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I'm an engineer with experience in applied cryptography, in particular in Smart Card systems.


1d
comment Is it possible (how difficult) to find MORE than one valid RSA signature?
The answer depends on if A) signatures verifiable by different public keys count; B) the scheme is deterministic [e.g. ISO/IEC 9796-2 methods 1 and 3] or not; C) access to the private key function $x\to x^d\bmod N$ is available; D) details in the verifier definition/implementation, e.g. is $S+N$ just as valid as $S$.
2d
comment What is the length of an RSA signature?
In some RSA variants, including ISO/IEC 9796-2 (with total message recovery, and the "Signature production function" rather than the more common "Alternative signature production function"), the signature is a bit string of $\lceil\log_2N\rceil-1$ bits, corresponding to (the big-endian encoding of) an integer between $1$ and $(N−3)/2$: that is $\min\big(J^s\bmod N,N-(J^s\bmod N)\big)$ where $J$ is a function of the message to sign and parameters.
Sep
16
comment How to calculate kinv from the given k value
Closely related to this question
Sep
16
comment Is Rabin's cryptosystem secure against known-plaintext attacks?
Is your Rabin's cryptosystem different from Rabin public-key encryption in the HAC, section 8.3? If yes, how?
Sep
12
comment Self-Convergent Hashing
What about giving a better description of that algorithm class, so that it would be recognizable? $\;$ In particular, are you meaning the algorithm hashes something including its own result, or something including its own definition in some grammar?
Sep
12
comment How can one generate pairs/triplets/…/n-ary MD5 collisions
A relevant paper (to the second part of the answer) is Joux: Multicollisions in Iterated Hash Functions. Application to Cascaded Constructions‌​, in proceedings of CRYPTO 2004. $\;$ That's related to length extension attack, but not exactly it; rather, an extension.
Sep
11
awarded  Nice Answer
Sep
11
awarded  Nice Answer
Sep
8
revised What are options to compute DES retail MAC (aka ISO 9797-1 mode 3) under PKCS#11?
Fix the name of the approriate mechanism
Sep
6
accepted What are options to compute DES retail MAC (aka ISO 9797-1 mode 3) under PKCS#11?
Sep
6
answered What are options to compute DES retail MAC (aka ISO 9797-1 mode 3) under PKCS#11?
Sep
6
comment What are options to compute DES retail MAC (aka ISO 9797-1 mode 3) under PKCS#11?
@poncho: Ah, I had misunderstood your comment. I'll fix that with an answer.
Sep
6
revised Why does FIPS 186-4 require specific sizes for keys?
Add link and tag
Sep
5
comment Base64 for a hash algorithm
It is very common to post-process a hash's result using base64, and the resulting algorithm could be considered a hash. If so, that resulting algorithm is a hash algorithm that uses Base64 in (the final phase of) the process of hashing a string. $\;$ That question has no clear-cut answer as stated.
Sep
5
revised Is it possible to generate a secure permutation F over 32-bit integers even if F(0) … F(n) is public knowledge?
Incorporate comments
Sep
5
revised Is it possible to generate a secure permutation F over 32-bit integers even if F(0) … F(n) is public knowledge?
retag
Sep
5
answered Is it possible to generate a secure permutation F over 32-bit integers even if F(0) … F(n) is public knowledge?
Sep
4
revised What are options to compute DES retail MAC (aka ISO 9797-1 mode 3) under PKCS#11?
mention the requirement of using DES in the token only
Sep
3
asked What are options to compute DES retail MAC (aka ISO 9797-1 mode 3) under PKCS#11?
Aug
29
comment Are there other digital certificate formats than X.509?
The title of that quote is not even wrong, as a type can't be meaningfully compared to a certificate. $\;$ And truth is: NOT all Digital Certificates are also a X.509 certificate.