Got Error: “Specified block size is not valid for this algorithm” while initialize AesCryptoProvider

Question

I am trying to use larger block size for the AES Encryption:

private static void EncryptFile(string inFile, RSACryptoServiceProvider rsaPublicKey)
{
    using (AesCryptoServiceProvider aes = new AesCryptoServiceProvider())
    {
        // Create instance of AesManaged for
        // symetric encryption of the data.
        aes.KeySize = 256;

        // Allocating 64K
        aes.BlockSize = 8 * 1024 * 64; 
    }
}

and hitting the following exception:

System.Security.Cryptography.CryptographicException was unhandled
Message=Specified block size is not valid for this algorithm.
Source=mscorlib StackTrace: at System.Security.Cryptography.SymmetricAlgorithm.set_BlockSize(Int32 value) at ConsoleApplication4.Program.EncryptFile(String inFile, RSACryptoServiceProvider rsaPublicKey) in C:\\Projects\\ConsoleApplication4\\Program.cs:line 117

I sure am missing somehting ovbious, any clue?

Answer 1

It appears that AES only supports block size equal to 128. It appears that you can get around this by processing your data as multiple blocks.

source

Answer 2

Only certain block sizes are supported by each algorithm.

See SymmetricAlgorithm.LegalBlockSizes .