121 reputation
2
bio website
location United Kingdom
age
visits member for 3 years, 3 months
seen Sep 17 at 14:48

Sep
26
comment Is the last step of an iterated cryptographic hash still as resistant to preimage attacks as the original hash?
let us continue this discussion in chat
Sep
26
comment Is the last step of an iterated cryptographic hash still as resistant to preimage attacks as the original hash?
That proving cycle lengths is genuinely "hard" for real hash functions is no surprise. For practical purposes, I guess extensive simulation would provide me with adequate confidence... for example, if several million randomly chosen messages create a million non-repeating values each - then I'd feel less anxious. Do such studies exist, or would I need to do them myself?
Sep
26
comment Is the last step of an iterated cryptographic hash still as resistant to preimage attacks as the original hash?
Many thanks for the ref. I think I grasp what you meant by 'rho patterns' now. I still find your answer counter-intuitive... but guess that, if I could prove that repeated application always results in the large cycle, I'd be fully convinced. With my practical hat on, I wonder if some hashes can be shown to reliably have larger cycles than others? Must I accept these large cycles on faith, or are they proven? Is the answer the same if I use H(some-published-constant,m) in place of H(m)?
Sep
25
comment Is the last step of an iterated cryptographic hash still as resistant to preimage attacks as the original hash?
The other issue is whether or not the real hash function "is good"... If there is any narrowing of the state space, it strikes me that there must be a finite limit to the number of times the hash function can be recursively applied before there's insufficient entropy to assure security. It also strikes me as unlikely that all (any?) hash functions are entropy preserving when applied to values of the same length as the hash. In order to establish the limit, I'd need to estimate information loss on each application... but I don't know how to go about that.
Sep
25
comment Is the last step of an iterated cryptographic hash still as resistant to preimage attacks as the original hash?
Thanks for the answer... though there are a couple of things I'd like clarified. Do you have a reference regarding the "rho pattern"?
Sep
25
awarded  Student
Sep
25
awarded  Editor
Sep
25
revised Is the last step of an iterated cryptographic hash still as resistant to preimage attacks as the original hash?
added 14 characters in body
Sep
25
asked Is the last step of an iterated cryptographic hash still as resistant to preimage attacks as the original hash?