123 reputation
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bio website about.me/ClaudioFloreani
location
age 35
visits member for 1 year, 5 months
seen May 12 '13 at 11:05

Born in Milan the 4th of february 1979, I lived all the informatic revolution in Italy, subscribing to the first ISP (Agorà) even before the WWW, and working for first FTTH broadband access provider (Fastweb) and then for the first UMTS mobile broadband provider (H3G). I believe in the disruptive power of the bits, and realizing that there's still much to do in the Internet I decided to take my part, founding Crevel, a platform to gives back to the people the personal dimension of the travel.


Sep
24
awarded  Autobiographer
May
3
awarded  Scholar
May
3
accepted Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?
May
2
comment Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?
Can you prove that if H(s,r)=d returns a different digest d for each r and R(d)=r, so there are $d_1(r_1), d_2(r_2), d_3(r_3)$ possible valid hash for the same secret s, it's generally impossible to compute a valid $d_x(r_x)$ from (one or more) $d_n(r_n)$?
May
2
comment Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?
@HenrickHellström This is a good answer that shows a way to artificially construct H,G,and V that allow for any d to compute a d' so that V(d,r)=V(d',r).
May
2
revised Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?
Merged some suggested changes and made a better rewording.
May
1
comment Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?
I assume that by "valid hash" you mean to run the hash algorithm a second time, yielding an identical digest to a previously computed digest. Right. I believe what you are asking for is if two different messages can yield identical digest values. No, I'm really asking if knowing a digest (and its salt) of a secret, it is possible to compute another digest of the same secret. That is not a collision, since if I know the secret I can calculate a different valid digest for each salt I choose.
May
1
comment Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?
Alright, V(y,s)=1 it's more appropriate.
May
1
awarded  Editor
May
1
revised Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?
added 61 characters in body
May
1
comment Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?
@fgrieu I was assuming (wrongly?) that the salt r can be always be determined by the digest d. For BCrypt implementations known to me this is true, since the digest a string composed by the concatenation of salt and the checksum computed from the secret and the salt. Also, since d=H(s,r), it can be proven that there is a V'(s,r,d)=V(d,s). So if V'(s,r,d)=1 only if H(s,r)=d, also V(d,s)=1 only if H(s,r)=d. I will edit the question if this is confusing.
May
1
awarded  Student
May
1
asked Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?