AES Encryption Error: Padding is invalid and cannot be removed

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; }