4 ms·
MD5 may not be collision resistant, but the logic in your conclusion is completely wrong. There is no feasible pre-image attack on MD5. The MD5 generated _was n
by pxx 4y ago
MD5 may not be collision resistant, but the logic in your conclusion is completely wrong. There is no feasible pre-image attack on MD5. The MD5 generated _was not arbitrary_; they seem to have just brute-forced a few of the leading bytes and then did a Nostradamus attack.
Again: finding something that hashes to an arbitrary MD5 sum is still not known to be feasible. This isn't a particularly good reason to use MD5, but this also means that MD5 is not broken in the way you think it is.
When somebody finds something that hashes to all zeroes you can finally say that MD5 is completely broken. It is not known to be at that point yet.
- TillE 4y agoRight. Nobody should use MD5 if at all possible, but it's important to understand how it is and isn't broken. Like, if I have the MD5 hash of a binary from a trusted source, I can basically rely on that, unless the attacker was involved in producing the trusted binary. In which case I'd usually have bigger concerns.
- dingosity 4y agoNo. MD5 is broken. You can find a pre-image faster than brute force. This is the definition of "broken" for a hash function. https://link.springer.com/chapter/10.1007/978-3-642-01001-9_8 https://link.springer.com/chapter/10.1007/978-3-642-01001-9_...
- charcircuit 4y agoThat is "a" definition and that definition doesn't apply to the way the other commenter used broken.
- dingosity 4y agoThat is the definition for hash functions. The other commenter was, not to put too fine a point on it, wrong. From Schneier's Self-Study Course in Block-Cipher Cryptanalysis: "Breaking a cipher simply means finding a weakness in the cipher that can be exploited with a complexity less than brute-force." But please go on about how you know more than Schneier.
- dingosity 4y agohttps://www.schneier.com/wp-content/uploads/2016/02/paper-self-study.pdf https://www.schneier.com/wp-content/uploads/2016/02/paper-se...
- prvit 4y agoYou're disregarding the context of those words. Schneier is illustrating the gap between the academic and practical meanings of "broken".
- dingosity 4y agoThe term you're looking for is "compromised."
- pxx 4y agoThis is not a feasible attack. There is a large difference between how academics use "broken" and what the practical consequences are. As Schneier writes as an introduction in the very paragraph you are trying to quote, "in academic cryptography, the rules are relaxed considerably." This is not a snub on academia; colloquial terms sometimes just mean something different than the academic definition.