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comment How many bits of entropy can I expect from /dev/urandom in iOS?
Once you've collected, say, 256 bits of entropy, you can use that to generate essentially arbitrary amounts of pseudorandom bits that are secure for all practical purposes. CTR_DRBG is a perfectly good way to go about doing this. Concerns over "running out" of entropy are misplaced. Others have put it more elegantly than I can: gist.github.com/tarcieri/6347417, sockpuppet.org/blog/2014/02/25/safely-generate-random-numbers
1d
reviewed Close Executing encrypted code?
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reviewed Close Product of Sophie Germain Primes and safe primes
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comment Product of Sophie Germain Primes and safe primes
I'm voting to close this question as off-topic because it does not ask a question about cryptography.
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reviewed Approve perfect-secrecy tag wiki excerpt
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reviewed Approve error-propagation tag wiki excerpt
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reviewed Approve memory-hard tag wiki excerpt
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comment Encrypt-Mix-Encrypt: Full Diffusion?
There were originally some patent issues (which may or may not have been resolved since, I haven't seen anything definitive). Additionally, EME requires two blockcipher calls per block of input, which slows performance.
2d
answered Encrypt-Mix-Encrypt: Full Diffusion?
May
20
comment Would this method deliver a perfectly non-malleable encryption for at least two blocks?
@Anon2000, First, as Steven says, you probably should be looking for a MAC. But if you're really after non-malleable encryption, then what you want is a wide-block cipher, such as EME or the more recent AEZ with a zero-bit tag and zero-bit nonce (web.cs.ucdavis.edu/~rogaway/aez).
May
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reviewed Close where should private and public keys be stored?
May
3
comment Format preserving encryption FFX
@MaartenBodewes Yes. I edited my answer to expand the acronym out.
May
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revised Format preserving encryption FFX
expanded TPRP acronym
May
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revised Format preserving encryption FFX
Typo fixes
May
2
answered Format preserving encryption FFX
Apr
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reviewed Close Decrypt files with original file CTB-Locker
Apr
3
comment Required key size for an ideal cipher with a 32 bit block size
I suspect this is a homework question aimed at establishing why we can't construct an ideal cipher for even modest block sizes. asdfhjk: For a cipher to be ideal, you need one key for each possible permutation. So how many strings are in the set {0, 1}^32? How many permutations are there on a set of this size?
Mar
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awarded  Custodian
Mar
31
reviewed No Action Needed What happens when a RC4 stream gets corrupted?
Mar
31
reviewed No Action Needed What can cause similar MD5 hashes