AES Encryption Error: Padding is invalid and cannot be removed

Question

Can anyone help me on the below code, error is padding is invalid and cannot be removed. I am searching all over SO and applied all their suggestions, but still padding is invalid. I am using NET-2.0

Below is my code

static public String AES_encrypt(String Input)
    {
        string AES_Key = "PSVJQRk9QTEpNVU1DWUZCRVFGV1VVT0ZOV1RRU1NaWQ=";
        string AES_IV = "YWlFLVEZZUFNaWlhPQ01ZT02qWU5HTFJQVFNCRUJZVA=";
        var aes = new RijndaelManaged();
        aes.KeySize = 256;
        aes.BlockSize = 256;
        aes.Padding = PaddingMode.PKCS7;
        aes.Key = Convert.FromBase64String(AES_Key);
        aes.IV = Convert.FromBase64String(AES_IV);

        var encrypt = aes.CreateEncryptor(aes.Key, aes.IV);
        byte[] xBuff = null;
        using (var ms = new MemoryStream())
        {
            using (var cs = new CryptoStream(ms, encrypt, CryptoStreamMode.Write))
            {
                byte[] xXml = Encoding.UTF8.GetBytes(Input);
                cs.Write(xXml, 0, xXml.Length);
            }

            xBuff = ms.ToArray();
        }

        String Output = Convert.ToBase64String(xBuff);
        return Output;
    }

    static public String AES_decrypt(String Input)
    {
        string AES_Key = "PSVJQRk9QTEpNVU1DWUZCrOFGV1VVT0ZOV1RRU1NaWQ=";
        string AES_IV = "YWlFLVEZZUFNaWlhPQ01ZT02qWU5HTFJQVFNCRUJZVA=";
        RijndaelManaged aes = new RijndaelManaged();
        aes.KeySize = 256;
        aes.BlockSize = 256;
        aes.Mode = CipherMode.CBC;
        aes.Padding = PaddingMode.PKCS7;
        aes.Key = Convert.FromBase64String(AES_Key);
        aes.IV = Convert.FromBase64String(AES_IV);

        var decrypt = aes.CreateDecryptor();
        byte[] xBuff = null;
        using (var ms = new MemoryStream())
        {
            using (var cs = new CryptoStream(ms, decrypt, CryptoStreamMode.Write))
            {
                byte[] xXml = Convert.FromBase64String(Input);
                cs.Write(xXml, 0, xXml.Length);
            }

            xBuff = ms.ToArray();
        }

        String Output = Encoding.UTF8.GetString(xBuff);
        return Output;
    }

I am thinking the issues here is the AES_encrypt, because if I passed an encrypted string from PHP to my project, AES_decrypt will successfully decrypt it. However, whenever I use AES_encrypt, AES_decrypt is throwing error.

Any help would be greatly appreciated.

Answer 1

Mahr - as Patrick has pointed out I should have taken the time to explain the changes I have made from your original..

Firstly your decryptor is created without any parameters & as such it doesn't understand the ciperkey to use Secondly the key & IV are in Bytes so you must divide by 8 before passing in the key sizes

I've also added a few extras to prevent further issues 1: You must clear the RijndaelManaged object when your're done with it 2: I've simplified the string conversion to make it a little clearer 3: And this is only because I like them I've created the methods as extension methods for easier use.

This should work..

private static byte[] _salt = Encoding.ASCII.GetBytes("o6806642kbM7c5");

    /// <summary>
    /// Encrypt the given string using AES.  The string can be decrypted using 
    /// DecryptStringAES().  The sharedSecret parameters must match.
    /// </summary>
    /// <param name="plainText">The text to encrypt.</param>
    /// <param name="sharedSecret">A password used to generate a key for encryption.</param>
    public static string EncryptStringAES(this string plainText)
    {
        string sharedSecret = "abcd";
        if (string.IsNullOrEmpty(plainText))
            throw new ArgumentNullException("plainText");
        if (string.IsNullOrEmpty(sharedSecret))
            throw new ArgumentNullException("sharedSecret");

        string outStr = null;                       // Encrypted string to return
        RijndaelManaged aesAlg = null;              // RijndaelManaged object used to encrypt the data.

        try
        {
            // generate the key from the shared secret and the salt
            Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, _salt);

            // Create a RijndaelManaged object
            // with the specified key and IV.
            aesAlg = new RijndaelManaged();
            aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);
            aesAlg.IV = key.GetBytes(aesAlg.BlockSize / 8);

            // Create a decrytor to perform the stream transform.
            ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.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);
                    }
                }
                outStr = Convert.ToBase64String(msEncrypt.ToArray());
            }
        }
        finally
        {
            // Clear the RijndaelManaged object.
            if (aesAlg != null)
                aesAlg.Clear();
        }

        // Return the encrypted bytes from the memory stream.
        return outStr;
    }

    /// <summary>
    /// Decrypt the given string.  Assumes the string was encrypted using 
    /// EncryptStringAES(), using an identical sharedSecret.
    /// </summary>
    /// <param name="cipherText">The text to decrypt.</param>
    /// <param name="sharedSecret">A password used to generate a key for decryption.</param>
    public static string DecryptStringAES(this string cipherText)
    {
        string sharedSecret = "abcd";
        if (string.IsNullOrEmpty(cipherText))
            throw new ArgumentNullException("cipherText");
        if (string.IsNullOrEmpty(sharedSecret))
            throw new ArgumentNullException("sharedSecret");

        // Declare the RijndaelManaged object
        // used to decrypt the data.
        RijndaelManaged aesAlg = null;

        // Declare the string used to hold
        // the decrypted text.
        string plaintext = null;

        try
        {
            // generate the key from the shared secret and the salt
            Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, _salt);

            // Create a RijndaelManaged object
            // with the specified key and IV.
            aesAlg = new RijndaelManaged();
            aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);
            aesAlg.IV = key.GetBytes(aesAlg.BlockSize / 8);

            // Create a decrytor to perform the stream transform.
            ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
            // Create the streams used for decryption.                
            byte[] bytes = Convert.FromBase64String(cipherText);
            using (MemoryStream msDecrypt = new MemoryStream(bytes))
            {
                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();
                }
            }
        }
        finally
        {
            // Clear the RijndaelManaged object.
            if (aesAlg != null)
                aesAlg.Clear();
        }

        return plaintext;
    }