Is HashAlgorithm.ComputeHash() stateful?

Question

I need to compute hashes of multiple blocks of data independently. Something like this:

using( HashAlgorithm hasher = new ActualHashAlgorithm() ) {
    for( int i = 0; i = numberOfBlocks; i++ ) {
        byte[] block = getBlock( i );
        byte[] hash = hasher.ComputeHash( block );
        // use hash
    }
}

Can I reuse the same HashAlgorithm object between blocks? Will HashAlgorithm reset state between calls to ComputeHash() or do I need to dispose the HashAlgorithm object and create new one for each new block of data?

Answer 1

Actually, when you need hash under .NET framework, I strongly recommended coding this function manually but not to use .NET framework.

Some months age, I immigrated a 32bit .NET program into 64bit windows. The program is crashed. At least I found hash value is different under different 32/64bit system, although same .NET program. I used Djb algorithm instead of .NET hash algorithm, and the program run okay.

This document is about Djb hash algorithm, you can rewrite by C#. It is not a hard work.

• DJB Hash Function

Answer 2

Using ComputeHash is usually stateless although it depends on the actual implementation... you can check that at runtime by accessing State after the call to ComputeHash...

see

• http://msdn.microsoft.com/en-us/library/s02tk69a.aspx
• http://msdn.microsoft.com/en-us/library/system.security.cryptography.hashalgorithm.transformblock.aspx
• http://msdn.microsoft.com/en-us/library/system.security.cryptography.hashalgorithm.transformfinalblock.aspx
• http://msdn.microsoft.com/en-us/library/system.security.cryptography.hashalgorithm.state.aspx