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Dec
17
comment Diffie-Hellman on additive group
But if you use addition modulo a prime, that's a bad idea, since the discrete logarithm problem in that group is easy.
Dec
17
comment Diffie-Hellman on additive group
Additive vs. multiplicative is only a difference in notation. Replace multiplication with addition and exponentiation with scalar multiplication.
Dec
17
revised Diffie-Hellman on additive group
added 6 characters in body; edited title
Dec
17
comment Calculation of time to crack SHA-256 hash
Since you're using a salt (the username), multi-target attacks don't work and thus it doesn't matter if there are one or one million hashes in the db.
Dec
16
comment Is AES still secure considering all this NSA/Snowden scandal?
Related question: AES timing attacks
Dec
16
comment Is AES still secure considering all this NSA/Snowden scandal?
It is possible to implement constant time AES. Either using the AES-NI instructions (extremely fast) or using bitslicing. For parallelizable modes like CTR, bitslicing is relatively fast. Those constant time implementations are gaining popularity, but are still in the minority.
Dec
16
comment Combining two hashing functions
As far as non cryptographic uses are concerned, a cryptographic hash is a perfect.
Dec
15
comment Are IVs and salts the same and usable for each other uses?
If you use a new PBKDF2 salt for each message, you don't need an IV for the actual cipher. But an IV for the cipher can't offer everything you gain from salting PBKDF2. But often it's useful to not compute PBKDF2 per message, in which case a per message IV is needed again.
Dec
15
comment Different between Shared Key and Common Key in DLP Application
Please cite examples of the usage of each term. I don't recall any paper using "common key", but in the context of diffie-hellman it's likely that it means the same as shared key.
Dec
15
comment Difference between implicit signature and explicit signature
What exactly do you mean by an implicit signature? I couldn't find a good definition.
Dec
15
comment Game traffic encryption AES CTR + HMAC
@Reid GCM needs 16 byte tags. If you truncate the tag, its security crumbles.
Dec
15
comment Game traffic encryption AES CTR + HMAC
Your main problem is that you don't want security, only obfuscation. Any moderately talented reverser will be able to extract the AES key with standard AES implementations.
Dec
13
comment Generate random in secure message transfer
don't use nanoTime
Dec
13
comment When do I need to renew keys for Salsa20 or HMAC?
Key renewal is useful for forward secrecy or recovery from key compromise.
Dec
13
comment When do I need to renew keys for Salsa20 or HMAC?
Letting the Salsa20 counter roll over would be a fatal flaw, but I doubt you'll be willing to wait for it (It'd take around 10000 years with typical computers).
Dec
13
comment So what is quantum cryptography anyway?
The track record of QKD is pretty bad for something "perfectly secure". It's just that many implementations are flawed, just like implementation of traditional crypto is a far bigger threat than traditional crypto itself.
Dec
13
revised Public-key cryptosystems without poly-time quantum attacks
edited tags
Dec
13
revised Did NIST verify “post-quantum” claims in the SHA3 proposal papers?
edited tags
Dec
13
comment So what is quantum cryptography anyway?
Nothing is wrong with traditional symmetric crypto. The popular asymmetric schemes (RSA, DH, Elliptic curves) will be broken by large quantum computers, but we have alternatives (McElise, NTRU,...) which are believed to resist quantum computers. => IMO quantum crypto is useless
Dec
11
comment Do test vectors ensure a cipher is free of backdoors?
Use code review and test vectors. But even if you do a bug may slip by. For example there were recent bugs in popular GCM which caused a total security breakdown for certain message lengths.