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May
25
comment Finding public exponent e
The Wiener attack implementation that I'm using seems fine up to & including 7FFFFFFF but it will fail after that. Does anybody know modern software that uses 32 bit values for $e$? Otherwise I'll just limit $e$ to 31 bit. I think older software either used $e$ fully random or $e = N$, but a fully random $e$ is impossible to calculate and I've personally never met $e = N$.
May
25
comment Finding public exponent e
@poncho I might not be able to implement this using this description alone, but I'll look into it. I guess that for most keys $e$ is within $1..2^{16} + 1$. I may be able to use Big Step/Little Step for values larger than $2^{16} + 1$ as Wiener's attack seems to eat memory (which is OK for single fire tools, but not so nice if it is part of a library). Maybe this is more a separate answer than a comment?
May
25
comment Finding public exponent e
Performing $m^d (\mod n)$ is much slower on my Java runtime than executing the entire Wiener attack :)
May
25
comment Finding public exponent e
Yep, that's about the gist of it I guess. Would the best way of validating the most used ones to calculate $n$ from $p$ and $q$ and then compare? That seems slow, just performing modular exponentiation seems faster.
May
25
revised Finding public exponent e
added 32 characters in body
May
25
comment Finding public exponent e
@SOJPM Right, that's the problem. I've got $n$ and $d$. Note that $n$ and $d$ are supposed to have been correctly calculated. If I could calculate $p$ and $q$ then my problems would disappear, but $p$ and $q$ calculation from $n$ and $d$ seems to rely on $e$ being available.
May
25
comment Finding public exponent e
yes, I've got some ideas like checking the often used ones first and then check a simple encrypt/decrypt, but I would like the answers not to be influenced by my non-optimal ideas :) And yes, I am aware that this may be hard to do if the public exponent is very large, but this is not commonly the case.
May
25
asked Finding public exponent e
May
25
comment How to calculate RSA CRT parameters from public key and private exponent
You may be interested in this question / answers on SO.
May
25
comment Authenticated EC key exchange without a signing/signature scheme?
Yeah, I guess, the trick is just that it doesn't leak the identity before authentication.
May
24
comment Compacting a substitution cipher key
OK, now it is a random permutation from ${\{0,1\}}^3$ to ${\{0,1\}}^3$, helped you a bit with the edit. I presume any random permutation is allowed.
May
24
revised Compacting a substitution cipher key
added 76 characters in body
May
24
comment Compacting a substitution cipher key
That's not a key, that's a permutation from ${\{0,1}\}^3$ to ${\{0,1\}}^3$. And it is identical to performing XOR with 1 for each bit, also known as a bit complement.
May
24
revised Would this method allow fast authenticated encryption using only a single encryption operation per block?
rolled back to a previous revision
May
24
revised Why is Bcrypt called a Key Derivation Function?
added 8 characters in body
May
24
revised Why is Bcrypt called a Key Derivation Function?
added 318 characters in body
May
24
answered Why is Bcrypt called a Key Derivation Function?
May
24
comment Authenticated EC key exchange without a signing/signature scheme?
If you change PAKE to read PACE then you've got another one - though I haven't compared them yet :)
May
24
revised Why does TLS do Authenticate-then-Encrypt instead of Encrypt-then-Authenticate?
added 58 characters in body
May
24
revised Why do we truncate the hash when using DSA?
added 191 characters in body