Class String2Key

pgpy/packet/fields.py:727–1057

3.7. String-to-Key (S2K) Specifiers String-to-key (S2K) specifiers are used to convert passphrase strings into symmetric-key encryption/decryption keys. They are used in two places, currently: to encrypt the secret part of private keys in the private keyring, and to convert p

class String2Key(Field):
    """
    3.7.  String-to-Key (S2K) Specifiers

    String-to-key (S2K) specifiers are used to convert passphrase strings
    into symmetric-key encryption/decryption keys.  They are used in two
    places, currently: to encrypt the secret part of private keys in the
    private keyring, and to convert passphrases to encryption keys for
    symmetrically encrypted messages.

    3.7.1.  String-to-Key (S2K) Specifier Types

    There are three types of S2K specifiers currently supported, and
    some reserved values:

       ID          S2K Type
       --          --------
       0           Simple S2K
       1           Salted S2K
       2           Reserved value
       3           Iterated and Salted S2K
       100 to 110  Private/Experimental S2K

    These are described in Sections 3.7.1.1 - 3.7.1.3.

    3.7.1.1.  Simple S2K

    This directly hashes the string to produce the key data.  See below
    for how this hashing is done.

       Octet 0:        0x00
       Octet 1:        hash algorithm

    Simple S2K hashes the passphrase to produce the session key.  The
    manner in which this is done depends on the size of the session key
    (which will depend on the cipher used) and the size of the hash
    algorithm's output.  If the hash size is greater than the session key
    size, the high-order (leftmost) octets of the hash are used as the
    key.

    If the hash size is less than the key size, multiple instances of the
    hash context are created -- enough to produce the required key data.
    These instances are preloaded with 0, 1, 2, ... octets of zeros (that
    is to say, the first instance has no preloading, the second gets
    preloaded with 1 octet of zero, the third is preloaded with two
    octets of zeros, and so forth).

    As the data is hashed, it is given independently to each hash
    context.  Since the contexts have been initialized differently, they
    will each produce different hash output.  Once the passphrase is
    hashed, the output data from the multiple hashes is concatenated,
    first hash leftmost, to produce the key data, with any excess octets
    on the right discarded.

    3.7.1.2.  Salted S2K

    This includes a "salt" value in the S2K specifier -- some arbitrary
    data -- that gets hashed along with the passphrase string, to help