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


7h
comment Use case of RSA CRT
More reasons, especially in Smart Cards: $\;$ a) It is slightly involved to derive the CRT key $(p,q,dp,dp,qInv)$ from $(n,d)$, which may be the specified form for key injection. $\;$ b) If all we know is that the key is per PKCS#1 and $N$ is $k$-bit, $p$ might still be much more than $k/2$ bits, so perhaps for some keys it does not fit the available hardware well and CRT gives no time savings. $\;$ c) As mentioned in answer, the CRT form of the key requires more space, about +75% more since $(N,e)$ needs to be available in order to check the result as a countermeasure against fault attacks.
13h
comment Crypto (mainly binary
This is squarely off-topic. And there is not enough data, and most importantly context, to determine what this encoding is.
18h
revised Small Prime Difference in RSA
Undo fix of Fermat's runtime
1d
revised DES-X , computation load and storage
added 2 characters in body
1d
comment Operation which needs much computing power to be created, but just a little to be solved?
@stereo_: What's "a crypto CTF" in your comment about the use case? $\;$ Does a Proof-of-Work system combined to adding the plaintext in clear to the problem fits your needs? If not, why? Note: answer that my clarifying your question (hopefully, you can use the edit button).
1d
accepted Is AES's parity key-dependent?
1d
asked Is AES's parity key-dependent?
1d
comment A simulation for the BB84 quantum key distribution protocol
Duplicate of Quantum key distribution simulation
1d
revised Small Prime Difference in RSA
Remove extra negation
1d
revised Small Prime Difference in RSA
Revise comment (and turn quotient upside down) on Fermat's computing cost
1d
revised Small Prime Difference in RSA
Change the theorem, so that its proof does not require a boring thechnicallity
1d
revised Small Prime Difference in RSA
Change the theorem, so that its proof does not require a boring thechnicallity
2d
awarded  Nice Answer
2d
revised Small Prime Difference in RSA
Beautify
2d
revised Small Prime Difference in RSA
deleted 32 characters in body
2d
revised Small Prime Difference in RSA
Polish last step of proof.
2d
revised Small Prime Difference in RSA
Expand and reformat
2d
revised Small Prime Difference in RSA
got a simple algorithm
2d
comment Small Prime Difference in RSA
@mikeaso: Your technique makes $(p-q)/2$ guesses. $\;$ I initially thought it was equivalent to the Fermat factorization method (see Wikipedia or MathWorld), but the later makes about $(p-q)^2\over8\sqrt n$ guesses, which can be MUCH less. With $n=2189284635403183$ (such that $p-q=18)$, your technique makes $9$ guesses, Fermat's only $1$. With the similarly sized $n=2189283205227561$ (such that $p-q=40040)$, your technique makes $20020$ guesses, Fermat's only $5$.
2d
answered Small Prime Difference in RSA