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May
28
reviewed Approve how much trust can we place in protocol verifiers?
May
22
comment One-time pad, zero key and Shannon
By "using Shannon" you mean applying Shannon's theorem? Sure, you can define your key-generation algorithm to pick the all zero key with probability 0 and all others with probability $1/(|\mathcal{M}|-1)$. That's exactly your encryption scheme. Then apply the theorem which states that the scheme is perfectly secret if and only if two condition hold. One of those conditions is that every key is chosen with the same probability, which obviously does not hold.
May
22
comment One-time pad, zero key and Shannon
@CGFoX Well, we are talking about the OTP here (except that the all zero key is not allowed), so by definition, $\mathcal{M}=\mathcal{C}=\{0,1\}^n$. But even if they are some other sets. If the set of keys has an element less that the messages, then for any ciphertext $c$, there exists at least one message $m$ that cannot possibly result in $c$ no matter which key is chosen.
May
21
reviewed Reject Shamir Secret sharing - Can share generator keep x values secret?
May
21
reviewed Reject Shamir Secret sharing - Can share generator keep x values secret?
May
21
revised One-time pad, zero key and Shannon
Added a bit more explanation, why this is a valid argument.
May
21
answered One-time pad, zero key and Shannon
May
21
comment Which concrete applications benefit from Oblivious RAM constructions?
@e-sushi I don't quite get what your comment is trying to convey. He is NOT asking about attacks on ORAM (this is indeed a much used abbreviation). He is asking about the attacks on non oblivious encrypted data-structures that are the motivation to develop ORAM construction (be that Hash based or whatever)
May
21
reviewed Close encryption and decryption time for RSA-crt in java?
May
21
comment Prefix property for variable length pseudo-random generators
$m_0$ and $m_1$ certainly still have to have the same length. Check Definition 3.8. With messages of different length, the security definition becomes meaningless.
May
15
reviewed Reject Is it possible to construct a secure block cipher of size $2n$ given a secure block cipher of size $n$?
May
11
comment The advantages of Merkle Signature and One time Signature
Of course it does: Only a single message can ever be securely signed under the public key of an OTS. In contrast, many messages can be signed under the public key of the Merkle scheme without compromising security.
May
9
reviewed Approve Cryptographically secure keyed rolling hash function
May
6
comment Is G is a secure PRG?
You should specify what F is (I assume a pseudorandom function) and where k comes from.
May
6
revised Is G is a secure PRG?
added 26 characters in body; edited tags
May
4
comment Block cipher encryption of decryption with the same key
It depends on what you mean by "encrypt with a blockcipher". If you mean using a blockcipher in a secure mode of operation, then no, the probability of this happening will be negligible.
May
3
reviewed Leave Closed Is it true, that non-military cryptography appeared in 50's and 60's only thanks to leaks from the NSA?
May
3
comment PRF and hash functions
No, hash functions are only modeled as random oracles for proofs in the random oracle model. If we work in the standard model, a hash function is only assumed to be collision resistant. The key of a hash function stems from a technicality of defining collision resistance. The problem is that it is (almost) impossible to define collision resistance for a single function. Therefore collision resistance is defined for a function family, and the key is required to select a member of that family.
May
2
reviewed Leave Open PRF and hash functions
May
1
answered PRF and hash functions