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Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
1–10 of 17 posts
Re: Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
#2Sounds like a NP problem.
Re: Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
#3There's an infinite number of those strings, but barring an edge case in the md5 algorithm, none are known.
Re: Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
#4Simple answer: of course there is. The real challenge is finding such strings.
If I wanted to know the answer to that question, I'd first search some precomputed rainbow tables to see if anybody's gotten lucky:
Re: Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
#5Simple answer: of course there is. The real challenge is finding such strings. If I wanted to know the answer to that question, I'd first search some precomputed rainbow tables to see if anybody's gotten lucky: http://project-rainbowcrack.com/table.htm
Do you mean just that it is very very likely that there is, or is there some argument that the MD5 function must be surjective?
Re: Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
#6Simple answer: of course there is. The real challenge is finding such strings. If I wanted to know the answer to that question, I'd first search some precomputed rainbow tables to see if anybody's gotten lucky: http://project-rainbowcrack.com/table.htm
The discussion on security.SE seems to imply it's unknown: https://security.stackexchange.com/questions/107081/does-eve... so if you have a proof of your simple answer, I'm sure they'd welcome it
Re: Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
#7I tried seeing if there were any references in log files or forum questions to that, but the bad news is that your specific hash is also what one would get from an "invalid" hash, same as asking about the magic string "00000000000000000000000000000000"
Re: Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
#8Simple answer: of course there is. The real challenge is finding such strings. If I wanted to know the answer to that question, I'd first search some precomputed rainbow tables to see if anybody's gotten lucky: http://project-rainbowcrack.com/table.htm
The discussion on security.SE seems to imply it's unknown: https://security.stackexchange.com/questions/107081/does-eve... so if you have a proof of your simple answer, I'm sure they'd welcome it
The linked answer on SE basically says statistically there's a near-100% chance that there's a string where md5(string) is 0xfffffff... but there's no concrete proof.
Which is basically the same thing the GP says.
Re: Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
#9Simple answer: of course there is. The real challenge is finding such strings. If I wanted to know the answer to that question, I'd first search some precomputed rainbow tables to see if anybody's gotten lucky: http://project-rainbowcrack.com/table.htm
The discussion on security.SE seems to imply it's unknown: https://security.stackexchange.com/questions/107081/does-eve... so if you have a proof of your simple answer, I'm sure they'd welcome it
My statement is one of statistically-informed confidence. A physicist's proof, not a mathematician's. As I said, proving it is where the challenge lies.
Re: Ask HN: Is there a string which MD5 Sum is all 0xffffffffffff?
#10Assuming you meant a 128-bit hash with all bits set to '1' (i.e., '0xffffffffffffffffffffffffffffffff'), it would still be extremely difficult, if not practically impossible, to find a string that hashes to this specific value. The MD5 algorithm is designed to produce seemingly random output for small changes in input, and there are no known methods to easily reverse-engineer an MD5 hash.
That being said, MD5 is no longer considered cryptographically secure due to vulnerabilities discovered over the years, such as hash collisions. But finding a specific hash, like the one you mentioned, would still require a brute-force attack or an advanced cryptanalytic method, neither of which is guaranteed to succeed.