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Aug
12
comment SHACAL in SHA-256
Very good answer. There are two additional advantages of SHACAL-2, I would like to highlight: First: On small microprocessors it could be desirable to implement just one function. It is easy to implement just SHACAL-2 and use it for hash and block cipher. Secondly: On some platforms it is hard to implement AES efficiently without timing side channel. SHACAL-2, on the other hand, is commonly easy to implement without timing side channel.
Jul
18
comment How vulnerable is the C rand() in public cryptography protocols?
There are practically no rand() implementations which would give random numbers useful in cryptographic applications no matter how many bits are skipped. So it is incorrect to claim somebody could adopt rand() for cryptographic purposes.
Jul
3
comment SHA256 output to 0-99 number range?
I have tested all possible SHA-256 hashes which are larger than $100\lfloor \frac {2^{256}}{100}\rfloor$. None of them produce number larger than $100\lfloor \frac {2^{256}}{100}\rfloor$ when hashed the second time. However, double hashing does not remove the bias, the biased numbers are just different.
Jul
3
comment Public and Private key encryption in simple math
RSA algorithm is explained pretty well at RSA Algorithm. It contains both example with small numbers (suitable for calculator) and large numbers. Even with simple numbers it's more convenient if you have advanced calculator as operations common in discrete mathematics are not found on simple calculators. However, RSA with insecurely small numbers is possible to calculate using mental arithmetic.
Jun
13
comment Given $n$ bits, how many “truly random” sequences/numbers can be constructed?
Program "ent" (available on e.g. many lines) uses various algorithms to statistically estimate entropy. Maybe it has some tests you'd like, but as mentioned already, it is not possible to be able to tell for sure (maybe deterministic sequence just looks random or random sequence is randomly looking very deterministic).
Jun
12
awarded  Nice Answer
May
31
comment Creating a license system based on asymmetric encryption (RSA or ECDSA)
For scenario #4, approach that is simple and has been used in practice is whitelisting. Note: The whitelist can get very large.
May
27
awarded  Custodian
May
19
comment Why is XOR preferred over XNOR?
ARMv8 has EON instruction. SPARC has XNOR instruction. Then again, few other processors have it.
May
9
comment Regain 3DES ECB key, assuming I have both encrypted and decrypted text
There are $2^{168}$ possible keys for 24 byte 3DES. It is possible to attack such key with around $2^{112}$ steps, which saves time compares to brute forcing all the possible keys. (But it is still unpractical.)
May
4
revised How do I produce a stream of secure random numbers from AES-Counter mode?
Added a few details to ensure the answer is not reference only.
May
4
answered How do I produce a stream of secure random numbers from AES-Counter mode?
May
4
answered Difference between a nonce and IV
May
3
answered Are ZKPPs possible with server-side hashed passwords?
May
3
awarded  Custodian
May
3
reviewed Leave Closed Is it true, that non-military cryptography appeared in 50's and 60's only thanks to leaks from the NSA?
May
3
comment HMAC-SHA1 vs HMAC-SHA256 for data storage
In encrypted data storage, it is wise to choose the algorithms according to how long the data is to remain cryptographically protected (such as confidentiality or integrity protected). However, it is generally possible to upgrade integrity protection of stored data: just recalculate all macs using a stronger algorithm. Various recommendations (such as NIST) would allow HMAC-SHA1 to be used for data stored up-to (and somewhat beyond) 2030. For data protected longer period of time, something else such as HMAC-SHA256 is good pick, to prevent the need to "upgrade" algorithm during storage period.
May
2
comment About using mistakes as part of a code
@user128932: navajo code talkers was a success in using simple word substitution cipher. And it can be assumed that some experts tried to decode the messages. But that was several decades ago.
Apr
30
comment Can XEX or XTS modes be used with only one tweak?
Word safe is ambiguous. Please, define in more detail what is your intended security model.
Apr
27
comment How to specify a NIST SP 800-108 KBKDF
@owlstead: Have you taken a look at the scheme for describing the contents of test vectors, given in KBKDFVS? It describes a lot about the usage of the KDF. I improved my answer to cover that.