In this exercise you will implement the Birthday attack on SHA-1 from the previous lab using OpenSSL. The goal is to obtain a collision in the first four bytes of the hash.

You can implement the attack from scratch, or start from our archive here.

To compute a digest, you might find the code below useful:

    SHA_CTX context;
    SHA1_Init(&context);
    SHA1_Update(&context, buffer, length);
    SHA1_Final(md, &context); /* md must point to at least 20 bytes of valid memory */