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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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Jan
7
comment Why does WPA-PSK not use Diffie-Hellman key exchange?
They only have a weak long term secret in common. Those aren't good keys for encryption.
Jan
7
comment Why does WPA-PSK not use Diffie-Hellman key exchange?
@Thomas I disagree for several reasons. 1) Password entropy is often low, so using them only for authentication and not for confidentiality seems appropriate 2) Forward secrecy 3) All users who share a WiFi network can read each other's traffic. With a well constructed protocol an attack would have to be active, and one might even bind to the access spot's key, giving a warning when it changes.
Jan
6
revised Why xor the message into the state for sponge hashes?
added 197 characters in body
Jan
6
comment Why xor the message into the state for sponge hashes?
Keccak alternates an unkeyed permutation of the state and injecting the message into the state. Injecting into the state means xor-ing the message block with part of the state. If you change "xor" to "replace" with no further changes the new hash would be just as secure as Keccak regarding collisions and pre-images.
Jan
6
comment Why xor the message into the state for sponge hashes?
@IlmariKaronen "if the remaining part of the state is long enough, that might not matter" If it's not long enough, you're already doomed since in many cases(collision, preimage,...) the attacker can trivially cancel out the existing state. | "how you're going to mix the part you just replaced with the rest of the state" The same way you mix the xor-ed part of the state with the rest of the state. | For hashing where the attacker knows the whole message, replacing vs. xor-ing obviously makes no difference at all. But there are some subtle differences if some part of the message is secret.
Jan
6
revised Why xor the message into the state for sponge hashes?
added 136 characters in body
Jan
6
asked Why xor the message into the state for sponge hashes?
Jan
5
comment RSA 4096 bit key benchmark
@owlstead Personally I like Curve25519/Ed25519 a lot. Quite fast, no timing attacks, compressed points(no validation required) and no random numbers for signing. It's no NIST standard, but that doesn't matter for my personal projects.
Jan
4
comment Does Grover's algorithm effect block size or only key size?
What do you mean by "protocol size"?
Jan
4
revised Calculating RSA private exponent when given public exponent and the modulus factors using extended euclid
edited title
Jan
4
comment Does Grover's algorithm effect block size or only key size?
1) I don't see that paper mentioning Rijndael with 256 bit blocks at all. It talks about AES with 128 bit blocks. AES-256 has a 256 bit key and 128 bit blocks. 2) Summarizing the paper as "AES-256 is not secure" is highly misleading. Related key attacks are irrelevant for pretty much every protocol that uses AES. 3) "Grover [...] cracking symmetric keys 2x faster" That's wrong too. A 2x speedup would be completely harmless. Grover halves the effective key-length, which is an exponential speedup.
Jan
3
comment Calculating RSA private exponent when given public exponent and the modulus factors using extended euclid
Check the "Computing a multiplicative inverse in a finite field" section of the "Extended Euclidean algorithm" wikipedia article.
Jan
3
awarded  Enlightened
Jan
2
revised How will Cryptography be changed by Quantum Computing?
formatting
Jan
1
comment Determining the algorithm used to generate a digital signature
I'd try throwing some kind of ASN1 parser at the signature.
Dec
30
answered Difference between symmetric and asymmetric hash function?
Dec
30
comment Difference between symmetric and asymmetric hash function?
That isn't about asymmetric hashes, but about asynchronous implementations of symmetric hashes. The code doesn't contain the word asymmetric anywhere. | Async in that context means that you order some computation, then do something else, and once the computation is finished(probably on another thread) you receive the result.
Dec
30
comment Difference between symmetric and asymmetric hash function?
There is symmetric(AES) and asymmetric(RSA) encryption. And there is symmetric authentication(MAC) and asymmetric authentication(RSA signatures). Many authentication schemes use hashes, but they aren't hashes.
Dec
30
comment Difference between symmetric and asymmetric hash function?
Can you provide some source for that claim? I've never heard of asymmetric hash functions. Hashes like SHA-x are unkeyed and symmetric.
Dec
30
comment Is RSASSA-PKCS1-v1_5 a good signature scheme for new systems?
It's important to note that PSS isn't broken when used without randomness, the security reduction just becomes less tight.