如何为现有哈希添加值？

Question

For instance, I do an MD5 of "hashable" using:

        protected string hexHashMD5(byte[] filePart) {
        // Now that we have a byte array we can ask the CSP to hash it
        MD5 md5 = new MD5CryptoServiceProvider();
        byte[] result = md5.ComputeHash(filePart);

        // Build the final string by converting each byte
        // into hex and appending it to a StringBuilder
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < result.Length; i++) {
            sb.Append(result[i].ToString("X2"));
        }

        // And return it
        return sb.ToString();
    }

and store it's output into a string variable in my program. How can I take that Hash and add another byte[] to create a new hash?

I've been told that you can use file stream, to automatically stream in a bit at a time, and make the full hash, but what happens when I need to hash two separate files together?

Answer 1

You can make a custom Stream class that reads the two streams in order, then pass that to ComputeHash .

Alternatively, you can read both streams one block at a time and pass each block to TransformBlock :

byte[] buffer = new byte[4096];
while (true) {
    int read = stream1.Read(buffer, 0, buffer.Length);
    if (read == 0) break;
    hash.TransformBlock(buffer, 0, read, null, 0);
}

while (true) {
    int read = stream2.Read(buffer, 0, buffer.Length);
    if (read == 0) break;
    hash.TransformBlock(buffer, 0, read, null, 0);
}

hash.TransformFinalBlock(new byte[0], 0, 0);
var hashCode = hash.Hash;