoServiceProvider Algorithm               get   return symm            set   symm   value              public byte   Key               get   return symm Key            set   symm Key   value              public byte   IV               get   return symm IV            set   symm IV   value                endregion       region Crypto      public byte   Encrypt byte   data    return Encrypt data  data Length         public byte   Encrypt byte   data  int length                try                          Create a MemoryStream              var ms   new MemoryStream                    Create a CryptoStream using the MemoryStream                 and the passed key and initialization vector  IV               var cs   new CryptoStream ms                  symm CreateEncryptor symm Key  symm IV                   CryptoStreamMode Write                   Write the byte array to the crypto stream and flush it              cs Write data  0  length               cs FlushFinalBlock                    Get an array of bytes from the                 MemoryStream that holds the                 encrypted data              byte   ret   ms ToArray                    Close the streams              cs Close                ms Close                    Return the encrypted buffer              return ret                    catch  CryptographicException ex                        Console WriteLine  A cryptographic error occured   0    ex Message                     return null             public string EncryptString string text                return Convert ToBase64String Encrypt Encoding UTF8 GetBytes text                public byte   Decrypt byte   data    return Decrypt data  data Length         public byte   Decrypt byte   data  int length                try                          Create a new MemoryStream using the passed                 array of encrypted data              MemoryStream ms   new MemoryStream data                   Create a CryptoStream using the MemoryStream                 and the passed key and initialization vector  IV               CryptoStream cs   new CryptoStream ms                  symm CreateDecryptor symm Key  symm IV                   CryptoStreamMode Read                   Create buffer to hold the decrypted data              byte   result   new byte length                   Read the decrypted data out of the crypto stream                and place it into the temporary buffer              cs Read result  0  result Length               return result                    catch  CryptographicException ex                        Console WriteLine  A cryptographic error occured   0    ex Message                     return null             public string DecryptString string data                return Encoding UTF8 GetString Decrypt Convert FromBase64String data    TrimEnd   0                endregion      and use it like this   string message  A very secret message here    DataEncryptor keys new DataEncryptor    string encr keys EncryptString message       later string actual keys DecryptString encr

