33,171 reputation
566129
bio website bolet.org/~pornin
location Quebec City, Canada
age 39
visits member for 3 years, 5 months
seen Dec 14 at 14:46

Cryptographer, programmer in several languages (C, Java, several assemblies, Pascal, Forth...). I also have a life.


Oct
23
answered Interpretation of the results of NIST (p)NRG suite
Oct
21
awarded  Nice Answer
Oct
17
answered MD5 update functions
Oct
8
awarded  Enlightened
Oct
8
awarded  Nice Answer
Oct
7
awarded  Nice Answer
Sep
30
awarded  Explainer
Sep
18
comment What is the length of an RSA signature?
That trick can be extended; e.g. you can skip a complete byte (8 bits) if the verifier is ready to compute 256 RSA verifications, while it is trying to guess the missing bits. Maybe more importantly, in ISO/IEC 9796-2, part of the signed data can be embedded "for free" in the signature, so while the signature value has size $n$ bits (or $n-1$ with the trick you describe), the overhead implied by the presence of the signature can be substantially smaller, depending on the situation.
Sep
7
awarded  Good Answer
Sep
5
awarded  Nice Answer
Aug
26
awarded  Enlightened
Aug
26
awarded  Nice Answer
Aug
25
comment Efficiently map $2^n$ unique 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$?
If all possible inputs are known a priori then you can put 64 million entries into exactly 64 million buckets with no collision -- but the mapping will have to know the 64 million entries. And the gist of my answer is that this cannot, in general, be done without using enough ROM or RAM to actually encode the 64 million possible values one way or another.
Aug
23
answered Efficiently map $2^n$ unique 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$?
Aug
18
awarded  Enlightened
Aug
18
awarded  Nice Answer
Aug
14
answered Why can't you decrypt an encrypted message with just the public key?
Aug
13
awarded  Nice Answer
Aug
13
answered How is SHA1 different from MD5?
Aug
12
comment linear computations over bilinear pairings
Two elements in a group are opposite to each other if their product is 1 (or their sum is 0, if you use an additive notation for the group).