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Apr
29
comment Perfectly secret cipher can leak about the key?
Cont'd: The extra term (w.r.t what Habib wrote) vanishes only if $K$ is uniquely determined from $M$ and $C$, which is the case with one-time pad. However, $H(K|M,C) = 0$ does NOT hold for all perfectly secure ciphers. For instance, assume the message & ciphertext spaces are $\{00,11\}$, the key space is $\{00,01,10,11\}$. It's easy to define a perfectly secure cipher over these spaces. Since the key space is larger than either of the message and ciphertext spaces, the key will not be uniquely determined from $M$ and $C$.
Apr
29
comment Perfectly secret cipher can leak about the key?
@Incredible: What you said is correct regarding a general deterministic cipher with independence of $M$ and $K$. Habib is talking about a perfectly secure cipher. In section 7.3 of the book Codes and Ciphers, an even more general identity is proven (it assumes neither determinism nor independence of $M$ and $K$): $H(K | C) = H(M | C) + H(K | M, C)$. In case of a perfectly secure cipher, $H(M | C) = H(M)$, and it can be written as $H(K | C) = H(M) + H(K | M, C)$.
Dec
18
comment How can I implement the elliptic curve MOV attack myself?
I also suggest taking a look at this question and its answer. Samuel Neves uses Sage to implement the attack, the code being posted here. I think you can get some ideas for your own implementation just by looking at this Q&A.
Jul
4
comment Setting protocol parameters to achieve concrete security
@PaĆ­loEbermann: Yes, thanks! Corrected.
Jun
30
comment Setting protocol parameters to achieve concrete security
Cross post: cstheory.stackexchange.com/q/11816/873
Apr
23
comment What tests can I do to ensure my PRNG is working correctly?
NIST has its own test suite, called "Statistical Test Suite" (STS). It is downloadable from csrc.nist.gov/groups/ST/toolkit/rng/documentation_software.html.
Oct
21
comment Why doesn't preimage resistance imply the second preimage resistance?
Look at this paper: Cryptographic Hash-Function Basics: Definitions, Implications, and Separations for Preimage Resistance, Second-Preimage Resistance, and Collision Resistance.
Aug
24
comment Is it safe to encrypt a public key alongside a message with AES?
@PaĆ­lo, shino: Thanks a lot for the appreciation. I thought it was too short to be made an answer, thus I left it as comment. Moreover, Marsh Ray's answer complements mine, and is long enough ;)
Aug
24
comment Is it safe to encrypt a public key alongside a message with AES?
AES is secure against known-plaintext attacks, though I suggest not using ECB mode in the case you're going to encrypt M+P. Using CBC or CTR modes seem to be OK.