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I am trying to perform AES 256-bit CBC encryption in C#. I am using the sample key/iv strings from this page: http://pic.dhe.ibm.com/infocenter/initiate/v9r5/topic/com.ibm.einstall.doc/topics/t_einstall_GenerateAESkey.html

However when I run the function below, I receive an error saying "Specified key is not a valid size for this algorithm." when attempting to set cipher.Key. I am able to use this key/iv combination in a node.js project, but I am attempting to port it to C# to no avail. What am I doing wrong below?

    static void Main(string[] args)
    {
        string keyString = "B374A26A71490437AA024E4FADD5B497FDFF1A8EA6FF12F6FB65AF2720B59CCF";
        string ivString = "7E892875A52C59A3B588306B13C31FBD";

        byte[] key = Encoding.UTF8.GetBytes(keyString);
        byte[] iv = Encoding.UTF8.GetBytes(ivString);

        Console.WriteLine("Key is " + key.Length + " bytes.");

        using (RijndaelManaged cipher = new RijndaelManaged())
        {
            cipher.Mode = CipherMode.CBC;
            cipher.KeySize = 256;
            cipher.BlockSize = 128;
            cipher.Key = key;
            cipher.IV = iv;

            // Create a decrytor to perform the stream transform.
            ICryptoTransform encryptor = cipher.CreateEncryptor(cipher.Key, cipher.IV);
        }

        Console.WriteLine("Success!");
        Console.ReadKey();
    }
jkriddle
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2 Answers2

10

That key string is 64 characters long which is 512 bits, not 256. It looks like the string contains 32 hexadecimal values but then you need to do this instead:

byte[] key = new byte[] { 0xB3, 0x74, 0xA2, 0x6A, 0x71, 0x49, 0x04 etc. };
user469104
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  • Ah, thank you very much! It did indeed contain 32 hex values, so I just had to convert the string to hex (using this solution http://stackoverflow.com/questions/321370/convert-hex-string-to-byte-array) and then retrieve the bytes. – jkriddle Oct 15 '14 at 18:53
2

AES provides below bits based on secret key size.

16 length key size then AES-128 bit will be applicable. 24 length key size then AES-192 bit will be applicable. 32 length key size then AES-256 will be applicable.

Key sizes: 128, 192 or 256 bits Rounds: 10, 12 or 14 (depending on key size)

Asif Syed
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