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I am an undergraduate computer science and mathematics student in New Zealand. My fields of interest are computer graphics, in particular the physics of light transport, and to some extent cryptography, as well as programming and software development in general.


Jan
11
awarded  Custodian
Jan
11
reviewed Leave Open Why is RSA usually limited to messages up to 1 block
Jan
10
comment Is it possible to break a hash-based block cipher?
@Polynomial I don't understand your want of using CBC - you don't have a block cipher here, since $n$ depends on the position of the block in the plaintext, as Samuel Neves noted. The first line is a mode of operation in itself. CBC depends on the block cipher being, well, a block cipher: in your case, it is not, using CBC (or any other block cipher mode) would be ill-advised.
Jan
10
comment Is it possible to break a hash-based block cipher?
You'll need an IV somewhere, otherwise you have key reuse issues.
Jan
10
comment What is the progress on the MIT LCS35 Time Capsule Crypto-Puzzle?
If that factors of $n$ are known, you don't even need the CRT. You have enough information to reduce $2^t ~ \text{mod} ~ \varphi{(n)}$ and efficiently solve the puzzle.
Jan
10
comment Why can't I break ElGamal encryption by brute-forcing the secret exponent?
@PaŭloEbermann Good point, since you're iterating them anyway. I went for the parallel approach, since it's embarrassingly parallel.
Jan
8
comment Why is RSA usually limited to messages up to 1 block
If you encrypted the whole thing with RSA, the ciphertext would also be quite a bit larger than the plaintext, because of per-block padding.
Jan
7
comment Why does WPA-PSK not use Diffie-Hellman key exchange?
If you already have shared some secret data (as "pre-shared key mode" seems to imply) then you don't need to perform a public key exchange. You probably just exchange a nonce to agree on the derived encryption key and be on your way.
Jan
7
revised Ideal passphrase length: old diceware method (5 words) vs. your Bitcoin wallet.dat passphrase lenght (8 words) and doubling passwords?
added notes on salting
Jan
7
comment Why can't I break ElGamal encryption by brute-forcing the secret exponent?
In cryptography, we don't generally offer figures, after all we don't know the attacker's capabilities. But when we say "infeasible", we generally mean "beyond the reach of any realistic adversary". But, for all intents and purposes, "not till the end of the universe" is a good approximation.
Jan
7
answered Ideal passphrase length: old diceware method (5 words) vs. your Bitcoin wallet.dat passphrase lenght (8 words) and doubling passwords?
Jan
7
accepted Differential cryptanalysis - breaking the last round of FEAL4?
Jan
7
answered How and why can a decryption program tell me that a key is incorrect?
Jan
6
comment Simple homomorphic crypto for 32-bit integers
One thing that comes to mind is the Pallier cryptosystem, which is additively homomorphic. But I would also be interested in lightweight schemes to achieve this. The small 32-bit space might be a problem for public key schemes, though.
Jan
6
comment Why can't I break ElGamal encryption by brute-forcing the secret exponent?
I think your confusion comes from the illusion that repeated squaring would help find $x$. It does help, to some extent - instead of $O(q^2)$ operations (go over each possible $x$, and naively raise $g$ to that power), you get $O(q \log_2 {q})$ with repeated squaring, which, while better, still doesn't make this possible.
Jan
6
comment Why can't I break ElGamal encryption by brute-forcing the secret exponent?
$x$ is selected at random in $(\mathbb{Z}/q\mathbb{Z})^*$. Typically, $q$ is several hundred bits long. You cannot feasibly iterate through such a large search space in a brute force attempt to locate $x$.
Jan
6
comment Properties of Ideal Straight P-Boxes
You probably also want to add that the P-Boxes need to maximize diffusion across inputs and outputs, to make linear and differential cryptanalysis more difficult. Optimal diffusion = ideal P-Box, I suppose.
Jan
5
comment Does Grover's algorithm effect block size or only key size?
I believe 3DES (or any cipher with a 64-bit block size) in CTR, CFB or OFB mode can be distinguished from a random stream after a few dozen gigabytes of output. Not a problem for most applications, though.
Jan
4
comment How will Cryptography be changed by Quantum Computing?
@mary They are hardly a practical reality, we don't know if it's physically possible to build a sufficiently large quantum computer. But in any case, a small block size allows you to distinguish the output of a block cipher from a random stream, which is a weakness - I suspect Grover's algorithm would also speed up this type of attack, requiring you to increase the block size accordingly as well.
Jan
4
reviewed Reviewed Example Rainbow Table Generation