Mok-Kong Shen

295 reputation

bio	website
	location
	age
visits	member for	9 months
	seen	2 days ago
stats	profile views	10

	295 reputation	bio	website		visits	member for	9 months
6 badges		location			seen	2 days ago

summary answers questions tags badges favorites bounties reputation activity

90 Actions

suggestions reviews revisions comments badges posts accepts all

Feb 5	comment	How to check the strength of an encryption algorithm? @CodesInChaos: Commonly a new algorithm wouldn't likely contain brand-new (invented) primitives but is simply some "presumably" new (advantageous) way of employing (arranging) certain already known types of primitives e.g. S-boxs etc. If one posts such algorithms, could that be on-topic?
Feb 5	comment	Source for examples with broken cryptography NSA had designed an algorithm on which an attack was found only hours after its declassification. See en.wikipedia.org/wiki/Skipjack_%28cipher%29
Feb 5	comment	How to check the strength of an encryption algorithm? I doubt that it conforms to the general guiding principles of this forum that one posts a particular algorithm and asks how to check whether it is secure enough or not. Could someone clarify that issue?
Feb 5	comment	Any implication of a Yale result to security of quantum cryptology? There is a very recent paper arxiv.org/abs/1301.7351 by R. Anderson and R. Brady entitled "Why quantum computing is hard - and quantum cryptography is not provably secure". I should very much appreciate it, if some experts could evaluate that paper.
Feb 4	comment	Entropy in natural language texts I meant that, if a good lower estimate is known, one could, to be conservative, use a somewhat still smaller value and thus be able with a rather simply coding to obtain letter sequences that achieve sufficiently high entropy value for practical use. (The main point is simplicity.)
Feb 4	comment	Generate random number which should depend on key If something can't be simply twisted to work, one has to look for alternatives. I suppose that a sufficiently good scheme that can be adapted for use in your applications could be RC4, see Wiki.
Feb 4	comment	Entropy in natural language texts The book I read does say that was Turing's estimate of "entropy". So I don't understand yet your critique concerning the estimate as such. It could well be though that one should use a revised value nowadays. Simplicity I meant refers mainly to the concept and coding.
Feb 4	comment	Entropy in natural language texts Firstly, it could serve other purposes than "directly" for encryption, for example to generate keys for ciphers. Secondly, if it turns out to be a satisfactory way to obtain entropy-rich sequences, than its usage as key stream for stream encryption would also be practically feasible. Awkwardness you mentioned is a rather subjective issue. What really counts would be simplicity and that is the case with the scheme IMHO.
Feb 4	comment	Entropy in natural language texts For practical applications, one commonly doesn't always necessarily require theoretical unconditional security. No crypto algorithm used in practice is absolutely theoretically secure IMHO. In other words, one does compromises to achieve one's purposes in some presumably optimal way.
Feb 4	asked	Entropy in natural language texts
Feb 3	comment	What are some different cryptography methods? Elliptic curves and chaos theory are among the answers IMHO.
Feb 2	comment	Any efficient text-based steganographic schemes? IMHO it would be better to avoid frequent modifications of the same piece of text in order not to cause suspicions of the warden, i.e. one simply employs instead other viable channels that transmit new pieces of texts.
Feb 2	awarded	Editor
Feb 2	revised	Any efficient text-based steganographic schemes? added 205 characters in body
Feb 2	comment	Any efficient text-based steganographic schemes? I guess that a weak point of translation-based stego is: Why should a sender send a (poor quality) translation and not the original so that the recipient could have it translated himself (there being facilities on the Internet) and also have the original to check in case ambiguities arise? That question might lead the warden to wonder under circumstances IMHO. On the other hand poor quality messages presumably could work well, if the sender is known to be fairly poor in language competence, e.g. an immigrant taking yet a language course.
Feb 2	comment	Any efficient text-based steganographic schemes? But the editing must have some sense at the superficial level and that would be difficult, wouldn't it? Wouldn't very frequent editing attract suspicions of the warden?
Feb 1	comment	Any efficient text-based steganographic schemes? Accidental trailing spaces are by definition rare. If a stego scheme capitlizes on exploiting trailing spaces, there would be lots of them to attract the warden's attention. Of course almost everything in the real world is connected with probabilities. There is barely 100% surety. One knows that even courts sometimes (have to) base their verdicts on the so-called presumptive evidences and thus occassionally innocent people go to jail because of that.
Feb 1	comment	How to best obtain bit sequences from throwing normal dice? I have computed the values of efficiencies for different number of rolls in increasing order (in parentheses is value of the method described by Thomas) up to 100 rolls: 1 1.66667 (1.33333), 2 2.33333 (2.22222), 4 2.38272, 7 2.53178 (2.40800), 12 2.57454 (2.54856), 24 2.57598, 36 2.57708, 48 2.57712, 53 2.58454 (2.57951)
Jan 31	awarded	Supporter
Jan 31	comment	How to best obtain bit sequences from throwing normal dice? The method you described for both single and two rolls are very fine for the practice, I believe. One just have to look up in a table to write down the bits. For three rolls, however, there is a drop in efficiency, if my computation is not in error. (For the method described by Thomas the efficiency of using 3 rolls is also less than that of using 2 rolls.)