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Nov
2
comment Developing algorithm for detecting plain text via frequency analysis
This is essentially what the OP did before, using $n$-gram frequencies. Alas, if one is only looking at every $k$-th letter in the text, for $k \ge 2$, such pairwise correlations are not very useful.
Nov
2
comment Many time pad attack
@AutonomousApps: Look at the "bin" column in the table you linked. Note that bits are conventionally numbered from right to left, with bit 0 being the rightmost (i.e. the numerically least significant) bit.
Nov
1
comment How is bitslicing faster?
@fgrieu: Honestly, I've no idea. It's been a while since I've done any actual assembly coding myself. I just suggested those as vaguely plausible examples of oddball instructions that could be useful.
Oct
29
comment How is bitslicing faster?
@Thomas: If Galois fields are on topic, I'd say bitslicing is, too. Sure, you could ask this on SO, or perhaps dsp.SE, too, but the answers you'd get there would likely have a different emphasis than what you'd get here on crypto.SE. IMO, like the Galois fields question, this one falls into the legitimate area of overlap between different sites. There have been quite a few papers published in crypto journals about bitslicing; I think that's enough to make it on topic here too.
Oct
28
comment How is bitslicing faster?
Anyway, if all you'd like is some more descriptions of the technique, perhaps the original paper on DES bitslicing (Biham, 1997) or this paper on AES bitslicing (Käsper & Schwabe, 2009) may be useful.
Oct
28
comment How is bitslicing faster?
I'm sorry if I'm being unreasonably suspicious, but what you've written above sounds just a little bit uncomfortably like a "please answer my homework assignment for me" question. If this is not, in fact, the case, it might help if you could provide a bit more context for your question, and perhaps specify what exactly about bitslicing you're having trouble understanding.
Oct
27
comment How is digital signature different from a message authentication code (MAC)?
+1; also, the deniability of MACs may sometimes be considered a desirable property, e.g. for encrypted private communications where you may not wish to leave the other party with a permanent proof of what you said to them.
Oct
27
comment How is digital signature different from a message authentication code (MAC)?
...and then there's also What are the differences between a digital signature, a MAC and a hash?
Oct
27
comment How is digital signature different from a message authentication code (MAC)?
@archie: It is indeed a dupe, although I really think that this one is the better question of the two. On the other hand, poncho's answer over there is good, so... dunno. Maybe we could close that question as a dupe of this one, and have a mod merge the answers?
Oct
26
comment Can a monoalphabetic substitution cipher attain perfect secrecy?
(In any case, honestly, if you understand what "monoalphabetic substitution cipher" and "perfect secrecy" mean, what I posted above should essentially answer the question. All I really left out was the single word "yes/no" -- you'll have to spend a few seconds thinking for yourself to see whether my answer is a proof or a disproof of perfect secrecy.)
Oct
26
comment Can a monoalphabetic substitution cipher attain perfect secrecy?
@arsaKasra: There's no law against it, but many consider it poor form to spoon-feed complete answers to people asking homework questions. After all, the purpose of homework is to teach you how to figure out answers to such questions yourself. Now, if you honestly have the same problem, and need the answer for some purpose other than homework (although, for this particular question, I can't really imagine what it could be), let me know, and I'll be glad to amend my answer.
Oct
23
comment Is it possible to combine cryptography with steganography
Alternative "solution": Generate a bunch of watermarked versions Ms of the message M, encrypt each of them with the corresponding recipient's key (you can use standard symmetric or public-key crypto here) and combine all the encrypted messages into Me. Each recipient just extracts the piece of Me that is encrypted with their key, and decrypts it. Obviously, this produces a very long Me if there are lots of recipients, but otherwise it seems to meet your requirements.
Oct
23
comment Is it possible to combine cryptography with steganography
If each key only needs to be able to decrypt one message, why not put the watermarked message for each recipient in their "key", and just use a dummy "message"? (OK, one possible reason is if you need to be able to generate the keys before you know the message.)
Oct
23
comment Is it possible to combine cryptography with steganography
I assume there's an unstated requirement that Alice should be able to send the same encrypted message to multiple recipients, each having their own decryption key, and have them each obtain a distinct watermarked copy when they decrypt it? And presumably also that each decryption ḱey can be safely used to decrypt arbitrarily many messages, without allowing the watermark to be removed? Is it also possible for the recipients to collude to defeat the watermark? (In reality, it generally is, but it tends to make designing reliable watermarks much harder.)
Oct
22
comment Is there an existing cryptography algorithm / method that both encrypts AND compresses text?
@supercat: The closest thing I can think of, off the top of my head, is the use of straddling checkerboards in some WWII-era and later Soviet ciphers. But those ciphers had numerical ciphertext anyway, so they weren't particularly quick to transmit by Morse anyway.
Oct
21
comment Is there an existing cryptography algorithm / method that both encrypts AND compresses text?
@RickyDemer: You don't even need digital signatures for that. Just take any secure block cipher with a $k$-bit block size, and a (privacy-preserving) $k$-bit MAC, and define your encryption function to apply the block cipher if the input is exactly $k$ bits long, and the MAC otherwise. Then applying the inverse block cipher will, given any output, always yield a matching input.
Oct
5
comment Generating unbiased numbers with a biased six sided die?
I'm voting to close this question because it's about general mathematics without any specific cryptographic elements. Such questions are off-topic here, but may be asked on Mathematics. (Mind you, they don't tend to like "do my homework for me" questions there, either.)
Oct
3
comment Is it possible to create “non overlapping” RNGs?
+1. Also, if you need the outputs to lie in a range that doesn't conveniently match the block size of any standard block cipher, you can use the usual FPE tricks to construct a cipher with a suitable range.
Sep
26
comment Signing and verifying message consisting of several parts
@Mr.Vendetta: To verify message part $m_i$, given the master hash $h$, you first load the hash list $(h_0, h_1, \dots, h_n)$, check that $H(h_0 \| h_1 \| \dots \| h_n) = h$, and then check that $H(m_i) = h_i$. That's a lot faster than loading and hashing the entire message $m = (m_0, m_1, \dots, m_n)$.
Sep
23
comment How can AES + cycle walking be used as an FPE?
@erotavlas: No, not if you want to keep the system format-preserving.