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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 4 months
seen 12 mins ago

Dec
3
comment Why doesn't this dummy mutual authentication protocol provide mutual authentication?
You can't simply "authenticate". You need to authenticate something. For example a specific message or connection. Else Eve who receives an incoming connection from Alice might simply open a connection to Bob, ask him for [R]B, send that back to Alice, obtaining [R+1]A and send that to Bob. At that point she has authenticated as Alice to Bob and as Bob to Alice.
Dec
3
comment Why doesn't this dummy mutual authentication protocol provide mutual authentication?
Is [R]B the encryption of R using the key B?
Dec
3
comment Why can an RSA signature be authenticated ONLY with the signer's public key?
One way to prevent this is including the public key in the hashed data. I think Thomas Pornin wrote a paper about these issues: Digital Signatures Do Not Guarantee Exclusive Ownership
Dec
3
comment RSA performance
You shouldn't encrypt the message itself with RSA (at least for long messages). Create a random AES key,encrypt message with that key, encrypt AES key with RSA. That way you only pay the much smaller AES cost for the message, and only a single costly RSA encryption.
Dec
3
comment Is the composition of collision resistant hash with non collision resistant hash a collision resistant hash?
Not always, but in practice it will often be even for relatively weak hashes $h_2$. The most important property required of $h_2$ is that preserves at least $2n$ bits of entropy, where $n$ is the target security level. (even that's not sufficient in pathological cases)
Dec
3
reviewed Approve suggested edit on Is the composition of collision resistant hash with non collision resistant hash a collision resistant hash?
Dec
3
reviewed Approve suggested edit on Graphically representing points on Elliptic Curve over finite field
Dec
3
answered IV's from Crypto++ AutoSeededRNG always ends the same: Problem with the PRNG?
Dec
3
reviewed Approve suggested edit on IV's from Crypto++ AutoSeededRNG always ends the same: Problem with the PRNG?
Dec
3
comment Using the same RSA keypair to sign and encrypt
Depends on tricky details of the padding scheme you use and your implementation. It'd generally discouraged to reuse keys like that.
Dec
3
comment What is the chance of a collision when using SHA-3?
1) There is no SHA-3 yet. Keccak has won the competition, but some details haven't been specified. 2) That depends on the output size, which you didn't specify. A hash outputs bytes, not characters. 3) Don't hash passwords with SHA-3. Use bcrypt, scrypt or PBKDF2 4) collisions have little relevance to password hashing, what matters is one-wayness or first pre-image resistance.
Dec
2
reviewed Approve suggested edit on IV's from Crypto++ AutoSeededRNG always ends the same: Problem with the PRNG?
Dec
2
revised Did NIST verify “post-quantum” claims in the SHA3 proposal papers?
added 227 characters in body
Dec
2
answered Did NIST verify “post-quantum” claims in the SHA3 proposal papers?
Dec
2
reviewed Approve suggested edit on Is this encryption scheme perfectly secure?
Dec
2
comment Did NIST verify “post-quantum” claims in the SHA3 proposal papers?
It's ignored because it isn't an attack against the algorithms themselves. It's an attack against the sloppy formulation of security claims in the papers describing those algorithms. Essentially they wrote security claims against classical computers without stating that these only apply to classical computers (which is obvious to any cryptographer). I suspect this is just a product of DJB being pissed that NIST insisted $2^n$ preimage resistance, which cubehash couldn't offer with acceptable performance. Ironically they wanted to lift that requirement after keccak won.
Dec
2
comment What is the function of the secret key “r” in Poly1305?
$r$ being secret is essential. The only point of $s$ is to prevent an attacker from learning $r$.
Nov
30
comment Why is Lamport-Diffie secure?
As far as we know, there there are collision resistant hashes (if necessary we can even weaken that to random prefix collision resistance) which resist quantum computers with slightly larger security parameter.
Nov
29
comment are ideal hashes possible to create?
If your definition of "ideal hash" is that it has no collisions with an input larger than the output, that's impossible. Pigeonhole principle
Nov
28
comment Convert a number to sha-1
I don't get your point regarding collisions. But 2^44 should be feasible as a one-time effort, the rainbow table is only used to make additional conversions cheaper.