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bio website github.com/CodesInChaos
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Dec
18
comment What is the difference between CSPRNG and PRNG?
PRNG encompasses all pseudo random number generators, from the horrible rand call in c, over suitable for simulations but not security ones like the mersenne twister, to the most secure cryptographic PRNG. CSPRNGs are simply the subset of PRNGs which are secure. Every stream cipher, including AES-CTR can act as CSPRNG. Depending on the context, one might also include the proper seeding in the scope, which is far more complex than the actual data generation.
Dec
18
comment Why are the lower 3 bits of curve25519/ed25519 secret keys cleared during creation?
The group order is a multiple of 8. Setting the lowest bits zero, sets the scalar to a multiple of 8, ensuring that the points are in the prime-order subgroup without the small subgroup interfering.
Dec
17
comment Calculation of time to crack SHA-256 hash
@JMCF125 Salts are not required to be secret. They should be unique. A username is not ideal since it allows multi target attacks against different versions of the same user's password, or against the same username on different websites. But in the context of this question I'd assume it's unique.
Dec
17
comment RSA exhibits symmetrical properties — is it possible to form a cryptanalytic attack?
FIPS.186-4 is long. You should reference the relevant section(s).
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 measurable proof of works
As an alternative you could use hashcash style proof of work, but with the challenger submitting 100 nonces. That will still have variable runtime, but it will peak around the target value with outliers being very rare.
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 measurable proof of works
If it's no problem that the verifier creates the challenge and can cheat, you can use Rivest's timelock puzzle.
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.