MD5 (message digest algorithm) or other hashes are one way functions that produce a "fingerprint". essentially, they map something with a lot of bits down to just a few bits (128 in the case of MD5) in such a way that collisions are as rare as possible.

this is useful because you can compare and store these small hashes much more easily than the entire original sequences. in cryptography, one-way hashes are used to verify something without necessarily giving away the original information. eg, unix stores hashes of passwords instead of the passwords themselves. when a user enters their password, the system computes the hash of it and compares it to the hashes listed in /etc/passwd. since you can't run the hash function in reverse, the system knows that the password you entered is the right one. the crypt that unix uses doesn't really reduce the size but is a similar idea. hashes and digests like MD5 are an integral part of digital signatures.

MD5 is just one of many hashing algorithms. it was developed by Ronald Rivest (the R in RSA) in 1991. it's an updated version of MD4. there's also SHA-1 (Secure Hash Algorithm), developed by NIST in conjunction with the NSA and produces 160 bit digest. it's more collision resistant than MD5 and is the most commonly used hash for cryptographic purposes these days. there are others, but these are the important ones.

anders pearson

In reply to Re: What is MD5 Hashing and Why is it Important? by thraxil
in thread What is MD5 Hashing and Why is it Important? by princepawn

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