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location Wellington, New Zealand
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visits member for 2 years, 7 months
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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
16
comment LFSR for small numbers with large periods
Understood, so you want to switch to a different permutation when the first one is exhausted and so on. Do you have memory requirements? Can you store up to 32 values for a shuffle?
Jan
16
comment LFSR for small numbers with large periods
But a 5-bit pseudorandom permutation always has a period of $2^5 = 32$ (well, excluding the zero, since this is an LSFR). After that a number will repeat due to the pigeonhole principle. This is where I'm confused.
Jan
16
comment LFSR for small numbers with large periods
I see what you mean, but you said "single numbers don't repeat" which would imply you are looking for a pseudorandom permutation of $\mathbb{Z} / 2^5 \mathbb{Z}$ (which can be achieved using a Fisher-Yates shuffle using the 16-bit LSFR). Just truncating off bits wouldn't work here, obviously. Or did I misunderstand you? What you want is, to convert a 16-bit pseudorandom permutation to a 5-bit pseudorandom permutation, am I correct?
Jan
16
comment LFSR for small numbers with large periods
I don't understand the first requirement - why shouldn't those smaller numbers repeat? And since they must not repeat, doesn't this sort of imply the period needs to be reduced to $2^5$ from $2^{16}$, contradicting your second requirement?
Jan
15
reviewed Looks OK Is the One Time Pad (OTP) considered a cryptographic hash function?
Jan
12
reviewed Looks OK Is the One Time Pad (OTP) considered a cryptographic hash function?
Jan
11
comment How and why can a decryption program tell me that a key is incorrect?
Note most symmetric padding schemes will fail to provide integrity with probability $\frac{1}{256}$ in the worst case, so it's really just a sanity check and not a substitute to proper integrity checking.
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?