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Aug
24
reviewed Close Is double encryption using AES using different key lengths (128 bit and then 256 bit) vulnerable?
Aug
24
reviewed Leave Open How to build a secure cryptographic algorithm
Aug
24
reviewed Leave Open What is the difference between a random oracle and a probabilistic algorithm?
Aug
24
comment Possible to determine equivalence of hash codes from different hashing functions?
@P.Anderson: I was thinking about two different approaches; one just did the same approach, but using Whitebox cryptography. The other approach was to use public key crypto; one approach (extending the comparison function to include the $i, j$ values) would be to define an RSA modulus $m$ with secret factorization, and $H_i(x) = SHA256(x)^ i \bmod m$ (with obvious restrictions on the $i$ values), and defining $F(M_i, i, M_j, j) = (M_i^j == M_j^i) \bmod m$
Aug
24
comment How many bits to flip in an RSA public key to do signature forgery?
@dannycrane: In that clause, I was assuming that the public exponent $e=3$. A simple calculation (and substituting in the value of $e$) gives $2.89 \times 1/(3-1) \approx 1.44$
Aug
24
comment How feasible would it be to generate 300 million public key pairs in 8 hours?
@fgrieu: One reason this may come up is if you're trying to generate an RSA private/public key where the public key has a specific fingerprint.
Aug
23
answered How feasible would it be to generate 300 million public key pairs in 8 hours?
Aug
22
answered How can you produce visual cryptography?
Aug
22
comment How can you produce visual cryptography?
Actually, I believe that the combination function used in the example is AND, not XOR. That is, the pixel in the final image is white only if the pixels in both the original images is white. That said, it turns out the generation process still (mostly) works (!)
Aug
22
answered Possible to determine equivalence of hash codes from different hashing functions?
Aug
21
comment Probability of $D_k(a*k+b) =p$ for a PRP
What's $p$? Is that another free choice, or is it a fixed value? Also, is $*$ multiplication mod $2^{128}$? Or, is it multiplication in some representation of $GF(2^{128})$?
Aug
20
reviewed No Action Needed Is entropy being lost when the hash of a secret has a specific format?
Aug
19
answered Is full Homomorphic encryption quantum resistant?
Aug
19
reviewed No Action Needed variant of Diffie–Hellman key exchange protocol
Aug
19
reviewed No Action Needed File encryption with AES CTR mode
Aug
18
comment Usage of Zero-knowledge proofs for NP-complete languages
If you had a PPT algorithm that could find a coloring in a graph with nonnegligible probability, then you can likely use it to break AES (or RSA or EC); to find the setting of key bit i, generate two SAT instances, one with a solution if the bit is 0, and one with a solution if the bit is 1; convert those into G3C problems and hand both to your PPT algorithm. If it finds a coloring in one of them, then you know that bit setting. Because of this nonrigorous argument, it appears unlikely that any such algorithm exists (assuming $P \ne NP$)
Aug
18
comment Would the encryption of bigrams and trigrams weaken the code?
Obvious question: suppose that 'th' was one of your frequent bigrams; then suppose you encrypt the three character plaintext string 'sup' as the two letters 't' 'h' and the bigram 'th'. How would the decryptor then know that the ciphertext 'thth' consisted of three symbols 't', 'h', 'th', and not any of the other 3 ways to lex it?
Aug
18
comment Is calculating HMAC from hashed input a good idea?
It comes down to what the question is. Is it "would doing HMAC(K, H(M)) yield any practical attacks", or "might there be academic attacks on HMAC(K, H(M)) that would be easier than HMAC(K, M)?"
Aug
18
answered Is calculating HMAC from hashed input a good idea?
Aug
17
awarded  Nice Answer