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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.


Apr
21
comment Is a tweakable block cipher still considered deterministic in nature?
The use of the word "deterministic" in "deterministic algorithm" and "deterministic encryption" is not the same here, be careful not to confuse the two. In the first case is just means that given the same plaintext, key, tweak, and anything else that parameterizes the block cipher, you will always get the same ciphertext (which is obviously true), while the latter is about semantic security. So a tweakable block cipher is still "deterministic" but may be used in probabilistic encryption schemes. Are you asking how to generalize the notion of deterministic encryption to tweakable block ciphers?
Apr
16
comment How can I convert numbers into prime numbers?
@gurghet Again, what advantage does this scheme have over using a PRNG? You can't claim it's "better" without giving any explanation, you should elaborate so future people reading this can understand why.
Apr
16
comment How can I convert numbers into prime numbers?
What is $k$? Why the universal hashing function? I don't see how this is "better" than the standard PRNG method CodesInChaos suggested in the comments.
Apr
10
comment Leak-proof protocol: is such a thing possible?
addendum: except if Alice sends dummy messages to pad the counter, of course, but I'm sure Bob can detect that.
Apr
10
comment Leak-proof protocol: is such a thing possible?
If Alice and Bob can share some more state, and since transmission is 100% reliable anyway, you could keep a counter as IV - you would still achieve semantic security (with a suitable mode of operation) yet Alice would not be able to mess with the IV and inject key material in it. It seems a simpler solution than SIV-CTR, of course it doesn't solve the plaintext malleability issue - I doubt there is a robust solution in that case, since you're basically asking for a way to not allow arbitrary data to be sent over the wire, which Bob cannot distinguish since Alice and Eve share a key.
Apr
7
comment Is it possible to determine or estimate the period for Blum-Micali PRG?
Regarding the last sentence, how exactly did you arrive at the conclusion that the OP wanted to use Blum-Micali? Seems to me he was only curious about the implications of fixed points in the permutation function.
Apr
7
comment Is it possible to determine or estimate the period for Blum-Micali PRG?
Interesting question. The heuristic argument is obvious but I'd be interested in seeing some real (i.e. non-generic) analysis of the properties of $x \mapsto g^x \mod{p}$. Searching for "discrete logarithm fixed point" I found some references, but they all seem to focus on describing the set of primes and primitive roots with at least one fixed point, rather than a lower bound on the number of fixed points for any given $p$.
Apr
7
comment SHA-256 Partial Collision of initial 36 bits and more
Just keep in mind that you're not going to be able to get more than 80 or maybe 90 bits colliding, so don't be disappointed if it becomes prohibitively slow - it's supposed to! But poncho's optimizations should get you most of the way there. Would you care to accept poncho's answer if it helped you, by the way?
Apr
4
comment Is there a technique to confirm that a given large integer value is a product of two primes?
Probabilistic Rabin-Miller is $1-1/4^k$ btw
Mar
28
comment Near preimages, applicable to Bitcoin?
@tylo I think the question was whether cryptanalysis techniques existed to improve upon brute force and thereby defeat the Bitcoin proof-of-work scheme.
Mar
13
comment Would a symmetric cipher with a keylength a big as the data length be information theoretically secure?
@Marste Yes, that is the idea. If this does not apply then I don't think the information-theoretic properties of OTP apply either, and I doubt it applies for AES. But as I said, I am not sure of myself.
Mar
12
comment Would a symmetric cipher with a keylength a big as the data length be information theoretically secure?
I could be way off, though, because I just confused myself. Anyway good question, looking forward to the answers
Mar
12
comment Would a symmetric cipher with a keylength a big as the data length be information theoretically secure?
I don't have a proof but my guts tell me the answer is "no", because it does not seem esufficient that the family of functions $f_k$ used by the generalization of the OTP be all bijective, they also have to satisfy the criteria that $\{ f_k(x) \mid k \in \Sigma \}$ be a permutation of $\Sigma$ for all $x \in \Sigma$ (where $\Sigma$ is the relevant alphabet, e.g. the set of all 256-bit strings). XOR, modular addition and other simple constructs trivially satisfy this through symmetry, but AFAIK it is unknown whether there exist $k_1$, $k_2$ such that $AES_{k_1}(x) = AES_{k_2}(x)$ for some $x$.
Mar
11
comment How to best mix two arbitrary/random n-bit words?
Arbitrary or random? The two are not the same... but if you have two uniform random variables, combining them via any bijective operation produces an equally uniform variable (that could range from a simple XOR to running a cascade of five block ciphers on the variable - the result is the same). So I'm not too sure what you mean, could you clarify?
Mar
10
awarded  Civic Duty
Mar
10
comment Why the same characteristics cannot be used to recover all FEAL4 keys
What are the differentials at the start of round 2 compared to the differentials you started off with? Note the remark about the first subkey being (temporarily) out of reach due to the key whitening step.
Mar
5
comment Long-term data protection, storage of old encrypted traffic and quantum cryptocalipse
I wouldn't be too worried about the "quantum cryptapocalypse", to be honest. Supposedly D-Wave has 512-qubit computers and nobody (there or elsewhere) has even tried to apply the technology to factor a small but not stupidly small semiprime (say, 50-60 bits) as a definitive proof of concept? Come on. I'm not a quantum theoreticist but something smells fishy here. Their excuse of "gearing their work towards optimization problems" is unconvincing, a quantum factorization algorithm that demonstrably works on big inputs would be earth-shattering, much more so than any traveling salesman stuff.
Feb
25
comment Detecting steganography in the stream of short messages
If both the carrier (main stream of bits) and the encryption covering the "steganography" are cryptographically secure, I'm pretty sure you have no way to detect the existence of those messages. In general what happens here is the warden either blocks or corrupts the channel, since the supposed existence of a hidden encrypted stream is impossible to prove or disprove from the data alone. Could you be more specific about the scenario you are describing, because it seems to me that a generic answer won't be very fulfilling?
Feb
15
comment The difference between these 4 breaking Cipher techniques?
@Reid Done, thanks :)
Feb
15
revised The difference between these 4 breaking Cipher techniques?
rearranged attack models