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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.
May
16
comment True random numbers generated by sensors
Many people seem to think we should "not harvest the bits generated when it's not moving", or "only use the bottom 8 bits from some samples", or "xor together" data from various sources and only put the single final result into the entropy pool. However, the top answer from "use all and hash, or trim least significant bits?" recommends feeding all directly directly into the CSPRNG, and let the CSPRNG handle any "hashing" or "XORing" that needs to be done.
May
5
comment Theoretical pi-based stream cipher
Good point. Some numbers do have more "1"s than "9"s in its decimal representation, even if that number is normal. But I was under the impression that most mathemeticians believe that not only is pi normal, but also that the decimal representation of pi has (as far as we know) exactly the same number of "1"s, "2"s, "9"s, etc. -- see "Frequency of Each Digit of Pi" by Eve Andersson. What evidence is there that the distribution is distinguishable from random?
Apr
25
comment Theoretical pi-based stream cipher
@Thomas: "most certainly"? Many mathematicians would be very surprised if it turns out that pi is not a "normal number". Are you really saying "I have discovered a truly remarkable proof of this theorem which this margin is too small to contain."?
Feb
23
comment Algorithm/Technique for Steganography
Some of the steganography schemes listed at crypto.stackexchange.com/questions/6058/… are more efficient, in the sense of requiring a smaller file to send the same number of ciphertext bits.
Feb
1
comment Any efficient text-based steganographic schemes?
@Mok-KongShen: Yes, the warden can easily detect trailing whitespace -- but often trailing whitespace accidentally and innocently ends up in files I write and others as well. How can a warden detect a real covert channel without getting false positives from such innocent accidental whitespace? If the warden cannot distinguish innocent random whitespace from a real covert channel, then the steganographic channel is secure IMHO.
Dec
9
comment Public key cryptography - public key encrypts and cannot decrypt?
+1 nice explanation. ArtOfTheProblem uses a similar but possibly easier-to-understand explanation in their "Public Key Cryptography: RSA Encryption Algorithm" youtube video.
Dec
1
comment Software implementation of a commutative cipher?
Number of intersections of two sets gives some interesting algorithms that apparently can tell you if you have any SSNs in common, and if so, how many, without leaking any more information.
Nov
13
comment Stretching passwords for encrypting small files
+1 for linking to a complete interoperable best-practice standard for encrypting files -- OpenPGP -- rather than mentioning one particular primitive or another, which all too often are used incorrectly or at least in unnecessarily incompatible ways.
Nov
2
comment Is there a symmetric-key cryptography based on key establishment techniques?
@D.W. : Yes, Wikipedia's Kerberos protocol article lists a few RFCs that explain the protocol. I wish someone would edit Simple Wikipedia's Kerberos protocol article to explain it in a way that normal humans could understand.