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UPDATE 23 Dec 2015  Since this answer seems to be getting a lot of upvotes  I ve updated it to fix silly bugs and to generally improve the code based upon comments and feedback   See the end of the post for a list of specific improvements   As other people have said  Cryptography is not simple so it s best to avoid  rolling your own  encryption algorithm   You can  however   roll your own  wrapper class around something like the built-in RijndaelManaged cryptography class   Rijndael is the algorithmic name of the current Advanced Encryption Standard  so you re certainly using an algorithm that could be considered  best practice    The RijndaelManaged class does indeed normally require you to  muck about  with byte arrays  salts  keys  initialization vectors etc  but this is precisely the kind of detail that can be somewhat abstracted away within your  wrapper  class   The following class is one I wrote a while ago to perform exactly the kind of thing you re after  a simple single method call to allow some string-based plaintext to be encrypted with a string-based password  with the resulting encrypted string also being represented as a string   Of course  there s an equivalent method to decrypt the encrypted string with the same password   Unlike the first version of this code  which used the exact same salt and IV values every time  this newer version will generate random salt and IV values each time   Since salt and IV must be the same between the encryption and decryption of a given string  the salt and IV is prepended to the cipher text upon encryption and extracted from it again in order to perform the decryption   The result of this is that encrypting the exact same plaintext with the exact same password gives and entirely different ciphertext result each time   The  strength  of using this comes from using the RijndaelManaged class to perform the encryption for you  along with using the Rfc2898DeriveBytes function of the System Security Cryptography namespace which will generate your encryption key using a standard and secure algorithm  specifically  PBKDF2  based upon the string-based password you supply    Note this is an improvement of the first version s use of the older PBKDF1 algorithm    Finally  it s important to note that this is still unauthenticated encryption   Encryption alone provides only privacy  i e  message is unknown to 3rd parties   whilst authenticated encryption aims to provide both privacy and authenticity  i e  recipient knows message was sent by the sender      Without knowing your exact requirements  it s difficult to say whether the code here is sufficiently secure for your needs  however  it has been produced to deliver a good balance between relative simplicity of implementation vs  quality    For example  if your  receiver  of an encrypted string is receiving the string directly from a trusted  sender   then authentication may not even be necessary   If you require something more complex  and which offers authenticated encryption  check out this post for an implementation   Here s the code   using System  using System Text  using System Security Cryptography  using System IO  using System Linq   namespace EncryptStringSample       public static class StringCipher                  This constant is used to determine the keysize of the encryption algorithm in bits             We divide this by 8 within the code below to get the equivalent number of bytes          private const int Keysize   256              This constant determines the number of iterations for the password bytes generation function          private const int DerivationIterations   1000           public static string Encrypt string plainText  string passPhrase                           Salt and IV is randomly generated each time  but is preprended to encrypted cipher text                so that the same Salt and IV values can be used when decrypting                var saltStringBytes   Generate256BitsOfRandomEntropy                var ivStringBytes   Generate256BitsOfRandomEntropy                var plainTextBytes   Encoding UTF8 GetBytes plainText               using  var password   new Rfc2898DeriveBytes passPhrase  saltStringBytes  DerivationIterations                                 var keyBytes   password GetBytes Keysize   8                   using  var symmetricKey   new RijndaelManaged                                          symmetricKey BlockSize   256                      symmetricKey Mode   CipherMode CBC                      symmetricKey Padding   PaddingMode PKCS7                      using  var encryptor   symmetricKey CreateEncryptor keyBytes  ivStringBytes                                                 using  var memoryStream   new MemoryStream                                                          using  var cryptoStream   new CryptoStream memoryStream  encryptor  CryptoStreamMode Write                                                                 cryptoStream Write plainTextBytes  0  plainTextBytes Length                                   cryptoStream FlushFinalBlock                                       Create the final bytes as a concatenation of the random salt bytes  the random iv bytes and the cipher bytes                                  var cipherTextBytes   saltStringBytes                                  cipherTextBytes   cipherTextBytes Concat ivStringBytes  ToArray                                    cipherTextBytes   cipherTextBytes Concat memoryStream ToArray    ToArray                                    memoryStream Close                                    cryptoStream Close                                    return Convert ToBase64String cipherTextBytes                                                                                                                                    public static string Decrypt string cipherText  string passPhrase                           Get the complete stream of bytes that represent                  32 bytes of Salt     32 bytes of IV     n bytes of CipherText              var cipherTextBytesWithSaltAndIv   Convert FromBase64String cipherText                  Get the saltbytes by extracting the first 32 bytes from the supplied cipherText bytes              var saltStringBytes   cipherTextBytesWithSaltAndIv Take Keysize   8  ToArray                   Get the IV bytes by extracting the next 32 bytes from the supplied cipherText bytes              var ivStringBytes   cipherTextBytesWithSaltAndIv Skip Keysize   8  Take Keysize   8  ToArray                   Get the actual cipher text bytes by removing the first 64 bytes from the cipherText string              var cipherTextBytes   cipherTextBytesWithSaltAndIv Skip  Keysize   8    2  Take cipherTextBytesWithSaltAndIv Length -   Keysize   8    2   ToArray                 using  var password   new Rfc2898DeriveBytes passPhrase  saltStringBytes  DerivationIterations                                 var keyBytes   password GetBytes Keysize   8                   using  var symmetricKey   new RijndaelManaged                                          symmetricKey BlockSize   256                      symmetricKey Mode   CipherMode CBC                      symmetricKey Padding   PaddingMode PKCS7                      using  var decryptor   symmetricKey CreateDecryptor keyBytes  ivStringBytes                                                 using  var memoryStream   new MemoryStream cipherTextBytes                                                         using  var cryptoStream   new CryptoStream memoryStream  decryptor  CryptoStreamMode Read                                                                 var plainTextBytes   new byte cipherTextBytes Length                                   var decryptedByteCount   cryptoStream Read plainTextBytes  0  plainTextBytes Length                                   memoryStream Close                                    cryptoStream Close                                    return Encoding UTF8 GetString plainTextBytes  0  decryptedByteCount                                                                                                                                    private static byte   Generate256BitsOfRandomEntropy                         var randomBytes   new byte 32      32 Bytes will give us 256 bits              using  var rngCsp   new RNGCryptoServiceProvider                                     Fill the array with cryptographically secure random bytes                  rngCsp GetBytes randomBytes                             return randomBytes                      The above class can be used quite simply with code similar to the following   using System   namespace EncryptStringSample       class Program               static void Main string   args                        Console WriteLine  Please enter a password to use                 string password   Console ReadLine                Console WriteLine  Please enter a string to encrypt                 string plaintext   Console ReadLine                Console WriteLine                   Console WriteLine  Your encrypted string is                 string encryptedstring   StringCipher Encrypt plaintext  password               Console WriteLine encryptedstring               Console WriteLine                   Console WriteLine  Your decrypted string is                 string decryptedstring   StringCipher Decrypt encryptedstring  password               Console WriteLine decryptedstring               Console WriteLine                   Console WriteLine  Press any key to exit                   Console ReadLine                         You can download a simple VS2013 sample solution  which includes a few unit tests  here    UPDATE 23 Dec 2015  The list of specific improvements to the code are      Fixed a silly bug where encoding was different between encrypting and decrypting   As the mechanism by which salt  amp  IV values are generated has changed  encoding is no longer necessary  Due to the salt IV change  the previous code comment that incorrectly indicated that UTF8 encoding a 16 character string produces 32 bytes is no longer applicable  as encoding is no longer necessary   Usage of the superseded PBKDF1 algorithm has been replaced with usage of the more modern PBKDF2 algorithm  The password derivation is now properly salted whereas previously it wasn t salted at all  another silly bug squished

