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Jan
24
comment Impact of distinguishing between random text and cipher text?
Wikipedia: Feistel cipher currently claims that '4 rounds are sufficient to make it a "strong" pseudorandom permutation'. Is Wikipedia wrong, or am I misunderstanding Patarin or Wikipedia or both?
Jan
13
comment Convert old and busted password encryption to something sensible
related: Increase the security of an already stored password hash
Jan
12
comment Is there a simple hash function that one can compute without a computer?
related: crypto.stackexchange.com/questions/11691/…
Jan
2
comment How does the secret key in an HMAC prevent modification of the HMAC?
@StephenTouset, by "appending data to the end", I think George is referring to a length extension attack, which is not trivial.
Dec
29
comment Salts, how does the script know what the salt is?
Yes, and often the name of the hash algorithm is also concatenated to the salt and the hash, in Modular Crypt Format or LDAP / RFC2307 format.
Nov
13
comment How can we get CA's public key?
@CodesInChaos: make that an answer.
Nov
12
comment How would I make a secret notation alphabet more secure?
You might enjoy looking at shorthand systems such as Gregg shorthand -- they were never intended to be difficult to decode, but some stenographers use so many of their own custom abbreviations that even other stenographers using the same system have difficulty reading it.
Nov
12
comment Is this hand cipher any more secure than the Vigenère cipher?
You could get a lot better diffusion if, rather than handle each letter independently with "mod 26", you allow a carry over -- i.e., when adding 5 to X and obtaining C, you get a "carry over" that changes the next column from E+3=H to E+3+1=I.
Oct
23
comment What is the most secure hand cipher?
@makerofthings7: if it is used properly, as Smit Johnth pointed out, then OTP is completely immune to statistical analysis and every other kind of ciphertext-only analysis, no matter how the letters are encoded into numbers -- ASCII, Baudot code, Morse code, etc. See Wikibooks: one time pads for more details.
Oct
16
comment Any efficient text-based steganographic schemes?
This steganographic scheme is called an acrostic ( Wikipedia: acrostic ).
Aug
4
comment Why are there $ signs in my passwd file?
+1. Recently people at Wikipedia shuffled things around. Is crypt (C) on Wikipedia what this answer ought to link to?
Jul
16
comment Physical analogue for MACs
+1. To make this more analogous to a real MAC, we could assume that an attacker could steal the case (and everything inside it) and substitute a similar-looking one of his one -- only someone with the "real" key would discover that it doesn't unlock the replacement case, just as only someone with the real secret key can tell that a substituted message with a substituted MAC isn't the original message.
Jul
15
comment Physical analogue for MACs
@Reid -- you have two pretty good ideas here; I wish you had posted them as two separate answers, so that the "better one" (whichever that may be) would float to the top. +1 anyway.
Jul
13
comment Physical analogue for MACs
@PaĆ­loEbermann: Yes, that's how most MACs work -- everyone who can check the MAC can also produce their own. When teaching people about MACs, we want the physical analogue to have the same flaws as the actual MAC.
Jun
6
comment How can I split a message in parts of similar size or smaller?
Yes, your scheme is a pretty clever way to reduce the size.
Jun
6
comment How can I split a message in parts of similar size or smaller?
+1 for a working 3-of-3 approach. I'm pretty sure tha 2-of-3 (or X-of-Y) threshold schemes require longer messages; one approach is the very similar ssss and SecretSplitter.
Jun
4
comment Encrypt-then-MAC paradigm
The answers to Should we MAC-then-encrypt or encrypt-then-MAC? discuss the security properties of Encypt-then-MAC and compare them to MAC-then-encrypt and MAC-and-encrypt.
Jun
3
comment Encrypt user email but be able to find user by email
+1 Looks good. For some applications, if the attacker already has an email address on his list, then he can already send spam to that address -- it doesn't hurt anyone if that attacker can confirm that you have the same address on your list (or not). So for those applications, non-keyed hash functions are adequate. See suppression list and Store hashed email and compare hash values.
May
25
comment How random are commercial TRNGS
By "radio", are you perhaps referring to hardware random number generators based on radioactive decay, such as hotbits ?
May
16
comment Are picture files “random enough” to be usable as a one-time pad?
@PaĆ­loEbermann: Yes, Lavarand shows that, with (a) photographs that have adequate randomness, and (b) a good randomness extractor, one can produce excellent truly random numbers.