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Jul
30
reviewed Reject
Jul
30
revised Abstracting primitives and modes of operation
edited tags
Jul
30
comment Assuming a 1024qb quantum computer, how long to brute force 1024bit RSA, 256bit AES and 512bit SHA512
For 3 and 4 it's clearly forever (cost of at least $2^{256}$, and for 2 it's still extremely long (cost of at least $2^{128}$.
Jul
28
comment Security of a 3-party key exchange protocol
@minar One problem with this description is that it doesn't describe what the parties do with the messages they receive. For example if the server validates that $S$ is in the expected place in the message then it can distinguish message 1 from message 3. It's also not clear to me why it'd be a problem if $S$ mixes up $I$ and $R$ since it'd still send them a proper session key. | Analyzing real protocols is certainly much nicer than analyzing underspecified theoretical protocols :)
Jul
28
comment Security of a 3-party key exchange protocol
Can the adversary communicate with S using their own identity E? If you combine that with an unauthenticated stream cipher as encryption you'd get another vulnerability.
Jul
28
comment Security of a 3-party key exchange protocol
What properties does your encryption provide? Is it authenticated encryption? Is it malleable? What about proper IVs?
Jul
28
comment Security of a 3-party key exchange protocol
do you really want k(I,R) in step 3? Or k(R, S)?
Jul
28
reviewed Approve multiparty-computation tag wiki
Jul
28
comment Cryptography used for login and signing transactions
Such short numbers point to symmetric crypto.
Jul
26
revised split up sha256 hash and compare indiv block results
deleted 10 characters in body
Jul
25
reviewed Approve Hash function based on pseudorandom functions and security
Jul
25
comment How random is the shared secret in the Diffie Hellman key agreement
I'm pretty sure that taking the 32 least significant bytes doesn't lead to noticeable entropy loss. Not sure about about the MSB.
Jul
25
comment Generating a secure random number in javascript
@user7676 Depends on the target security level, but somewhere between 100 and 200 bits.
Jul
24
comment What to watch for with openssl generating weak keys? (low entropy)
OpenSSL behaves properly if you use the right PRNG call. The other one is weak and using it doesn't just return bad data, it can also increase the time until the PRNG becomes secure. Unfortunately I forgot how the right call was called.
Jul
24
comment What to watch for with openssl generating weak keys? (low entropy)
The core misunderstanding here is that entropy can be depleted. If you seed a PRNG once, it can churn out practically unlimited amounts of secure pseudo random data. So the only time a good PRNG should block is after startup, until it has acquired 256 bits of entropy, and never after that (perhaps excluding weird events like forks, hibernation, etc.).
Jul
24
comment Ed25519 choice of private key implementation
I don't really get your question. Which different methods are you talking about? if you don't have any special requirements you should simply follow the spec, which derives the private scalar and a second key by hashing a 32 byte seed with SHA-512.
Jul
24
comment Why must we hash lot of times in rainbow tables?
@AbdelouahabPp I think you store the start and end of each chain. Possibly in some implicit form.
Jul
24
comment why hash(hash(str)) is bad?
@AbdelouahabPp If you hash passwords you should use a KDF with many rounds, not few rounds. Fast KDFs are useful if your master key is already strong.
Jul
24
comment Why must we hash lot of times in rainbow tables?
@Abdelou With some tricks you can compare the end of the chain with the hash you want to break so you know if the target hash can be a part of that chain. If it is, you recompute that chain from the beginning checking after each step.
Jul
24
comment Why must we hash lot of times in rainbow tables?
@StephenTouset This question is about hash chains in rainbow tables, a concept that isn't related to making a hash slow.