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Jan
13
comment What is difference between meet in the middle attack and man in the middle attack?
I don't think that meet-in-the-middle necessarily involves a space-time trade-off. For example collision finding or computing ECDLP require little memory yet are a meet-in-the-middle attack.
Jan
13
comment Difference between AES CMAC and AES HMAC?
Where did you read about AES HMAC? Perhaps you misunderstood and the source was talking about authenticated encryption that encrypts using AES (e.g. in CTR mode) and adds HMAC-SHA-* for integrity?
Jan
12
comment Faster alternative to HKDF
You're creating millions of subkeys per second? Could you elaborate a bit more on the use case and context? Is the master key fixed or different each time? How long are the derived keys?
Jan
12
comment What is the canonical way of creating merkle tree branches?
That depends on how you construct and balance the tree. For simple trees the size determines the structure and you'd only need to give the index of the leaf node to know which path leads to the root.
Jan
11
comment Encryption used in a commercial software product
c[i] = p[i] xor key[i mod 10]. Using xor is a common choice for synchronous stream ciphers‌​. A repeated key is used by the Vigenère cipher, though it's traditionally used with character-wise modular addition instead of bit-wise xor.
Jan
10
comment Elliptic ElGamal Public Key Cryptosystem doubt
@poncho That sounds like a notation issue to me. Since $4^2 \equiv 3 \pmod{13}$ using $\sqrt{3}=4$ sounds reasonable (defining positive as square). $(6, \pm 4)$ is on the curve.
Jan
6
comment Proof that perfect privacy implies that the number of keys is at least the number of messages
You can use MathJax, which is based on LaTeX, by enclosing formulas between $ signs.
Jan
6
comment Is IPsec IND-CCA secure provided the used block cipher is a pseudorandom function?
But why are you mentioning CBC mode then, which is not compatible with PRFs? The proper model for a block cipher is a (strong) PRP. Since PRPs can approximate PRFs up to the birthday bound we can use PRPs even in PRF assuming modes like CTR.
Jan
6
comment Is IPsec IND-CCA secure provided the used block cipher is a pseudorandom function?
Did you mean pseudo-random-permutation?
Jan
5
comment Could an HMAC be used as a hash?
Related question: Why is HMAC-SHA1 still considered secure?
Jan
4
comment Importance of random number generation in Schnorr's signature
@MaartenBodewes Adam Langley patched OpenSSL to work like that since deterministic signatures would have been a breaking change.
Jan
4
comment Importance of random number generation in Schnorr's signature
If you want deterministic nonces, take a look at Ed25519 or RFC6979 - Deterministic Usage of the Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA)
Jan
4
comment How does RSA compute such enormous numbers?
@smrt28 Normally the edit history would show if the post has been edited and by whom. But apparently the history has been lost due to the migration from security.se.
Jan
4
comment Is there a simple hash function that one can compute without a computer?
The linked RC4-Hash is broken: Collisions for RC4-Hash - Sebastiaan Indesteege, Bart Preneel. The paper even includes example collisions.
Jan
4
comment Is there a simple hash function that one can compute without a computer?
Are you suggesting using the message as RC4 key? How are you handing messages with length >256 bytes? What about the trivial collision between a and aa?
Dec
30
comment Why does NaCl's crypto_auth have twice the security level of crypto_onetimeauth?
HMAC can be safely truncated if you want a short auth tag, but I'd avoid truncating Poly1305.
Dec
29
comment When/why is RSA (hybrid) encryption used rather than alternatives?
IES is pretty new compared to PGP
Dec
26
comment Is secp256r1 more secure than secp256k1?
Secp256k1 is over a prime field as well, but has an endomorphism similar to Koblitz curves.
Dec
23
comment How do I get the equivalent strength of an ECC key?
It might be a good idea to pull out $n$ from the equation, so you end up with something like $\frac{l}{2} - 0.17$.
Dec
23
comment What is the best current way to cryptographically secure databases?
What kind of API should the server offer to clients? Do clients download a copy of the database and perform operations locally, with the server only helping with synchronization?