Henrick Hellström
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 Jan 27 comment Can I use a one time pad key twice with random plaintext? a xor b || a xor c = b xor a || c xor a. The entropy is exactly the same. Jan 16 comment Is it safe to use XOR to encrypt data key using master key crypto.stackexchange.com/questions/2264/… Jan 11 comment Encryption used in a commercial software product Your question is off-topic here. I suggest that you ask this question to the software manufacturer directly. Jan 6 comment Protocol to identify zone of potential agreement without revealing reservation prices and having to trust third parties? A somewhat related problem would be how to eliminate the risk of collusion. Suppose A is working with C, who is the "real" prospective buyer from B. A proposes a maximum price that is lower than what C is prepared to pay, and communicates the result to C, before C and B executes the protocol. This way C is able to start the negotiation with an offer that leads to a final price that is closer to B's minimum. Jan 3 comment Is CPU timing jitter a usable entropy source? I've been using CPU timing jitter as entropy source on a wide variety of CPU models since 2001. Perhaps the most important observation is that it has become more risky on modern multicore CPUs. If you are not careful, you might end up harvesting entropy from a core that is not used for anything else, meaning you will either end up with a poor entropy source, or be stuck in an endless loop. Jan 2 comment Homemade Randomized RSA Suppose you take a guess at $m$. Will you be able to tell if $(A,B)$ is an encryption of $m$ or not? (You will.) Dec 28 comment Shamir's Secret Scheme : Knowing the threshold @IlmariKaronen I understand, but shouldn't the fact that we are dealing with polynomials and not random functions affect that probability? Dec 28 comment Shamir's Secret Scheme : Knowing the threshold @IlmariKaronen Are you sure the probability is exactly $1/q$? I agree with the approximation, but would presume that two polynomials of degree $k+1$ and $t-1$, with $k+1 < t-1$, might intersect in up to $t-1$ different points; not $k+1$ points. Dec 14 comment Cost of attack on DSA with attack on DLP You can't "optimize" Pollard Rho. It is what it is. You can however (a) modify the algorithm to use various trade-offs, or (b) optimize the implementations of the underlying arithmetic operations. In the former case you will get a different algorithms. which might or might not be faster depending on a lot of factors. In the latter case you might get a speed up by a constant factor. Dec 5 comment Unconditionally Secure Authentication Do I understand correctly that you are looking for a MAC that will not leak information about the plain text, even in the face of an unbounded attacker (simple: EtA will work)? Nov 28 comment RSA: Most significant key bit always 1? @pafodie There is a subtle difference between numbers and bit strings. Bit strings might have either 0 or 1 at the most significant index. All positive non-zero numbers will always have 1 in the most significant bit. Nov 26 comment Does the RSA algorithm use repeated squaring? The RSA algorithm doesn't use repeated squaring. However, many implementations of the RSA private key operation do use implementations of modular exponentiation that do use repeated squaring in one form or another. Nov 21 comment CTR DRBG dependent on request size? A library that implements DRBG-AES-CTR will implement AES-PRF, which can be used as a "chunkable" PRF. Nov 21 comment CTR DRBG dependent on request size? I respectfully disagree. A DRBG is not meant to be used as a PRF. It is only meant to generate bits that are to be used where ideally completely random bits should be used. Oct 21 comment SSL implementation in windows? I'm voting to close this question as off-topic because questions about programming, libraries and platform specific APIs may be asked on stackoverflow.com Oct 8 comment How to show something is not a one-way function? @fkraiem: I am saying that the condition "all polynomials $p$" in the definition of strong one-way function your answer, probably isn't what you meant. For all candidate functions, it is possible to choose a constant polynomial that makes the inequality false. Hence, no strong one-way functions exists. Oct 8 comment How to show something is not a one-way function? $p(n) = C$ is a polynomial. Oct 7 comment Are there MD5 collisions for inputs of different length? @ddddavidee: MD5 has an input length constraint of max $2^{64}-1$ bits. You can't have $2^{128}+1$ unique MD5 inputs each with a unique length. Oct 7 comment How to find the value of a vector modulo a basis in lattice-based cryptography Would it help to know that you will find the definition and a formula on page 12 of the paper? Cf: crypto.stanford.edu/craig/craig-thesis.pdf#22 Oct 5 comment Weird base64-like (?) encoding Such encodings can be produced by any large arithmetics library that supports conversion of octet strings to integers and of integers to arbitrary base representation. It is however not on topic here.