1
vote
2answers
53 views

Different padding rules for Merkle-Damgard and Keccak/sponge function

We learned that length padding was used in Merkle-Damgard where after padding with zeros another block is added that contains the initial length of the input. This is supposed to prevent same hash ...
5
votes
1answer
140 views

Is HMAC needed for a SHA-3 based MAC?

HMAC does nested hashing in order to prevent Length Extension Attacks. Given that you use the SHA-3 hash (which is resistant against length extension attacks), would you still need to go through that ...
2
votes
1answer
128 views

Building a stream-cipher out of a hash function?

I've already read this: Is it feasible to build a stream cipher from a cryptographic hash function? However, my proposed construction differs… Suppose the hash generates N bits. These bits are split ...
1
vote
1answer
121 views

Should HMAC or NMAC or plain Keccak be used for a secure MAC?

After some digging around in the HMAC spec I found this (paraphrased): Step 1: If the length of Key equals the block size of the hash function (512 bits/64 Bytes for SHA-256), set the key equal ...
1
vote
1answer
153 views

Hash function and outputs of arbitrary length

I know that Skein can output a digest of arbitrary size, with a kind of counter mode. Blocks of the resulting digest can be computed in parallel. What about Keccak ? I know that a sponge function can ...
13
votes
3answers
697 views

Are NIST's changes to Keccak/SHA-3 problematic?

NIST is working on standardizing SHA-3. They have selected Keccak as the basis for SHA-3, and they plan to make some small changes to it; the result (with NIST's changes) will be standardized as ...
8
votes
1answer
475 views

Why restricting SHA3 to have only two possible capacities?

I just read the presentation slides of John M. Kesley (from NIST) for his invited talk at CHES 2013 about SHA-3 and learned that NIST is going to standardize Keccak with a possibly modified padding ...
4
votes
1answer
155 views

How do you find the inverse degree of a hash function?

I am trying to learn cryptanalysis on the Keccak hash function. One of the papers on zero sum distinguishers talks about Keccak having inverse degree of 3. I am unable to figure this out: how do you ...
6
votes
1answer
299 views

Any point in waiting for the SHA-3 standard?

The Wikipedia article on SHA-3 says that Keccak has been chosen but the standard hasn't been issued. Does this matter? That is, can we just assume it's going to be as specified by the submitters ...
8
votes
2answers
1k views

Why are the constants so simple in Keccak?

Keccak, the construction selected for SHA-3 is very interesting. It seems unlike other primitives and has chosen very simple constants. (Keccak talk PDF) The initial values of the state in Keccak is ...
14
votes
4answers
1k views

What security do Cryptographic Sponges offer against generic quantum attacks?

In the face of non-quantum attacker, Keccak[r=1088,c=512] with 512 bits of output provides: Collision resistance up to $2^{256}$ operations Preimage resistance up to $2^{256}$ operations Second ...