Reputation
3,744
Top tag
Next privilege 4,000 Rep.
Access 'trusted user' tools
Badges
3 17
Newest
 Revival
Impact
~44k people reached

May
5
answered Encrypt file name
May
4
comment Alice and Bob's crush
Sociallist's millionaire problem is wrong in this case, because it answers the function $x=y$. If both input no, they shouldn't be informed that their input was equal. Even worse: This reveals both inputs to both parties: They know their own input, and they learn if their input was equal. So in either case, the other input can be derived.
May
4
comment How to decrypt unusual Many Time Pad
Both $C_0$ and $C_1$ serve no purpose at all. In order to decrypt and retrieve $P_0$, all you need is $R_1$. So if we assume the key contains $R_1$, I can decrypt even if I only get $C_2$ and not $C_1,C_2$. Sending random things alongside actual information does not mean it is any different than the original scheme.
May
4
comment Is there a format preserving cryptographically secure hash?
As noted in the last sentence, it should be a cryptographically secure one. I am not entirely sure if it is strictly needed, but it wouldn't hurt.
May
4
revised Are well designed crypographic codes unbreakable? (NOT ciphers)
added 1328 characters in body
May
4
comment Why are there no OTP ciphers?
@cpast That's why I said "almost". In very specific circumstances, it can be useful. For example if you have the possibility to exchange arbitrary amounts of data now safely, and want to exchanges messages later. However, key management and secure storage are still major issues, and many of the "oh let's use OTP" ideas disregard this entirely.
May
4
comment Integer encryption preserving equality
Probably I would just use AES in OFB mode. When encrypting and decrypting, just pad it with zeros and throw away that part of the result afterwards.
May
4
comment Zero knowledge / proof of knowledge sudoku solution
One of the important details is: What can Bob actually observe? If Alice can swap out cards before or during the shuffling, that would destroy the proof.
Apr
30
comment Why aren't zero-knowledge proofs used for authentication in practice?
Authentication via ZKP is much saver than password login, however it is much less usable. Especially if you use different computers, things get tricky, because then you have to transfer the secret from one machine to the other somehow.
Apr
30
comment Are well designed crypographic codes unbreakable? (NOT ciphers)
And therefore, the argument still stands: If you consider ciphertext only and very few samples, codes are fine. But that is a fundamentally wrong definition of security in today's world, where we AT LEAST need security against known plaintext attacks.
Apr
30
comment Are well designed crypographic codes unbreakable? (NOT ciphers)
Unfortunately, you make the wrong conclusions there. While it is true, that for old languages there are problems translating them, this has no relevance to anything we want to actually use. The fact that we know very little about a language makes its usage impossible. No one can use that language. And there is a fundamental difference between codes and ciphers: Security. It is nonexistent in codes. They do not posses that property on their own. They rely only on the fact that the codebook is unknown, and nothing else. Using any code often automatically makes it unsafe to use.
Apr
30
comment Why are there no OTP ciphers?
"we all love the OTP" Wrong. No one does, becaus 99% of the time people don't get that OTP is only of theoretical interest. It has (almost) no practical applications. It's like saying "Stop killing animals for their meat! If you want meat, buy it from the supermarket." OTP shifts the problem from encryption to key management. That's it.
Apr
30
answered Are well designed crypographic codes unbreakable? (NOT ciphers)
Apr
29
answered Integer encryption preserving equality
Apr
29
revised Zero knowledge / proof of knowledge sudoku solution
added 381 characters in body
Apr
29
answered Zero knowledge / proof of knowledge sudoku solution
Apr
28
comment Permuted vectors
On a sidenote: It would be equally secure if there was just one permutation applied to both vectors, because you tell the malicious server anyway which positions in the vectors correspond to each other.
Apr
28
comment Bilinear map + commitment
Well yes, but how does that help anything. A central question, which is still not clear: Who commits to what, and what are the commitment properties? Binding and hiding properties are what matters for commitments, and you don't mention the revealing either: Who should be convinced, that A and B commited to their messages prior to the unveiling phase?
Apr
28
answered How to attack the Two Time Pad?
Apr
28
answered Is a padding oracle attack possible if data is only encrypted internally on a server (e.g. for storage)?