Today I’m going to discuss about MD5 Collision Attack. But before proceeding, I’ll just give a brief on the HAsh function. A “hash” (also called a “digest”, and informally a “checksum”) is a kind of “signature” for a stream of data that represents the contents. The closest real-life analog we can think is “a tamper-evident seal on a software package”: if you open the box (change the file), it’s detected.
So what is an MD5 Collision Attack and how is it constructed ?? Before going at this stage, let me first explain what hashing really means ! The very first point here is, to understand that hashing is NOT encryption. This is a common confusion, especially because all these words are in the category of “cryptography”, but it’s important to understand the difference. “Encryption” transforms data from a cleartext to ciphertext and back (given the right keys). Thus we see that “Encryption” is a two-way operation. Hashes, on the other hand, are stream of data into small digest, and it’s strictly a one way operation. All hashes of the same type – (this example shows the “MD5″ variety) – have the same size no matter how big the inputs are.