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visits member for 2 years, 11 months
seen May 9 at 0:59

Sep
18
accepted What is Identity-Based Encryption (IBE) and why is it “better”?
Sep
18
answered How do I apply differential cryptanalysis to a block cipher?
Sep
18
asked Converting a stream cipher into a block cipher
Sep
18
asked How to forge Schnorr signatures if you can guess the challenge
Sep
16
answered Understanding CRC
Sep
16
asked What is Identity-Based Encryption (IBE) and why is it “better”?
Sep
16
accepted Can I select a large random prime using this procedure?
Sep
15
asked Can I select a large random prime using this procedure?
Sep
15
answered UMAC: to what extent is it in use today?
Sep
10
answered How do I construct a 256-bit hash function from 128-bit AES?
Sep
6
awarded  Teacher
Sep
4
comment Is modern encryption needlessly complicated?
Modern crypto is needlessly complicated; but not because of the (simple) primitives like RSA, DES, and AES. It's universality composability and ZKPs that are the problem.
Sep
4
answered Is modern encryption needlessly complicated?
Sep
2
comment What is the sign bit for in Feige-Fiat-Shamir?
In HAC, 10.26 step b (p. 410) the authors claim that the sign is required to avoid leaking information. I can only guess that this information is the fact that $I_j$ is a square, which seems to not really be very useful (after all, you can't take the square root!). A simulator could produce this same distribution, right? Just generate a random square.
Sep
2
comment What is the sign bit for in Feige-Fiat-Shamir?
Hm, I'd never heard of "unrestricted input" ZK before. But in the excerpt you quoted above, FFS say that we must have our $I_j$ range over all Jacobi symbol +1 values for ZKPs of knowledge. They don't mention "unrestricted input" (perhaps they have some definition of ZK that requires it I guess).
Sep
2
awarded  Commentator
Sep
2
comment What is the sign bit for in Feige-Fiat-Shamir?
It's more than this. The FFS scheme equiprobably multiplies each $1/S_i^2$ by -1 or 1. Since -1 is a non-square with Jacobi symbol 1 (because $n$ is a Blum integer), this preserves the Jacobi symbol while expanding the range of values produced. I don't know why they do this (and the wikipedia version doesn't do it at all).
Sep
1
revised What is the sign bit for in Feige-Fiat-Shamir?
added 26 characters in body
Sep
1
comment What is the sign bit for in Feige-Fiat-Shamir?
The section you cite seems to be a (slightly) different scheme from the one cited in wikipedia (the wikipedia entry doesn't even contain the $I_j$'s; I wonder if it's correct?!)
Sep
1
revised What is the sign bit for in Feige-Fiat-Shamir?
edited tags