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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 5 months
seen 6 hours ago

Nov
7
comment What is the value of Q such that Q|P-1 where P is a prime number?
Assuming this is about generating a finite field with a subgroup of order Q, we usually choose Q first, then choose a r such that P=Q*r+1 with P of appropriate size. Repeat with different Q or r until P is prime. That way you don't need to do any factoring. For Diffie-Hellman we often choose r=2 and vary Q, for signatures fixing Q and varying r can be preferable.
Nov
7
revised Crypto-Compression Algorithms?
added 518 characters in body
Nov
5
comment What is more secure, a ciphertext encrypted with AES-256 or encrypted with 3 different AES-128 keys?
Your title says 3 AES-128 keys, the body says 2. Which one are you talking about?
Nov
4
comment Square roots, prime factorization
Since the OP has now solved the problem, I encourage you to turn the hint into a proper answer that describes the whole solution.
Nov
4
comment Can DH_anon really be exploited by an attacker?
A client that allows anon DH is still vulnerable to MitM with anon DH even if the server disabled it. (unless perhaps it does something unusual like client certificates or other cryptographic authentication)
Nov
4
answered Can DH_anon really be exploited by an attacker?
Nov
4
comment RC4 encryption/ decryption with hashing
Why new code based on RC4 in 2014? There is a lot of work on getting rid of RC4 because it's potentially weak.
Nov
3
reviewed Approve Showing that $2^{N-1}\equiv1\pmod N$ when $N=2^p-1$ for prime $p$
Nov
3
awarded  Popular Question
Oct
31
comment RSA Decryption given n, e, and phi(n)
1) If there are errors in your first answer, edit it to correct it, instead of posting a new one. 2) I recommend including the essential parts of your code in the answer. An answer in stackexchange should be able to stand on its own, without external resources that might disappear over time.
Oct
30
comment RSA Decryption given n, e, and phi(n)
Use a big integer library, most programming languages either contain one (at least C# and Python do) or have a readily available third party implementation. (unfortunately the wolfram alpha link above doesn't work, it truncated phi)
Oct
30
comment RSA Decryption given n, e, and phi(n)
1) Compute d as the Modular multiplicative inverse of e, i.e. $d=e^-1 \bmod \phi(n)$ using extended euclidean 2) compute $m=c^d \bmod n$
Oct
30
revised Stream Cipher : Never use stream cipher key more than once
added 6 characters in body; edited tags
Oct
30
comment Why develop new stream ciphers when block ciphers can be trivally made into streams?
Comparing dissimilar ciphers like AES and RC4 is pretty difficult. On large modern CPUs AES will be much faster.
Oct
30
comment What are these twist attacks with cost $2^{58.4}$ on NIST P-224 curve, and when do they apply?
Bernstein likes doing ECDH using x-only ladders without first verifying if the given x value is on the curve or the twist. For example the Curve25519 implementation in NaCl works like that.
Oct
30
comment Why is it hard to calculate Logarithm on Diffie Hellman?
You compute $g^x \bmod p$ via square-and-multiply in time $(\log(p))^3$, which is feasible for a 1000 bit $p$. The naive algorithms you describe are far too expensive.
Oct
30
comment Are there any digital signature algorithms in common use that result in 32-byte signatures?
There is a less common scheme called BLS, which produces 32 byte signatures at a 128 bit security level.
Oct
30
comment Are there any digital signature algorithms in common use that result in 32-byte signatures?
Modifying an ECC signing lib, especially if it's already Schnorr based like Ed25519, to use hashed Schnorr at a size of 3x security level isn't that hard. Not sure how this interacts with multi-target attacks though.
Oct
30
comment Low exponent attack against RSA
You shouldn't rely on secret RSA moduli: Hans-Joachim Knobloch - Breaking Public Keys - How to Determine an Unknown RSA Public Modulus.
Oct
30
comment Are there cryptographic hash functions that can be computed using only paper and pen without leaking any information about the plaintext?
Is there a textual description of this hash function? I don't want to watch an hour long video for something that almost certainly doesn't meet the requirements of the OP. Learning to keep 60+ bits in mind at the same time is probably possible, but certainly takes quite a bit of effort.