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visits member for 2 years, 2 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.


Nov
16
comment Are there any bijective one-way functions not based on number-theoretic hardness assumptions?
@SDL "hard to compute" has a specific meaning in cryptography (and as you probably guessed, it happens to mean "infeasible"). Maybe you should detail exactly what your requirements are in your question in unambiguous terms.
Nov
2
comment Is there an algorithm or hardware that can sign/verify natural time?
I guess the assumption was that time remained linear. Obviously if you can manipulate time through the laws of physics all bets are off... damn physics, always telling us "yes, but..." :p
Nov
1
comment Does ssl_rsa_with_rc4_128_md5 have known weaknesses?
@hunter Right.$\left . \right .$
Oct
31
comment Does ssl_rsa_with_rc4_128_md5 have known weaknesses?
It's unclear what you're asking. Secure with respect to what? Besides, the question is rather vague, and invites speculation - simply "using" a good cipher doesn't mean you are instantly and utterly protected, just like purchasing a bullet-proof vest won't protect you unless you wear it correctly.
Oct
21
comment Estimating random number entropy for input into 256 bit hash
@liquin Yes, that is correct, and, yes, that is correct. You would reject values 8 and 9 and try a new number until you get a value between 0 and 7 (which you interpret as three bits). The problem is the algorithm only works well if you have a large number of such numbers (preferably infinitely many) since you are probabilistically rejecting some of them. And to be fair using SHA-256 is probably the safest option, unless you have some requirements you have not told us about.
Oct
21
comment Estimating random number entropy for input into 256 bit hash
The last three bits are NOT uniformly distributed. 000 and 001 appear twice whereas the others appear only once. If you use these directly to build up a 256-bit bitstring you have a weakness. Either feed them into SHA-256, assuming around (but not exactly) 3 bits of entropy per number (you can calculate the exact entropy with Shannon's entropy equation) and collect the final digest when you've reached 256 bits of input entropy, or use rejection sampling to correctly extract uniformly distributed bits from a stream of such 0-9 numbers, assuming you have enough of them to avoid running out.
Oct
18
comment Selective format-compliant JPEG encryption?
You can encode data in the alpha channel for most photographs which don't use that channel (if the format permits it), which lets you introduce some redundancy, maybe saving the scheme. You can also insert encrypted metadata in most formats without breaking compliance, which may or may not be compressed. So I'm not too satisfied with this answer. There is more to it than just "you can't do it because there's not enough space". There is plenty of space in many image file formats to write a bunch of stuff (though obviously it will be very file-format-centric, not a general solution).
Oct
17
comment How exactly was the finalist chosen in the NIST AES competition?
Obviously the AES-NI instructions did not exist before AES was standardized, though it certainly helps performance a lot.
Oct
17
comment How exactly was the finalist chosen in the NIST AES competition?
I hope by implementation difficulty they really mean ease of implementation....
Oct
16
revised RSA Proof - di-mgt - modulo properties
fixed typo in formula
Oct
14
comment Encoding numbers that can be decoded mentally?
@RichieFrame Good luck converting to hexadecimal mentally.. you might as well use the substitution cipher directly on the decimal digits. Test: how advanced are the adversary's capabilities? Have you got a concrete threat model to go on? If you're talking about a random person seeing some numbers and trying to make sense of them on the fly, this is where security through obscurity might be more cost-effective (e.g. interleave the digits, then increment each digit by a constant you remember, modulo 10, etc..). But for anything more permanent you'll need something better.
Oct
7
comment How do we prove that AES, DES etc. are secure?
The first sentence is problematic, Luby-Rackoff is a block cipher construction proven computationally secure under certain assumptions, but it doesn't have a key as long as the message. I think you went to say something else and forgot to update the sentence.
Oct
3
comment Can an RSA private key have several public keys?
Plus, if you do that and someone gets hold of two public keys, he can take the difference and get hold of a multiple of $\varphi{(N)}$, and, well, game over.
Oct
2
comment NIST temporarily closed — will that have a negative impact on the future of cryptography?
I would be worried if it had shut down permanently, but given that it will likely reopen in less than a month, I don't think there is much to worry about. But I would be interested in reading different perspectives on the matter.
Sep
27
comment High throughput and efficient data encryption/description? (other than AES)
I don't think any block cipher implemented in software can really compete with a hardware-accelerated implementation. And since AFAIK AES is the only cipher which has hardware implementations in consumer processors... otherwise Threefish is pretty fast on modern 64-bit processors, clocking at just over 6 cpb which is rather competitive (but there are yet faster ciphers). And it is not a standard cipher, even though "Bruce made it" :p
Sep
25
comment Algorithm for sharing secret information with redundant keys
This scheme is called, surprisingly enough, "secret sharing". Have you tried googling "secret sharing software"? I am getting at least 4 promising hits on the first page, have you explored these? Also, software requests are off-topic on this site.
Sep
24
comment How broken is a xor of two LCGs?
@RobinHouston Alas, the difficulty of the cryptanalysis doesn't increase proportional to the complexity of the cipher. Thanks for the edit - if noboby has produced a break before the weekend I'll give it a try (not much time for crypto during the week)
Sep
24
comment How broken is a xor of two LCGs?
This will probably require some form of linear cryptanalysis to produce a state recovery attack. The high bit is biased as fgrieu notes but after some empirical research last night I did not find any trivial flaws to exploit with this modulus $p$. Barring the MSB, I am thinking a distinguisher could maybe be constructed somehow by using the lattice structure of LCG's, but this question is far from trivial.
Sep
22
reviewed Needs Improvement Relationship between Elliptic Curve Discrete Log, Integer Discrete Log, and Integer Factorization
Sep
22
reviewed Satisfactory How to supply the GCM authentication tag to the OpenSSL command line tools?