9,586 reputation
12347
bio website github.com/CodesInChaos
location Frankfurt, Germany
age
visits member for 3 years, 1 month
seen 8 hours ago

Aug
7
comment Allowing the user to choose the hashing formula at the registration
TrueCrypt is funny that way. It allows the user to pick from Whirlpool, SHA-2 and RIPEMD160, but uses far too few iterations of PBKDF2. A decent iteration count (or even scrypt) would have gained far more than the choice of hash function.
Aug
7
comment Allowing the user to choose the hashing formula at the registration
Just choose one secure scheme, such as scrypt with good parameters.
Aug
6
comment Swapping Key and IV in AES? Safe?
At what granularity do you need your irreversibility? 1 byte? 16 bytes? 1 KB? Larger blocks increase performance, but it's possible to go backwards to the beginning of the block.
Aug
6
comment salting with password hash to improve security?
@e-sushi The difference is that you used it as a close reason, whereas I just commented. Linking to similar questions on other se sites is fine, but it's generally not considered a valid close reason.
Aug
5
comment Is AES-XTS considered safe to encrypt multiple files with the same keys?
Encrypting the same plaintext block twice at the same position leads to identical ciphertext block. That's already quite a big leak.
Aug
5
revised Finite fields in elliptic curve
added 405 characters in body
Aug
5
comment salting with password hash to improve security?
Duplicate on security.stackexchange: When hashing passwords, is it ok to use the hashed password as the salt?
Aug
5
answered Finite fields in elliptic curve
Aug
5
comment Discrete log problem with modulus prime
DL is hard for prime moduli as long as $n-1$ has certain properties. We typically use primes for Diffie-Hellman or DSA.
Aug
5
revised Why are there $ signs in my passwd file?
deleted 6 characters in body
Aug
5
comment Why Elliptic curve cryptography are not popular in practice
"RSA [...] can be implemented using the technique of Elliptic curves" Generally you don't implement an RSA equivalent on elliptic curves. I think it doesn't offer a real advantage of normal RSA. Typically we use Diffie-Hellman or DSA (and some very similar algorithms) on elliptic curves.
Aug
5
comment Finite fields in elliptic curve
$a$ needs to be an integer (which can be reduced modulo the curve order). There is no operation that multiplies two curve points, and dividing two curve points is prohibitively expensive (requires computing the discrete logarithm)
Aug
2
revised Different patterns of different paterns, wildcard
edited tags
Aug
2
revised Authenticated encryption mode for stream cipher?
added 29 characters in body
Aug
2
revised Authenticated encryption mode for stream cipher?
added 89 characters in body
Aug
2
answered Authenticated encryption mode for stream cipher?
Aug
2
comment Converting Ed25519 public key to a Curve25519 public key
You can add github.com/nightcracker/ed25519/blob/master/src/key_exchange.c to your project. It should be compatible with the rest of your implementation. It takes an Ed25519 public key, converts it to montgomery, and then computes a scalar multiplication. Don't forget to add a hashing step in the end, preferably one that's compatible with NaCl. That's what I do in my C# port.
Aug
2
comment Converting Ed25519 public key to a Curve25519 public key
In my own application I chose to use Ed25519 public keys in the public API, even for key-exchange. Then convert the public key to montgomery during key-exchange. That's slightly more expensive, but makes the API nicer since there is only one kind of public key visible to the consumer. I also think that it's possible to convert the key-exchange to use Ed25519 natively, removing the performance penalty, but didn't get around to investigating that yet.
Aug
2
revised Converting Ed25519 public key to a Curve25519 public key
deleted 10 characters in body
Aug
2
answered Converting Ed25519 public key to a Curve25519 public key