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Jan
3
answered Uniformly distributed secure floating point numbers in [0,1)
Jan
2
answered Continuous stream of strong randomness from limited entropy?
Jan
2
comment What is the difference between key size and block size (for AES)
I'm not 100% sure what you're trying to ask here, but I am pretty sure that, whatever it is, it's probably too broad to be effectively answerable here. You might want to start by picking up an introductory book on cryptography, which should explain how block ciphers like AES work, and how they can and should be used.
Dec
30
comment Is there such a thing as a hash function with a fixed size input?
Technically, any standard hash function can be made into one that takes a fixed-size input, simply by restricting its inputs to a specific size.
Dec
30
comment Encrypting passwords
Generally, encrypting passwords is not a good idea. Do you need to store the passwords to automatically authenticate the user to some external service (i.e. are you implementing something like a "password wallet"), or are you just using the passwords to grant the user access to your app? If the latter, you shouldn't be encrypting the passwords at all, but rather hashing them; if the former, can you switch to some other (e.g. public key based) authentication method?
Dec
29
reviewed Close How secure is 'Plain Old RSA'
Dec
29
reviewed Leave Open Modular exponentiation on calculator for textbook RSA
Dec
29
revised Modular exponentiation on calculator for textbook RSA
copyedit, code formatting
Dec
29
comment RSA by hand - did I do something wrong? (c = m on encryption)
Related: For which RSA moduli, precisely, is $e=d$ for all $e$?
Dec
28
comment What algorithm to use to rotate values in a predefined manner and be able to decrypt them back to the original?
My suggestion above would be to use the block cipher directly to encrypt individual blocks; your crypto library probably exposes that as "ECB mode", which takes no IV / nonce, and treats the plaintext / ciphertext as a series of individual cipher blocks to be encrypted / decrypted separately. (ECB mode is not a general-purpose semantically secure encryption mode by itself, but the raw access it provides to the block cipher is useful e.g. for implementing other modes, or for custom cryptographic schemes like this.)
Dec
28
comment Shamir's Secret Scheme : Knowing the threshold
Not as far as I can see. But maybe we're thinking of different scenarios. I was talking about adding one extra share to a set of $k$ shares, i.e. going from a polynomial of order (at most) $k-1$ to one of order (at most) $k$. By construction, these polynomials intersect at the $k$ original shares; if they intersect anywhere else, they must be identical.
Dec
28
comment Shamir's Secret Scheme : Knowing the threshold
Take the interpolated polynomial for the $k$ shares, and evaluate it at the $x$-coordinate of the new share. There's a $1/q$ chance that the result will match the $y$-coordinate of the share, in which case adding the extra share will not alter the polynomial.
Dec
28
answered Autocorrelation in Autokey
Dec
28
answered Information theoretical security of an inefficient Shamir based access structure
Dec
28
comment Information theoretical security of an inefficient Shamir based access structure
OK, I think I can follow your notation now. You might want to edit that information into the question itself, though.
Dec
28
comment Shamir's Secret Scheme : Knowing the threshold
+1, but do note that you can't ever be sure that you've collected enough shares; assuming that the original polynomial coefficients have been chosen randomly, for every set of $k < t$ shares there's a $1/q$ chance that adding one more share to a set of $k$ shares will not change the reconstructed polynomial, where $q$ is the number of elements in the field you're using. (You can tweak the coefficients to avoid this, at least to some extent, but this introduces bias and can thus potentially leak information about the secret to groups with less than $t$ shares.)
Dec
28
comment Information theoretical security of an inefficient Shamir based access structure
It might be easier to understand (and answer) your question if you started it by telling us just what, exactly, your scheme is supposed to accomplish (i.e. allow legitimate users to do, and prevent attackers from doing).
Dec
27
answered What algorithm to use to rotate values in a predefined manner and be able to decrypt them back to the original?
Dec
27
answered How should I generate secure random numbers deterministically?
Dec
24
revised Koblitz encoding a message to a point, what is the “associated auxiliary base parameter”?
move extra info from comments to answer