3 ms·
The "second" in "second preimage" doesn't refer to hashing something twice. It means that you already have one preimage for a hash (presumably because you star
by comex 9y ago
The "second" in "second preimage" doesn't refer to hashing something twice. It means that you already have one preimage for a hash (presumably because you started with the "preimage" and calculated the hash from that), and you want to find a second, different one.
- QML 9y agoIn simpler terms, given H(x), it is impossible to find x’ such that H(x’) == H(x) in polynomial time.
- comex 9y agoTo be pedantic: given x and H(x), it is impossible to find x’ such that H(x’) == H(x) in a practical amount of time. (You need x, and an attack doesn't need to be polynomial to break the hash function; it just needs to be fast enough, considering constant factors, to fit within some plausible attacker's computational resources.)