4 ms·
"SHA1 and other hash algorithms generate a digital fingerprint that in theory is unique for each different file or text input they sign." ... and there it goes
by brongondwana 12y ago
"SHA1 and other hash algorithms generate a digital fingerprint that in theory is unique for each different file or text input they sign."
... and there it goes, any credibility I would give the author. There's dumbing down the content for a non-technical audience, and there's not understanding.
- blibble 12y agowhat's wrong with that statement exactly?
- waitwhat 12y agomaybe the use of "sign"?
- silentOpen 12y agoTwo things: 1. Hashes don't "sign" things (not directly anyway) 2. Hashes aren't unique in theory or practice (using a 256-bit hash on every 257-bit number will generate 2^256 collisions by the pigeonhole principle).
- Retric 12y agoHigh quality hashes are unique in practice. Suppose every person generates 1 billion files a second * 7 billion people * 1,000 years = ~3x10 ^ 28 call it 10^29. For a collusion among non identical files using a good 256 bit hash you get ~1/(2^256) * (10^29) * (10^29) = ~1/(2^198). Or 1 chance in ~4 * 10 ^ 59 of finding even one collision.
- nly 12y agoYour math is off a bit[0][1] but you're right, it's a vanishingly small probability of a single collision. This is fairly academic though, when you're talking about an adversary exploiting weaknesses in the algorithm itself, and not a perfect PRF. [0] http://preshing.com/20110504/hash-collision-probabilities/ http://preshing.com/20110504/hash-collision-probabilities/ [1] http://www.wolframalpha.com/input/?i=%281+billion+*+7+billion+per+second+*+1000+years%29^2+%2F+%282+*+2^256%29 http://www.wolframalpha.com/input/?i=%281+billion+*+7+billio...
- Retric 12y agoOps, when counting exponents make sure there in the same base.
- konklone 12y agoI could have said "practically unique", instead of "in theory is unique" there, but I make the distinction more clear just below that and note that there are always collisions out there.