8,789 reputation
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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 2 years, 9 months
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Oct
4
comment NIST temporarily closed — will that have a negative impact on the future of cryptography?
Avoiding NIST standards just because they come from NIST isn't that useful. We need to understand why they're broken. Without that understanding we can't know if alternatives aren't just as bad.
Oct
4
comment Three-way hash collision
For narrow pipe (or even local wide-pipe) constructions you'll get a four-way hash collision for merely the cost of two normal collisions.
Oct
4
comment Difference between salted hash and keyed hashing?
A key is secret, a salt is not.
Oct
3
comment Extracting only the entropy
@Blaze /dev/random is no good. Its performance sucks. Because for some reason it tries to limit the output to the estimated entropy.
Oct
3
comment Estimating bits of entropy
To properly estimate entropy you need a reasonable model of the underlying physics. And it's rather hard to get right, it's one of the reasons why supposedly secure PRNGs fail.
Oct
3
comment Decrypting a message without the private key using CRT
1) Do the different encrypted messages correspond to the same plaintext? There is an attack if the same message is encryted to e different public keys, but not if those messages are different. 2) Do you use textbook RSA (no secure padding) or real RSA? The attack doesn't work if proper padding is used, since then you will never get identical padded plaintext messages.
Oct
3
revised Specification of the scream stream cipher is unclear
added 4 characters in body; edited title
Oct
3
revised Please punch holes in this authentication scheme
added 21 characters in body
Oct
2
comment how to iteratively calculate a^emod n with modulus n sized 4096 bits
@owlstead I'm not aware of any issues, provided proper padding is used.
Oct
2
revised Attribute-based cryptography
edited tags
Oct
2
comment NIST temporarily closed — will that have a negative impact on the future of cryptography?
At least they didn't shut down their NTP server. That would have been embarrassing.
Oct
2
comment Extracting only the entropy
@D.W. I suspect the real problem is that Blaze wants to limit output to the entropy of the input, similar to /dev/random on linux.
Oct
1
comment Would RSA make sense if we used no computers?
It's not clear if asymmetric encryption would be useful for their use cases, even if we ignore performance.
Oct
1
comment How to calculate y value from ((y*y) mod prime) efficiently
Mathematical routines for the NIST prime elliptic curves describes an algorithm for modular square roots as required by NIST P-224. "Routines 3.2.4, 3.2.5, 3.2.6, and 3.2.7 are all auxilliary to 3.2.8, which is used to compute square roots modulo p 224 . The method is based on an algorithm of Pocklington described in [Ber]." which refers to Bernstein - Faster square roots in annoying finite fields
Oct
1
comment how to iteratively calculate a^emod n with modulus n sized 4096 bits
Accelerating public key operations sees a bit unusual. Typically it's the private key operation that needs acceleration since it's 100x as expensive. If performance of public key operations is really an issue, I'd consider using e=3
Oct
1
comment how to iteratively calculate a^emod n with modulus n sized 4096 bits
You might be able to use CRT together with multi-prime RSA.
Oct
1
comment Hybrid encryption with RSA and AES versus spliting into multiple RSA messages?
@Markus Why don't you simply use TLS with client certificates?
Oct
1
comment Why are cryptography algorithms not exported to certain countries?
1) It's just politicians being behind the times. Of course copying open source crypto is trivial for those countries. 2) For most algorithms it's extremely unlikely that they were backdoored 3) Writing your own implementation is risky. Most crypto code I've seen is broken, even when it builds on standard primitives like AES.
Oct
1
comment Hybrid encryption with RSA and AES versus spliting into multiple RSA messages?
@Markus I don't understand what you're doing, but it's probably a bad idea.
Oct
1
comment Hybrid encryption with RSA and AES versus spliting into multiple RSA messages?
Don't forget to include a MAC, else active attacks will break your scheme. Personally I'd go with NaCl's box operation instead of building my own hybrid encryption scheme.