Hashing Algorithms

MD5

I often see the MD5 hashing algorithm used incorrectly. And while most databases support it by default, MD5 has been mathematically proven to be insecure. Given MD5, it is trivially easy to produce collisions on modern hardware. We’ve already seen it produce collisions earlier.

One of the most notable examples occurred in 2005. Researchers were able to generate collisions in MD5 checksums using a laptop. The significance of this is that it doesn’t take a $200k beast of a server to break MD5, just any old laptop, and that was in 2005. In 2005 people, that was like 100 internet years ago. No more MD5 for password hashing, please. Non-secure hashes to verify data contents, sure. Just not for secure hashes that an attacker would be interested in breaking.

MD5 is not entirely broken since it is still mostly secure when used with a suitable salt. But I still recommend that you should move on to a more future proof solution.

SHA-1

Ah, good old SHA-1, trusty and secure for years. Those are IRLIn Real Life years too; in internet years, that’s decades. In 2005 (a bad year for security apparently), researchers from Shandong University released a paper proving that SHA-1 collisions could be reliably generated with less than $2^{69}$ hash operations. Collisions at around $2^{80}$ hashing operations are considered safe cryptographically. $2^{80}$ is about $1.20892\times 10^{24}$, so “cryptographically secure” is very secure. Since then, Moore’s law has ensured that SHA-1 is even less secure and should be avoided in any application that needs true security.

As with MD5, SHA1 is still algorithmically secure when used with a random salt.

SHA-256 / SHA-512

In 2001, the SHA-2 standard was introduced as a successor for SHA-1. When SHA-1 was proven to be insecure in 2005, SHA-2 became very popular. SHA-256 and SHA-512 are essentially the same. SHA-256 uses 32-bit words and SHA-512 uses 64-bit words. They also have a different number of rounds. But the core algorithm is practically identical.

SHA-2 is currently considered cryptographically secure with no known vulnerabilities when used with a sufficient number of rounds (>64).