Re:Illegal Hashes
by saghm on Monday November 28, 2022 @07:06PM
(#33781755)
>> Because MD5 is a relatively weak algorithm, it is possible to create deliberate hash "collisions". That is, take some data and manipulate it until it has the same MD5 as a different piece of data.
> First sentence is true. Second sentence is false - that's called a preimage attack. MD5 is broken for collisions, not preimage or second preimage.
>> It is somewhat cheap and easy to produce a file with a specific SHA-1 hash.
> No, that's called a second preimage attack. SHA-1 is broken for collision, not preimage or second preimage
To use an analogy people might be familiar with, it's like the birthday paradox; you can find two people with the same birthday without looking too hard, but it's a lot more work to start with one person's birthday and then try to find someone else with that exact birthday. Right now, we can fairly easily find pairs of MD5/SHA1 hashes that are the same, but it's not currently feasible to start with one input to the hash function and then find some different input that produces the exact same hash.
> First sentence is true. Second sentence is false - that's called a preimage attack. MD5 is broken for collisions, not preimage or second preimage.
>> It is somewhat cheap and easy to produce a file with a specific SHA-1 hash.
> No, that's called a second preimage attack. SHA-1 is broken for collision, not preimage or second preimage
To use an analogy people might be familiar with, it's like the birthday paradox; you can find two people with the same birthday without looking too hard, but it's a lot more work to start with one person's birthday and then try to find someone else with that exact birthday. Right now, we can fairly easily find pairs of MD5/SHA1 hashes that are the same, but it's not currently feasible to start with one input to the hash function and then find some different input that produces the exact same hash.