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Jan
7
answered What is the keyspace of ROT-13?
Jan
7
comment What is a good way to demonstrate elliptic curve cryptography?
@fkraiem It's silly to encrypt actual messages with ElGamal. Every sane protocol uses some kind of hybrid encryption, such as ECIES. IMO the only reason to use ElGamal encryption is needing its special properties (such as homomorphic encryption).
Jan
7
comment Sophie Germain primes and safe primes
1) Why don't you simply generate a random number of the desired size, check if it's a safe prime and repeat if it's not? 2) I think there are some RFC documents that define standard primes for use with Diffie-Hellman, these are often safeprimes.
Jan
7
comment Are there any Secp256k1 ECDSA test examples available?
Both answers don't include any ECDSA test vectors, only testvectors for scalar multiplication of the base point.
Jan
6
comment NTRU key generation
Where does that 1.5 come from? Is just an arbitrary choice that compensates for multi target attacks?
Jan
6
comment Share encrypted files without giving master key
The standard solution would be to store the random value (which acts similar to an IV) at the beginning of the ciphertext. I would avoid coupling to external meta data, especially since filenames aren't unique.
Jan
6
comment Share encrypted files without giving master key
Why use the filename instead of a random per-file value?
Jan
5
comment How many bits of entropy would I get from 300 coin tosses?
If it's an unbiased coin, you get one bit per toss. Since Shannon entropy is additive for independent events, you get 300 bits total. (This assumes that you toss 300 times, not that you toss 300 indistinguishable coins together)
Jan
4
reviewed Leave Open Why are there no MACs inspired by block cipher modes other than CBC and CFB?
Jan
3
reviewed Close can anyone give the java code to encrypt files using paillier
Jan
3
reviewed Close How will Cryptography be changed by Quantum Computing?
Jan
3
revised C# implementation of curve25519 to ed25519 conversions
added 153 characters in body
Jan
3
revised C# implementation of curve25519 to ed25519 conversions
added 119 characters in body
Jan
3
comment Is BBS used for generation of keys for any modem cryptosystem?
Why do you ask?
Jan
3
answered C# implementation of curve25519 to ed25519 conversions
Jan
3
comment RSA - Why should we sign hash rather than raw content?
The size limitation is similar for encryption and signing. It's the size of the modulus (256 bytes for RSA 2028) minus some space reserved for of padding (40ish bytes). The reason you never heard "we can't encrypt a file bigger than 256 bytes using a RSA public key" is because nobody (competent) does that. RSA encryption is almost always hybrid encryption i.e. you only encrypt a random key with RSA and the rest with symmetric encryption like AES. Just li
Jan
2
comment (Re-)Using deterministic IV in CTR mode / How to: deterministic AES
Since you'll need to publish the IV, it's essential that the derivation function is keyed.
Jan
2
comment Are there cryptographic hash functions which do not have any collisions?
There exist one-way functions which have no collisions, but obviously their output will be at least the size of the input.
Jan
2
comment (Re-)Using deterministic IV in CTR mode / How to: deterministic AES
Search for BEAR, LION, LIONESS. Might be relevant
Jan
2
comment Size of a MAC for a quickly checked message?
I'd use between 8 and 16 bytes, depending on the desired security level.