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visits member for 2 years, 9 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.


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
Feb
10
comment Is there a standard way to extend the output of a hash?
What does OP use for secret? A hash function isn't a PRF. What billpg wants is a construction which takes the fixed-length output of the hash function and stretches it without any secret data (for instance, the variable-length processing Skein uses, which basically runs the Threefish cipher in counter mode using the hash output as a key). One could always use a constant value for secret, but then it's hardly standard.
Feb
10
comment What does the notation $1^n$ stand for?
possible duplicate of What does the expression $1^n$ mean as a function argument? and also of What do $0^n$ and $1^n$ mean in cryptography?
Feb
8
answered Hashing a uuidv4 + time to create a unique id
Feb
7
comment Encrypting a payload for transmission over HTTP. AES256 with PBKDF2
@ndsc Take a look here: security.stackexchange.com/questions/3959/…. Thomas Pornin recommended 20000 rounds as a minimum estimate and that was in 2011, computational power has increased quite a bit since then. PBKDF2 will eventually fall behind on the power curve since it is easily parallelizable, but until bcrypt, scrypt and the likes get better support and become a bit more mainstream it's the most reliable. You have nothing to worry about, though, it was just a side note that your iteration count could be a bit higher, not a weakness.
Feb
7
comment Encrypting a payload for transmission over HTTP. AES256 with PBKDF2
@ndsc Btw 20000 PBKDF2 iterations are a bit on the low side these days. Recommend at least 50k and 100k if possible.
Feb
2
comment The difference between these 4 breaking Cipher techniques?
@hakoja Good point about CPA, forgot about that.
Feb
2
revised The difference between these 4 breaking Cipher techniques?
deleted 221 characters in body
Feb
2
answered The difference between these 4 breaking Cipher techniques?
Jan
27
comment How cryptographically secure was the original WW2 Enigma machine, from a modern viewpoint?
Does the question also assume that the workings of the Enigma machine (all versions) are made available to the cryptanalyst, in accordance with Kerckhoffs's principle?
Jan
27
comment How long will my encryption remain private?
@Christian The point I am making is the fact that the bitcoin protocol makes it harder and harder to mine blocks up to a point where it is no longer possible is a form of planned obsolescence, because it is quite possible that in the future, finding even a partial preimage of SHA-256 will become easier than brute force and the protocol will be broken (a rather major problem for a currency). I'm not an expert in bitcoin and do not claim to be, and was only replying to the question about bitcoin being about finding collisions.
Jan
27
comment How long will my encryption remain private?
@Christian Yes, I should have said (and was adding) that only the mining part has planned obsolescence. The transaction part of bitcoin is another story.
Jan
27
comment How long will my encryption remain private?
@AJMansfield No, only partial preimages afaik, such as "the first X bits of the hash must match this bitstring", which cannot be done efficiently as far as we know, hence the proof-of-work aspect of it (collisions do not matter for that part of bitcoin I believe). If a fast preimage attack on SHA-256 were discovered, bitcoin would be utterly broken, which is why it (or at least the proof of work part of it) has planned obsolescence in a few years were all blocks will have been mined - hopefully before SHA-256 is broken enough to matter.
Jan
26
awarded  Yearling
Jan
25
comment How can I find the prime numbers used in RSA?
To answer this question you need to understand what the private key given in the problem means (what do the two numbers stand for). Once you do the answer should be relatively simple.
Jan
25
revised How can I find the prime numbers used in RSA?
reformatted using code tags
Jan
23
comment Question about SHA-2 (and potentially similar hashing algorithms)
If the constants were not constant, you could not use the hash function without keying it, so it would not be a hash function but something else. You can read up on en.wikipedia.org/wiki/Nothing_up_my_sleeve_number