340 reputation
18
bio website
location
age
visits member for 2 years, 1 month
seen 2 days ago

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
10
asked Any historical accounts of cryptanalysis of Jefferson's wheel cipher?
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?
@PaĆ­loEbermann: 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.)
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