Mok-Kong Shen
  • Member for 9 years, 4 months
  • Last seen more than 4 years ago
How were semagrams encrypted in the pre-digital era?
4 votes

There was a telegraphic code that mapped the comparatively frequently used 10000 words (that's very much more than for common daily use, e.g. newspapers) of Chinese to [0,9999]. There was once also a ...

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Any efficient text-based steganographic schemes?
4 votes

In his answer Michael mentioned a known stego scheme of using the first characters of words/sentences as stego characters and rightly remarked that the scheme can be practically applied ("user-...

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One time pad key exchange
4 votes

That's a well-known disadvantage of using OTP. Like in the ancient times, you could e.g. employ a trusted courier for that transfer.

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How to convert a set of sequential integers into a set of unique random numbers?
3 votes

The algorithm of Fisher and Yates (see Knuth, The Art of Computer Programming, vol. 2) does a pseudo-random permutation of a sequence without however avoiding possible duplicates in your sense. One ...

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Secure CSPRNG's for cryptographic keys
3 votes

LFSR as such isn't a CSPRNG. There are diverse CSPRNGs, see crypto textbooks, also A. Menezes et al., Handbook of Applied Cryptography (freely available online). I have a code for a CSPRNG based on ...

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How can I generate large prime numbers for RSA?
3 votes

Instead of using probabilistic methods to generate large primes, as indicated in the other answers, one can (IMHO better) employ Maurer's algorithm of generating provable primes. I have a Python code ...

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Updating the seed key of a PRNG while maintaining initial entropy?
Accepted answer
3 votes

It's a matter of periods in the sequence of numbers generated by the PRNG. If the output of the PRNG has a single period that is of length $2^n$, then you can avoid repetition by appropriately ...

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Hill Cipher question
3 votes

You would need (at least) 3 pairs of vectors in order to determine the 3*3 matrix.

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What is a block cipher?
3 votes

As its name indicates, a block cipher is an algorithm to encrypt (with a secret key) plaintexts in chunks of a certain fixed block size. For practical reasons, software of a block cipher has only one ...

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RotWord in Rijndael's Algorithm
Accepted answer
2 votes

Yes. See also en.wikipedia.org/wiki/Advanced_Encryption_Standard. There is a pseudo-code in NIST's AES standard document which is very helpful for implementors. I have a Python code that very closely ...

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What is the most computationally efficient way of generating pseudo-random permutations?
2 votes

The theoretically correct random permutation algorithem is IMHO uniquely that of Fisher and Yates [1], which needs for performing a permutation of a sequence of n items n-1 PRNs. I perviously found ...

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Is there an algorithm to hide text in another text, while preserving the meaning of the latter?
1 votes

I have a very simple code of doing steganography that neither modifies any word of your original text nor poses any constraints on the words you employ in the text; it simply changes a little bit of ...

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Is there any tool for text steganography?
Accepted answer
1 votes

Text steganography is by nature more difficult to do than image steganography, if high security is demanded. For good results one has to accept the trade-off of lower stego bit-rates, which could be ...

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RC6 Key Size Understanding
1 votes

[Copy of my answer in another community:] In the RC6 specification (see de.wikipedia.org/wiki/RC6) S[*] designates an array of 2r+4 round keys, whose size in bits you can choose in the range [0,2000]. ...

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Deriving Keys for Symmetric Encryption and Authentication
1 votes

Since a good block encryption algorithm, e.g. AES, running in counter mode, i.e. encrypting some more or less arbitrary chosen (unknown to the opponent) input values, is generally considered to be ...

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Is it possible for Alice and Bob to both sign a message "simultaneously"?
0 votes

When a contract in digital from is to be signed online by Alice and Bob, an issue concerning the fairness of the signing process crops up as follows: If Alice first signs the document and sends it to ...

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Are there any practical methods of steganography?
0 votes

I devised a (presumably non-conventional) scheme which re-formats an input text stream like emails a little bit such that the number of words in a line of the output file mod 2 gives the stego bit in ...

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Which method to generate one time password?
0 votes

I suppose you could use the initial passphrase as the key of a block cipher to encrypt a session dependent non-secret data, e.g. date and message serial number etc., and use that for your purpose.

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How are primes generated for RSA?
0 votes

I have implemented Maurer's algorithm of generating random provable primes (see Menezes et al., Handbook of Applied Cryptography) in Python, which is, as comparison showed, only moderately slower than ...

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How are random numbers for RSA generated?
0 votes

Maurer has an algorithm to generate random, almost uniformly distributed, k-bit primes that are provably prime, in contrast to schemes that generate highly probably primes (commonly employing the ...

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How to better generate large primes: sieving and then random picking or random picking and then checking?
0 votes

A. J. Menezes et al., Handbook of Applied Cryptography (available online) 4.62 gives Maurer's algorithm for generating provable primes, which is fairly competitive in runtime with probabilistic ...

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Export from US of crypto software with key-size > 56 bits still needs permission?
0 votes

Taking the advice of @rath, I asked EFF with the question formulated in my comment to his post with the addition whether the US scientists doing online crypto publications could, at time points ...

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