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17

OpenPGP's "Iterated and Salted S2K" is just a single hash instance over a very long input, which consists in the repeated concatenation of the salt and the password. This is extremely GPU-friendly, especially when using a hash function which is built over 32-bit elementary operations (this category includes MD5, SHA-1, SHA-256 and RIPEMD-160; GPU are not as ...


16

The "s2k" options correspond to the String-to-Key specifiers. An s2k transform turns a human-compatible symmetric secret (a password or passphrase) into a symmetric key suitable for a symmetric encryption or MAC algorithm. Turning passwords into keys is tricky business because passwords that human can remember and accept to type tend to be weak with regards ...


3

s2k = "string to key", so a password is transformed into a key for a symmetric cipher. It's documented in RFC4880. The "count" is the number of bytes hashed in each hashing step, which is only relevant for the most secure and default s2k-version, salted and iterated.


2

s2kcount is an iteration count for the "string to key" (s2k) algorithm used, which would be algorithm for converting a password into an appropriate length key. This iteration count should be "high" -- in many applications it's chosen automatically and so that a significant amount of CPU time is needed for s2k, say between 0.1 to 1 second. What is correct ...


2

Short answer: public exponent $65537$, certainty $5$. Terms and Conditions May Apply. I have no clues about string to key count. Whenever one wants to know " what values are appropriate ", there's the problem of defining appropriate: is there some normative context, e.g. FIPS 186-4? I'll assume that reference. This, and all standards I know,...


2

Most hash functions ( it appears this includes S2k) are not memory intensive. As such you can run a bunch of computations of their iterated variants on a GPU very cheaply. Scrypt, however, is designed to be memory intensive, so you can't really run it effectively in parallel without huge memory requirements.


2

(1,2) You could use: gpg2 --s2k-mode 3 --s2k-count 65011712 --s2k-digest-algo SHA512 --s2k-cipher-algo AES256 --symmetric /*file path* According to The GNU Privacy Guard Manual, p. 71, we use --s2k-cipher-algo name when we want to apply symmetric encryption with a passphrase if --cipher-algo name or --personal-cipher-preferences string have not been set. ...


1

Yes, it's still talking about the case where multiple hashes are needed to get to the key size. Such a function is called a key expand function. It explains that they are taken independently (different contexts) over the passphrase (the data). A different context means that the calls to the hash functions don't interact; $H$ is seen as a single call to a ...


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