Reputation
536
Top tag
Next privilege 1,000 Rep.
See votes, expandable usercard
Badges
4 12
Newest
 Commentator
Impact
~47k people reached

Apr
29
awarded  Commentator
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 $H(K | C) = H(M) + H(K | M, C)$.
Feb
28
awarded  Good Answer
Feb
9
awarded  Enlightened
Feb
9
awarded  Nice Answer
Dec
20
awarded  Excavator
Dec
20
revised Does IKEv2 protocol have two modes like IKE
Just nitpicking: RFC 4301 suggests "IPsec" as the correct capitalization/spelling.
Dec
20
suggested approved edit on Does IKEv2 protocol have two modes like IKE
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.
Jun
22
awarded  Caucus
Oct
17
awarded  Yearling
Apr
2
awarded  Nice Answer
Jan
17
awarded  Announcer
Oct
20
awarded  Scholar
Oct
20
accepted The meaning of “scheme”
Oct
17
asked The meaning of “scheme”
Jul
12
awarded  Yearling
Jul
4
awarded  Editor
Jul
4
comment Setting protocol parameters to achieve concrete security
@PaĆ­loEbermann: Yes, thanks! Corrected.