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Jul
2
comment Is this client-side password hash scheme secure?
Agreed. At a minimum, PBKDF2 should be used to stretch the user-provided passphrase with a random salt, then HDKF can be used for deriving the encryption key and the password verifier (using a different info string for each). Once the verifier is sent to the server, it can simply be hashed once (SHA-2, BLAKE2b, whatever) before being stored.
Jun
26
comment Prime factorization
I can factor $2^n$ for arbitrary $n$. You might want to clarify the question to ask for the factorization of a random semiprime with $p$ and $q$ of a given size.
Jun
25
comment Establishing encryption key using shared secret
Sure it can. Use the PSK to simply authenticate a DH session whose keys are discarded after use.
Jun
25
comment Establishing encryption key using shared secret
This does not provide forward secrecy.
Jun
25
comment Why is HMAC-SHA1 still considered secure?
No, otherwise that would be the advice. SHA-1's collision resistance is only broken in a theoretical sense right now. No known collisions have yet been found, although the current best attack is just on the edge of feasibility.
Jun
25
comment Why is HMAC-SHA1 still considered secure?
It's generally advised to move away ("walk", not "run") from SHA-1. That said, the specific construct of HMAC-SHA1 is still considered safe to use (assuming a secret key) due to the security proof for HMAC which does not rely on collision resistance of the underlying PRF. When in doubt, move to SHA-2.
Jun
19
revised Is secure communication without public-key crytography feasible?
formatting
Jun
19
comment Is secure communication without public-key crytography feasible?
Or simply symmetric crypto? I don't see anything in the question that rules that out.
Jun
19
comment What's the GCM-SHA 256 of a TLS protocol?
Probably answered in this question on the security.SE.
Jun
18
comment 3DES over Galois Counter Mode (GCM) for authenticated encryption
Alternatively, you could use the answer to this question to turn 3DES into a 128-bit block cipher.
Jun
18
revised How can complexity be increased or decreased in AES?
added 372 characters in body
Jun
18
answered How can complexity be increased or decreased in AES?
Jun
17
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Jun
16
revised SHA512 faster than SHA256?
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Jun
16
revised SHA512 faster than SHA256?
added 406 characters in body
Jun
16
comment SHA512 faster than SHA256?
SHA-256 performs 64 rounds of its compression function over 512 bits (its blocks size) at a time. SHA-512 on the other hand performs 80 rounds of the compression function, but over 1024 bits at a time. So yes, SHA-512 performs more calculations in a single invocation, but it does so over a larger quantity of data at a time.
Jun
16
answered SHA512 faster than SHA256?
Jun
15
comment Compression in Symmetric-Encryption?
Compressing can leak far more than that, as evidenced by the CRIME and BREACH attacks against compressed TLS connections.
Jun
11
comment simple algorithm to encrypt/decrypt a text file
Just keep in mind that RC4 is not suitable for production use. It sounds like this is an assignment for a class or something similar, in which case that's not a problem. But it's worth noting.
Jun
5
comment Is the one-time-pad a secure system according to modern definitions?
What? That's not even remotely correct. An attacker, even in a modern context, with the ciphertext and key can recover the plaintext.