User · Answer

If you are targeting ASP NET Core that does not support RijndaelManaged yet  you can use IDataProtectionProvider   First  configure your application to use data protection   public class Startup       public void ConfigureServices IServiceCollection services                services AddDataProtection                         Then you ll be able to inject IDataProtectionProvider instance and use it to encrypt decrypt data   public class MyService   IService       private const string Purpose    my protection purpose       private readonly IDataProtectionProvider  provider       public MyService IDataProtectionProvider provider                 provider   provider             public string Encrypt string plainText                var protector    provider CreateProtector Purpose           return protector Protect plainText              public string Decrypt string cipherText                var protector    provider CreateProtector Purpose           return protector Unprotect cipherText             See this article for more details

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using System IO  using System Text  using System Security Cryptography   public static class EncryptionHelper       public static string Encrypt string clearText                string EncryptionKey    abc123           byte   clearBytes   Encoding Unicode GetBytes clearText           using  Aes encryptor   Aes Create                          Rfc2898DeriveBytes pdb   new Rfc2898DeriveBytes EncryptionKey  new byte     0x49  0x76  0x61  0x6e  0x20  0x4d  0x65  0x64  0x76  0x65  0x64  0x65  0x76                 encryptor Key   pdb GetBytes 32               encryptor IV   pdb GetBytes 16               using  MemoryStream ms   new MemoryStream                                  using  CryptoStream cs   new CryptoStream ms  encryptor CreateEncryptor    CryptoStreamMode Write                                         cs Write clearBytes  0  clearBytes Length                       cs Close                                      clearText   Convert ToBase64String ms ToArray                                     return clearText            public static string Decrypt string cipherText                string EncryptionKey    abc123           cipherText   cipherText Replace                    byte   cipherBytes   Convert FromBase64String cipherText           using  Aes encryptor   Aes Create                          Rfc2898DeriveBytes pdb   new Rfc2898DeriveBytes EncryptionKey  new byte     0x49  0x76  0x61  0x6e  0x20  0x4d  0x65  0x64  0x76  0x65  0x64  0x65  0x76                 encryptor Key   pdb GetBytes 32               encryptor IV   pdb GetBytes 16               using  MemoryStream ms   new MemoryStream                                  using  CryptoStream cs   new CryptoStream ms  encryptor CreateDecryptor    CryptoStreamMode Write                                         cs Write cipherBytes  0  cipherBytes Length                       cs Close                                      cipherText   Encoding Unicode GetString ms ToArray                                     return cipherText

[c#] Encrypting & Decrypting a String in C#

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