CODEWITHSUNDEEP
c#.netencryptioncryptographyaes
user1260967
user1260967

Reputation: 99

aes decryption not working properly sometime

I am using aes for encryption/decryption of the text but sometime its giving me exact value after decryption while some times i am getting error. I referred to different answers over but didn't get the root cause of my problem .

private static string DecryptStringFromBytes(byte[] cipherText, byte[] key, byte[] iv)
    {
        // Declare the string used to hold the decrypted text.  
        string plaintext = null;

        // Create an RijndaelManaged object  
        // with the specified key and IV.  
        using (var rijAlg = new System.Security.Cryptography.RijndaelManaged())
        {
            //Settings  
            rijAlg.Mode = System.Security.Cryptography.CipherMode.CBC;
            rijAlg.Padding = System.Security.Cryptography.PaddingMode.PKCS7;
            rijAlg.FeedbackSize = 128;

            rijAlg.Key = key;
            rijAlg.IV = iv;

            // Create a decrytor to perform the stream transform.  
            var decryptor = rijAlg.CreateDecryptor(rijAlg.Key, rijAlg.IV);

            try
            {
                // Create the streams used for decryption.  
                using (var msDecrypt = new System.IO.MemoryStream(cipherText))
                {
                    using (var csDecrypt = new System.Security.Cryptography.CryptoStream(msDecrypt, decryptor, System.Security.Cryptography.CryptoStreamMode.Read))
                    {

                        using (var srDecrypt = new System.IO.StreamReader(csDecrypt))
                        {
                            // Read the decrypted bytes from the decrypting stream  
                            // and place them in a string.  
                            plaintext = srDecrypt.ReadToEnd();
                        }
                    }
                }
            }
            catch
            {
                plaintext = "keyError";
            }
        }
        return plaintext;
    }

It throws error "Padding is invalid and cannot be removed" I seen some suggestion like to remove padding but it didn't seems proper solution. I am not able to find the cause behind this as sometimes it runs perfectly without throwing error .

Any help or suggestion is really appreciated.

For Encryption - The encryption is being done on to client side in js and passing encryped text to server.

var key = CryptoJS.enc.Utf8.parse("16 digit number here");
            var iv = CryptoJS.enc.Utf8.parse("16 digit number here");
            var EncryptedString = CryptoJS.AES.encrypt(CryptoJS.enc.Utf8.parse("entered string to encrypt"), key,
             { keySize: 128 / 8, iv: iv, mode: CryptoJS.mode.CBC, padding: CryptoJS.pad.Pkcs7 });

Upvotes: 0

Views: 1729

Answers (1)

Iridium
Iridium

Reputation: 23731

By using a similar encryption routine in .NET to the decryption function you give I was able to successfully round-trip plaintext to ciphertext and back to plaintext, so it seems that the decryption function itself is ok. It therefore seems very likely that the key and/or IV you're using to encrypt does not match byte-for-byte with the values you're using when decrypting.

Given that your encryption code is using the UTF-8 encoded version of string values to form the key and IV, it would be worth doing the same in your decryption code (using Encoding.UTF8.GetBytes()).

However, it would be worth noting that whilst this might resolve the immediate issue, it is in itself a bad practice to use string values directly for keys without some form of key-derivation process (e.g. Rfc2898DeriveBytes), and IVs should be generated randomly for every application of the encryption function. Those are just a few issues with your use of cryptography (and are independent of whether the code works or not).

Upvotes: 1

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