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11h
comment RSA : Double-Encryption and order of Encryption
I suppose the context is encryption processing using keys of both the receiver and the sender, i.e. receiver's public key with modulus MR and sender's secret key with modulus MS. Since RSA processing with a modulus M results in numbers in [0, 2**M-1], the double processing is only sensible when the first processing uses a modulus that is the smaller one of MR and MS , for otherwise there could be truncations. (Whether this double processing is what one desires is another matter.)
Jan
29
comment When we use permutation and random long sting to hide a message
But you could give a concrete trivial (may be no good for your intended purposes) example such that one clearly knows your underlying thought. Say, the English name is "Eve", the random string is ........(your choice), assuming that case is ignored.
Jan
29
comment When we use permutation and random long sting to hide a message
I may gravely err, but I surmise that your question might not be "well-formed". For (in any case) the random string could have a subset of size 30 that forms a valid English name also of size 30. Now, which one is the "right" name to be found? I suggest that you illustrate your idea through highly reducing the sizes, giving a concrete example with a short English name and a corresponding short random string such that your question could be clearly understood.
Jan
28
comment AES key and block size
@Maarten Bodewes: P.20 of FIPS-197 has "Figure 11 Pseudo Code for Key Expansion" and also notes that its "Appendix A presents examples of Key Expansion".
Jan
27
comment Implementing cryptosystems with various programming langauges
My personal view is highly biased. I don't know Agda, but from the little I know in general about PLs that let you do proofs they demand very much mental efforts of the programmer. However, C/C++ are IMHO too verbose, such that it is frequently not easy/efficient in code reviews to compare with the flow of the underlying ideas of the algorithms being implemented. I would say that it may be a good idea to forgo proofs and instead to first do a full implementation in a compact, less efficient PL like Python and after a thorough review do, if needed, "comparable" implementatons in efficient PLs.
Jan
27
comment history of non secret cryptograph
It would be fine, if you could provide a reference to that (historical) existence proof.
Jan
27
comment AES key and block size
Then that's well specified in the standard document FIPS-197 of NIST, where the processing of the AES scheme is nicely described with pseudo-codes. For a concrete implementation in Python that closely follows that, see: s13.zetaboards.com/Crypto/topic/7385224/1
Jan
26
comment Is there any more information on this RSA backdoor?
The indicated type of backdoors means that the malice has only to factor n' = p'*q', whose size is 1/4 of that of the ("official") modulus n. He could thus succeed, if n is not too large (not if n is, say, of 8K bits.) BTW, IMHO more easily the malice could appropriately employ PRNGs to build a backdoor such that the n generated has always a factor that is in a (sufficiently large) set of moduli known to him. (I mentioned this in security.stackexchange.com/questions/109776/… )
Jan
26
comment Q: Relevance of physical layer security to cryptography
I am not yet sure. If I don't err,. the said field principally considers the fact that the actual physical channel is noisy and somehow exploits that noisiness to achieve secure transmission of keys etc.
Jan
25
comment Is there any more information on this RSA backdoor?
A type of feasible highly sophisticated RSA backdoor in non-open-source software that IMHO is not detectable at all by outsiders is due to maartin many years ago and is recently elaborated by me at the end of the Epilogue section of s13.zetaboards.com/Crypto/topic/7234475/1
Jan
19
comment splitting the plaintext and ciphertext into blocks
Everything that can be done with a computer can "in principle" also be done manually but in the overwhelming majority of cases impossible in practice due to the huge time required and limitations of the other resources available. RSA is namely a modern crypto algorithm, not a classical one like e.g. Vigenere or Playfair. (Of course, if you just want to "play" with the modern stuffs, you could in many cases reduce the sizes of the parameters of the algorithms to sufficiently small ones such that your could work with paper and pencil without thereby committing mistakes.)
Jan
18
comment splitting the plaintext and ciphertext into blocks
I employ RSA to encrypt blocks of plaintext in the common sense of chained block encrpytion with integrity check. See Example 3 in Appendix of my code: s13.zetaboards.com/Crypto/topic/7234475/1
Jan
16
comment Can a book cipher be cracked without key?
I suppose it cound be fairly advantageous to simply postprocess the ciphertext from a book cipher with a transposition in the classical sense such that the user's manual work would be hard to analyze even with resources comparable to that of Google.
Jan
12
comment References for cascade
In classical crypto, combining transposition and substitution processing is generally a good idea IMHO.
Jan
9
comment What are the main weaknesses of a Playfair cipher, if any?
Merely a side comment: The weakness of Playfair as pointed out in the answers could be somewhat compensated by combining Playfair with transpositions, e.g. columnar transpositions.
Jan
6
comment NIST tests for AES
@RichieFrame: What is in Appendix C of FIPS 197 is simply known results of certain test vectors. Hence it is a simple comparison to be done by the implementor. What is in AVS is however very much more comprehensive and requires some coding to be written carefully.
Jan
5
comment NIST tests for AES
Sec. 6.1 of the document says: "To initiate the validation process of the AESAVS, a vendor submits an application to an accredited laboratory requesting the validation of their implementation of the algorithm specified in FIPS 197 ...". This means IMHO that an officially trusted laboratory is to (independently) certify the correctness of an implementation. If the implementer himself writes such a test suite there wouldn't be independence and the result would remain uncertain. (Analogy: In normal programming one could write one's own test codes but often risks to oversee one's own mistakes.)
Jan
5
comment NIST tests for AES
Standard conformity test of AES implementations can be easily done according to Appendix C of FIPS-197. In case you have problems with that, you could compare with my Python coding of AES (s13.zetaboards.com/Crypto/topic/7385224/1/) where the test is performed with the function checkencryptionwithfips197().
Jan
2
comment When/why is RSA (hybrid) encryption used rather than alternatives?
@fgrieu: I completely agree with you. But I merely called attention to the fact that not all applications require extremely high processing speeds. Anyway I interpreted the title of samoz's OP to mean that he desired some simple convenient way to encrypt certain arbitrary long personal messages with RSA alone. In that case, even with an interpreted language like Python, my own coding experience is that cpu time of the order of 1 sec is easily achievable.
Dec
30
comment When/why is RSA (hybrid) encryption used rather than alternatives?
In contrast to your 1st paragraph, I deem desiderata of the genre of the title line of samoz's thread to be principally justified from the perspective of software engineering. For, if a software depends on more than one algorithm (i.e. hybrid schemes), then one would have troubles, if one of the algorithms happens later to encounter security problems, while, if it depnends only on a single algorithm, the number of worries in the life cycle of the software is anyway minimized. Overall, I consider processing efficiency less important than simplicity and ease of understanding and maintenance.