What is a public key token and how is it calculated in assembly strong names?

Question

What is a 'public key token' and how is it calculated in assembly strong names?

Answer 1

Regarding your question, "How is it calculated", it's an SHA1 hash.

From dot net blog:

Microsoft solves the "public key bloat" problem by using a hash of the strongly-named assembly's public key. These hashes are referred to as public key tokens, and are the low 8 bytes of the SHA1 hash of the strongly-named assembly's public key. SHA1 hashes are 160 bit (20 byte) hashes, and the top 12 bytes of the hash are simply discarded in this algorithm.

Answer 2

You can get the PublicKeyToken from the VS Command Line by typing:

sn –T DLLName.dll

Answer 3

If you need to generate a public key token based on a full public key, this little static method works:

   private static byte[] GetKeyTokenFromFullKey(byte[] fullKey)
    {
        SHA1CryptoServiceProvider csp = new SHA1CryptoServiceProvider();
        byte[] hash = csp.ComputeHash(fullKey);
        byte[] token = new byte[8];
        for (int i = 0; i < 8; i++ )
            token[i] = hash[hash.Length - (i+1)];

        return token;
    }