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visits member for 2 years, 11 months
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I'm an engineer with experience in applied cryptography, in particular in Smart Card systems.


5h
comment Secure way to store fixed size string of digits
Define "securely". $\;$ You want to achieve confidentiality, but what about integrity, and high insurance of availability despite hardware mishaps? $\;$ When you need the data, is it for the purpose of testing if some string is that 9-digit string, or do you need to retrieve that value? $\;$ If you can retrieve that 9-digit string value, and the adversary can't, what can the system use to differentiate you from the adversary? $\;$ What is it reasonable to believe an attacker can/can't do on your system?
7h
comment RSA with modulus n=p²q
@bmm6o: Ah right, I had missed that.
7h
comment Which algorithm do you recommend for practical use to generate unique passwords for each website?
Many sites have password requirements than make the "Turn the site secret into a usable password" step non-trivial, and hard to get right; like (I'm not making that up): At least 15 characters. Contains CAPITAL Letters. Contains SMALL letters. Contains either special characters or numbers (e.g. / , *, @, #, $, or 1, 2, 3 etc.). $\;$ Typically that spec is imprecise, often hard to get or/and existing in different versions, and more often than not wrong (e.g. here, the system actually allows both special characters and numbers, and I'm not even sure that it does not require that).
9h
comment RSA with modulus n=p²q
The potential saving is actually greater than for multiprime RSA with 3 primes, because there are only 2 expensive modexp to perform, rather than 3. On the other hand, the modified CRT is quite a bit unusual.$\;$ Note: To get the paper, a click on "download chapter" on the page you link works for me; and then I can save the PDF (I believe, legally); that's a fortunate consequence of the IACR copyright policy.
10h
comment RSA with modulus n=p²q
@Ricky Demer: I fail to see why the restriction to coprime $j$ and $k$. $\;$ That $\gcd$ trick is nice!
10h
comment RSA with modulus n=p²q
@Ricky Demer: FYI, with Firefox on Win7, your technique to force line breaks in comments using computed space works, or not, depending on the zoom (control-mouse-wheel) that I use. $\;$ Follup-up, if any, in this related meta. $\;$ I'll remove this comment after you had time to read it.
14h
revised RSA with modulus n=p²q
Slightly restructure; give standard e.
17h
revised RSA with modulus n=p²q
Fix a formula which was suboptimal (though only when the RNG is hopelessly broken)
17h
comment Reordering non-block-aligned parts with DES in ECB mode
A rainbow table to crack DES encryption, really? If you maintain that assertion, give us details!! Absent these, I consider this is a serious confusion.
1d
revised RSA with modulus n=p²q
More direct link to Fast Variants of RSA
1d
comment MAC using a modified CBC mode of operation
@mikeaso: thanks for the much needed correction!
1d
answered RSA with modulus n=p²q
1d
comment Is my implementation of a PRG at least intuitively secure?
We can tell you the exact opposite: there is not (and can't be) a test, using a PRG as a black box, that can give a useful indication that a PRG is secure; much less a proof. The best a test does is tell that a PRG is not secure. Existing tests of CSPRNGs are designed to catch faulty implementations, or badly misguided (more often than not, both).
1d
answered MAC using a modified CBC mode of operation
1d
comment Is my implementation of a PRG at least intuitively secure?
Without a meticulously precise description of a PRG, one can't conclude that it is secure. Such description is not given, thus the question can't be answered; and it would probably be off-topic anyway. $\;$ Keep in mind that any experimental randomness test not tailored to the PRG tested can only invalidate the hypothesis that it is secure, NOT validate that hypothesis. An analogy: that's similar to a Fermat primality test, which can often invalidate that an integer is prime, but can never tell 1436697831295441 is not prime.
1d
comment MAC using a modified CBC mode of operation
Hint: what happens to the tag when two blocks of plaintext are exchanged?
2d
revised How do we operate IV+1?
Add LFSR variant
2d
revised How do we operate IV+1?
restrict to big-endian
2d
answered How do we operate IV+1?
2d
comment understanding the proof of knowledge
Anything in particular remains unclear after reading Wikipedia's entry on proof of knowledge? Or/and Mihir Bellare and Oded Goldreich's reference article: On Defining Proofs of Knowledge?