Encrypt, decrypt and generate a key in C# using AES256.

encryption.cs

#region Encryption
/// <summary>
/// Generate a private key
/// From : www.chapleau.info/blog/2011/01/06/usingsimplestringkeywithaes256encryptioninc.html
/// </summary>
private static string GenerateKey(int iKeySize)
{
    RijndaelManaged aesEncryption = new RijndaelManaged();
    aesEncryption.KeySize = iKeySize;
    aesEncryption.BlockSize = 128;
    aesEncryption.Mode = CipherMode.CBC;
    aesEncryption.Padding = PaddingMode.PKCS7;
    aesEncryption.GenerateIV();
    string ivStr = Convert.ToBase64String(aesEncryption.IV);
    aesEncryption.GenerateKey();
    string keyStr = Convert.ToBase64String(aesEncryption.Key);
    string completeKey = ivStr + "," + keyStr;

    return Convert.ToBase64String(ASCIIEncoding.UTF8.GetBytes(completeKey));
}  

/// <summary>
/// Encrypt
/// From : www.chapleau.info/blog/2011/01/06/usingsimplestringkeywithaes256encryptioninc.html
/// </summary>
private static string Encrypt(string iPlainStr, string iCompleteEncodedKey, int iKeySize)
{
    RijndaelManaged aesEncryption = new RijndaelManaged();
    aesEncryption.KeySize = iKeySize;
    aesEncryption.BlockSize = 128;
    aesEncryption.Mode = CipherMode.CBC;
    aesEncryption.Padding = PaddingMode.PKCS7;
    aesEncryption.IV = Convert.FromBase64String(ASCIIEncoding.UTF8.GetString(Convert.FromBase64String(iCompleteEncodedKey)).Split(',')[0]);
    aesEncryption.Key = Convert.FromBase64String(ASCIIEncoding.UTF8.GetString(Convert.FromBase64String(iCompleteEncodedKey)).Split(',')[1]);
    byte[] plainText = ASCIIEncoding.UTF8.GetBytes(iPlainStr);
    ICryptoTransform crypto = aesEncryption.CreateEncryptor();         
    byte[] cipherText = crypto.TransformFinalBlock(plainText, 0, plainText.Length);
    return Convert.ToBase64String(cipherText);
}

/// <summary>
/// Decrypt
/// From : www.chapleau.info/blog/2011/01/06/usingsimplestringkeywithaes256encryptioninc.html
/// </summary>
private static string Decrypt(string iEncryptedText, string iCompleteEncodedKey, int iKeySize)
{
    RijndaelManaged aesEncryption = new RijndaelManaged();
    aesEncryption.KeySize = iKeySize;
    aesEncryption.BlockSize = 128;
    aesEncryption.Mode = CipherMode.CBC;
    aesEncryption.Padding = PaddingMode.PKCS7;
    aesEncryption.IV = Convert.FromBase64String(ASCIIEncoding.UTF8.GetString(Convert.FromBase64String(iCompleteEncodedKey)).Split(',')[0]);
    aesEncryption.Key = Convert.FromBase64String(ASCIIEncoding.UTF8.GetString(Convert.FromBase64String(iCompleteEncodedKey)).Split(',')[1]);
    ICryptoTransform decrypto = aesEncryption.CreateDecryptor();
    byte[] encryptedBytes = Convert.FromBase64CharArray(iEncryptedText.ToCharArray(), 0, iEncryptedText.Length);
    return ASCIIEncoding.UTF8.GetString(decrypto.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length));
}
#endregion