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Jan
22
answered Use of salt to hash a password
Jan
20
answered How to construct encrypted functions (with either public or private data)?
Jan
20
comment RSA with small exponents?
@owlstead: we use $65537$ mostly out of Tradition. The "attacks" with $e = 3$ are due to the lack of padding, and lack of padding is already a much bigger worry than that: to have an actual weakness due to $e = 3$ (compared to $e = 65537$), you have to thoroughly damage the algorithm (remove the padding step), which creates a bunch of other much bigger weaknesses. With proper padding, no problem with $e = 3$. However, I use $65537$ by default because it avoids questions, and it is not bad either.
Jan
20
comment A simple block cipher based on the SHA-256 hash function
And to say things more generally, that kind of stream cipher is secure only if the stream would be a good PRNG. A PRNG should not allow recomputing its internal state from its output (because knowing the state implies being able to predict subsequent output, and a secure PRNG must offer prediction resistance). It is doable with hash functions, but needs more effort. See NIST SP800-90 for some hash-based PRNG (Hash_DRBG and HMAC_DRBG).
Jan
18
awarded  Nice Answer
Jan
18
comment When to use RSA and when ElGamal asymmetric encryption
@curious: I think you read 99.9% of the books wrong -- quite possibly, the books were unclear. Symmetric cryptography is what you do with the shared key (e.g. AES, HMAC...). DH is how you obtain the shared key (with which you are going to do symmetric cryptography). DH is "asymmetric cryptography" just like, e.g. RSA.
Jan
17
comment When to use RSA and when ElGamal asymmetric encryption
@curious: DH is totally asymmetric cryptography; it is not asymmetric encryption, but it is still cryptography and it is still asymmetric ("asymmetric" = "not all involved party share the same secret keys"). Digital signatures are also asymmetric cryptography (and I do not talk about them here). Also, when you use DH you do not use asymmetric encryption over it. You might have a somewhat skewed idea of what Diffie-Hellman is; I suggest you have a look at the Wikipedia page (unless it is shut off, they seem to want to black it out for a day as a protest against some kind of proposed US law).
Jan
17
answered When to use RSA and when ElGamal asymmetric encryption
Jan
15
answered Can I safely replace XOR with ADD in a stream cipher?
Jan
14
answered How can one securely generate an asymmetric key pair from a short passphrase?
Jan
14
awarded  Enlightened
Jan
14
awarded  Nice Answer
Jan
12
reviewed Approve Two mutually untrusted parties want to exchange data: how to ensure each one gets the data it needs?
Jan
12
revised Compressing EC private keys
typo
Jan
12
comment Compressing EC private keys
@PulpSpy: it might be a gallicism (i.e. a French term which I did not care to translate to English). "Alea" itself is latin for "fate" or "randomness". "Pseudo-alea" means "looks like random bits, but are generated through a deterministic process with an unknown seed".
Jan
12
answered Is it possible to distinguish a securely-encrypted ciphertext from random noise?
Jan
12
answered Compressing EC private keys
Jan
12
answered Two mutually untrusted parties want to exchange data: how to ensure each one gets the data it needs?
Jan
11
comment Does the position of the salt improve its effectiveness when hashing?
@Jim: I am saying position matters in subtle ways for which there cannot exist a simple answer such as "prefix is better than suffix" or the opposite. The only simple answer there is, is: "don't try it at home, it's dangerous".
Jan
11
answered Does the position of the salt improve its effectiveness when hashing?