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17

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 ...


16

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 ...


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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