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Nov
23
comment Security of simple xor and s-box cipher?
@Polynomial - Consider the case in which you only have one message block, $C_n = S[K_0 \oplus M_0]$. $S$ is invertible and so we are back to the known plaintext attack. You need the second xor of the key to prevent an attacker from inverting S ($C_n = S[K_0 \oplus M_0] \oplus K_0$) . The approach you should take is, to build a secure block cipher that only processes one message block. If it isn't secure with only one block it is unlikely to be secure with more than one block.
Nov
23
revised Security of simple xor and s-box cipher?
This answer no longer applies to the question since the scheme proposed in the question has be drastically changed.
Nov
23
comment Security of simple xor and s-box cipher?
The above scheme does not use multiple rounds but rather uses only one round with a different round key per message block. A multiple round scheme would have the same the same message block be enciphered by more than one round key. You may have conflated CBC with rounds. I think you should probably abandon the CBC stuff until you have a secure block cipher and then figure out how to use that secure block cipher in a CBC mode.
Nov
23
answered Security of simple xor and s-box cipher?
Nov
22
comment Could one construct a cipher that is secure for friendly parties to use but insecure for hostile parties?
@user11342 Where did your answer get moved? I can't seem to find it.
Nov
2
comment How to deduce enigma settings given a partial plaintext?
Yeah, my bad, I redid my calculations and ended up with the same answer as you.
Oct
28
comment How to deduce enigma settings given a partial plaintext?
Nice try, time traveling Alan Turing.
Oct
12
comment Why has the RSA factoring challenge been withdrawn?
Thanks Thomas! Someone should turn this into a question.
Oct
12
comment Why has the RSA factoring challenge been withdrawn?
According the wikipedia page: "[TWIRL'S designers] estimate that if TWIRL were built, it would be able to factor 1024-bit numbers in one year at the cost of 'a few dozen million US dollars'". Is this statement incorrect? Has something new been learned?
Oct
12
comment Why has the RSA factoring challenge been withdrawn?
What about research on custom cryptanalysis hardware such as TWIRL en.wikipedia.org/wiki/TWIRL
Sep
30
comment What is the “Random Oracle Model” and why is it controversial?
+1 for "There is a black box. In the box lives a gnome, with a big book and some dice."
Sep
29
revised Is there a secure cryptosystem that can be performed mentally?
added link to attacks on the Pontifex cipher
Sep
29
suggested approved edit on Is there a secure cryptosystem that can be performed mentally?
Sep
28
comment Is there a secure cryptosystem that can be performed mentally?
OTP's can be done mentally, would you consider OTPs a fair answer?
Sep
28
revised How does HOTP keep in sync?
tex notation, links to wikipedia
Sep
28
suggested approved edit on How does HOTP keep in sync?
Sep
28
revised How to attack a classical cipher using known partial plaintext?
reworded, formatting, links
Sep
28
suggested approved edit on How to attack a classical cipher using known partial plaintext?
Sep
28
revised How can we reason about the cryptographic capabilities of code-breaking agencies like the NSA or GCHQ?
links to wikipedia
Sep
28
revised How to enhance randomness of AES?
changed notation to tex notation