/// <summary>
/// Decrypts the given encrypted text using the given key.
/// </summary>
/// <param name="cipherText">The encrypted text</param>
/// <param name="keyBytes">The key to use</param>
/// <returns>The decrypted text</returns>
public static string DecryptAES(string cipherText, byte[] keyBytes)
{
//DO NOT DECRYPT EMPTY STRING
if (string.IsNullOrEmpty(cipherText))
{
return(string.Empty);
}
//DO NOT DECRYPT IF THERE IS NO CRYPT KEY
if ((keyBytes == null) || (keyBytes.Length == 0))
{
return(cipherText);
}
// STORAGE FOR DATA DECODED FROM BASE64
byte[] ivPlusCipher;
try
{
// DECODE THE BASE64 DATA
ivPlusCipher = Convert.FromBase64String(cipherText);
}
catch (System.FormatException)
{
// DATA WAS NOT VALID BASE64, IT CANNOT BE DECRYPTED
return(cipherText);
}
// THE DECRYPTED DATA MUST BE AT LEAST 17 BYTES (AND PROBABLY LONGER)
if (ivPlusCipher.Length <= 16)
{
return(cipherText);
}
//CONVERT CIPHER TEXT TO BYTES
try
{
//SPLIT THE IV (FIRST 128 BITS) AND CIPHER TEXT
byte[] ivBytes = new byte[16];
byte[] cipherTextBytes = new byte[ivPlusCipher.Length - 16];
System.Buffer.BlockCopy(ivPlusCipher, 0, ivBytes, 0, 16);
System.Buffer.BlockCopy(ivPlusCipher, 16, cipherTextBytes, 0, cipherTextBytes.Length);
//CONFIGURE AES
RijndaelManaged symmetricKey = new RijndaelManaged();
symmetricKey.Mode = CipherMode.CBC;
symmetricKey.Key = keyBytes;
symmetricKey.IV = ivBytes;
//CREATE DECRYPTOR
ICryptoTransform decryptor = symmetricKey.CreateDecryptor();
//CREATE BUFFER TO HOLD DECRYPTED TEXT
byte[] plainTextBytes = new byte[cipherTextBytes.Length];
int decryptedByteCount;
//CREATE MEMORY STREAM OF DECRYPTED DATA
using (MemoryStream memoryStream = new MemoryStream(cipherTextBytes))
{
//CREATE THE CRYPTO STREAM
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
{
//DECRYPT THE CIPHER TEXT
decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
//CLOSE CRYPTO STREAM
cryptoStream.Close();
}
//CLOSE MEMORY STREAM
memoryStream.Close();
}
//CONVERT DECRYPTED BYTES TO STRING
string plainText = Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);
//RETURN DECRYPTED TEXT
return(plainText);
}
catch (Exception ex)
{
//SOMETHING WENT WRONG, RETURN ORIGINAL VALUE
string scriptName = HttpContextHelper.GetCurrentScriptName();
Logger.Debug("Error decrypting value " + cipherText + " in script " + scriptName, ex);
return(cipherText);
}
}
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