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Mar
17
comment Randomness test question from FIPS 140-1 and comparison with 140-2
As for the probability of failure with a good source, the monobit test is set for 5 standard deviations (FIPS 140-1) and 4 standard deviations (140-2). This implied a false failure probability from this test alone of 1 in 800,000 (140-1) or 1 in 8,000 (140-2)
Mar
17
comment Randomness test question from FIPS 140-1 and comparison with 140-2
The other thing to note is that with FIPS 140-2, there's only a handful of approved RNGs (RBGs); the ones listed in NIST SP 800-90, the X9.31 generator, one from 186-2 and the X9.62 generator. All these use cryptographical primitives, and may fail (that is, not provide sufficient unpredictability) if given insufficient entropy, but a statistical test will not catch that. Hence, there's nothing that these statistical tests bring to the table (plus these tests have a nontrivial probability of failing on a good stream)
Mar
16
comment Elliptic Curves of different forms
Actually, I believe P-256 cannot be made into a "safe curve" (at least, not without help from whoever selected the curve) because one of the requirements is "rigidity", that there are no unexplained constants involved, and P-256 (and the other NIST curves) have the constant $b$ that has not been explained.
Mar
15
answered Verifying multiplicative inverse on a prime field in NIST's ECDSA_Prime.pdf
Mar
15
answered RSA problem if i choose two specific small prime numbers?
Mar
15
awarded  Enlightened
Mar
15
awarded  Nice Answer
Mar
14
comment Is this an acceptable implementation of ARC4 encryption for my system?
@traxonja: alternatively, you can generate tags using CMAC (RFC4493); that's pretty much CBC-MAC with a few tweaks to avoid weaknesses arising from variable length messages.
Mar
14
comment Is this an acceptable implementation of ARC4 encryption for my system?
@traxonja: no, CBC-MAC provides integrity but not encryption. It's actually fairly simple, you act as if you are generating the CBC mode encryption of the message, but is discard everything except the last ciphertext; that's your tag (and you can use, say, 72 bits out of that as your tag). Now, both sides do this 'CBC mode encryption' in the encrypt direction (because both are generating tags -- the receiver compares what he generates with the tag in the message).
Mar
13
revised How does the key size per data bit influence the security?
English nit
Mar
13
answered How does the key size per data bit influence the security?
Mar
12
comment How to best mix two arbitrary/random n-bit words?
@Mok-KongShen: well, natural language texts are quite compressible, it should be quite possible to compress both texts into half their size. Once you've done that, concatinate the two compressed halves together; this result has all the entropy of the original texts, and hence is an optimal solution (to the very specific problem you stated).
Mar
12
comment Mapping of message onto elliptic curve and reverse it
Also, instead of attempting to use ElGammal, you could use the Elliptic Curve Integrated Encryption System, that works better, and the problem you have just doesn't come up
Mar
12
comment Is this a pseudo random function (PRF)? F(k,x) = f(k,x) - f(k,x-1)
@tylo: I believe that the proof can be summarized as "if you are limited to no more than $2^n-1$ queries, then if $f(x)$ is a random function, then $f(x)-f(x-1)$ is a random function", and then "if $f(x)-f(x-1)$ can be distinguished from a random function, then $f(x)$ is distinguished from a random function"
Mar
12
comment Is this an acceptable implementation of ARC4 encryption for my system?
You could use either AES-CMAC, or since your messages are fixed length, plain-old CBC-MAC would work. As for whether 9 bytes would be enough, that would mean that if someone without the key sent you forged messages, then they would need to send 4 trillion messages before they have 1 in a billion chance that one would get through; is that sufficient?
Mar
11
comment How to best mix two arbitrary/random n-bit words?
@Mok-KongShen: define "optimally".
Mar
11
reviewed Edit suggested edit on How to best mix two arbitrary/random n-bit words?
Mar
11
revised How to best mix two arbitrary/random n-bit words?
Missed a few last time.
Mar
11
revised How to best mix two arbitrary/random n-bit words?
added 5 characters in body
Mar
11
reviewed Approve suggested edit on How to best mix two arbitrary/random n-bit words?