Mok-Kong Shen

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Mar 26	comment	Any efficient text-based steganographic schemes? A grille is commonly classified as a transposition cipher if I don't err.
Mar 23	comment	Export from US of crypto software with key-size > 56 bits still needs permission? Right. I simply want to caution too optimistic interpretations of that document without serious and careful examinations. (An analogy: certain commercial contracts commonly contain in footnotes and in difficult to read tiny fonts some "non-trivial" passages.)
Mar 23	comment	Export from US of crypto software with key-size > 56 bits still needs permission? Maybe I am thinking in a gravely wrong pedantic direction. But a software/technology which "has been" made available without restrictions ... is not identical to the same stuff that up to the present has not been made available ... but is now going to be made available ... for the first time, isn't it? If yes, that passage wouldn't as such exempt control and need of permission by some autorities of a first-time public introduction/disclosure of certain software/technology, if such authorities for whatever reasons "want" to do so by all means, I am afraid.
Mar 23	comment	Export from US of crypto software with key-size > 56 bits still needs permission? Is it really the case that open-source and free-of-charge alone will exempt from Wassenaar's requirements? I have the same doubts as rath. Could you be kind enough to cite the relevent passages or section numbers of the Wassenaar document?
Mar 20	comment	Security of Deterministic Encryption Scheme @sashank: The link I cited was intended for you to get some useful informations via comparing deterministic with probabilistic (non-deterministic) encryptions. You may also look at Wikipedia's article on deterministic encryption.
Mar 20	comment	Security of Deterministic Encryption Scheme See en.wikipedia.org/wiki/Probabilistic_encryption
Mar 18	comment	Export from US of crypto software with key-size > 56 bits still needs permission? But publishing on the Internet is export to the entire world, including the couple of blacklisted states, isn't it?
Mar 18	comment	Export from US of crypto software with key-size > 56 bits still needs permission? Do I understand you correctly that "strictly" speaking an approval would be needed but "defacto" the authority tolerates the online publications? (I just want to be 100% sure of having correctly understood the issue.)
Mar 3	comment	How to solve the reverse of an equation that uses MOD? @hsikcah: You have r=83172, b=3182, a=380951. b*(a-2)=62135 mod a. So v=r62135=291905 mod a, and v*b=83172=r mod a, as required.
Mar 2	comment	Are there any practical implementation of a homomorphic hashing or signature scheme? @sashank: Note though that I had responded to your original (unedited) OP with a comment and given there a negative answer.
Feb 27	comment	Are there any practical implementation of a homomorphic hashing or signature scheme? As far as I know, there is yet no practically efficient implementation of fully homomorphic encryption on the horizon. So the answer to your question would evidently be negative, at least for a good hashing scheme, IMHO.
Feb 10	comment	Can we replace the XOR operation in DES with some other operation? If xor is used somewhere in encryption, that effect is reversed in decryption with xor. Similarly addition mod 2n can be reversed with subtraction mod 2n. So you could use instead of xor the modular addition. But the result isn't DES and I don't know what severe adverse effects one obtains with that kind of modification to DES.
Feb 6	comment	How to check the strength of an encryption algorithm? See en.wikipedia.org/wiki/Differential_cryptanalysis for the important role played by S-Boxes in DES. In fact the other components are comparatively unessential. In comparison, in AES there are other components that are also essential IMHO.
Feb 6	comment	How to check the strength of an encryption algorithm? @PaŭloEbermann: There have been huge numbers of scientific papers on the security properties of certain S-Boxes, e.g. of DES. So that's "something whose security properties we use when proving properties of higher-level algorithms [here DES]", right? Hence S-Box is a primitive according to your own definition.
Feb 5	comment	How to check the strength of an encryption algorithm? @CodesInChaos: Do you imply that an S-Box isn't a primitive of ciphers? What's your general definition of primitives of ciphers?
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.)