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gpg: Improve API documentation.

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* g10/seskey.c (make_session_key): Improve documentation.
(encode_session_key): Improve documentation.
* g10/encrypt.c (encrypt_seskey): Remove gratuitous initialization.
* g10/dek.h (DEK): Improve documenation.

--
Signed-off-by: Neal H. Walfield <neal@g10code.com>
This commit is contained in:
Neal H. Walfield 2016-02-03 14:23:51 +01:00
parent 5cdde08ea8
commit 9663b08848
3 changed files with 24 additions and 13 deletions
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28
g10/seskey.c
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@ -31,9 +31,11 @@
#include "i18n.h"
/****************
* Make a session key and put it into DEK
*/
/* Generate a new session key in *DEK that is appropriate for the
algorithm DEK->ALGO (i.e., ensure that the key is not weak).
This function overwrites DEK->KEYLEN, DEK->KEY. The rest of the
fields are left as is. */
void
make_session_key( DEK *dek )
{
@ -67,11 +69,12 @@ make_session_key( DEK *dek )
}
/****************
* Encode the session key. NBITS is the number of bits which should be used
* for packing the session key.
* returns: A mpi with the session key (caller must free)
*/
/* Encode the session key stored in DEK as an MPI in preparation to
encrypt it with the public key algorithm OPENPGP_PK_ALGO with a key
whose length (the size of the public key) is NBITS.
On success, returns an MPI, which the caller must free using
gcry_mpi_release(). */
gcry_mpi_t
encode_session_key (int openpgp_pk_algo, DEK *dek, unsigned int nbits)
{
@ -136,14 +139,15 @@ encode_session_key (int openpgp_pk_algo, DEK *dek, unsigned int nbits)
log_bug ("can't encode a %d bit key in a %d bits frame\n",
dek->keylen*8, nbits );
/* We encode the session key in this way:
/* We encode the session key according to PKCS#1 v1.5 (see section
* 13.1.1 of RFC 4880):
*
* 0 2 RND(n bytes) 0 A DEK(k bytes) CSUM(2 bytes)
* 0 2 RND(i bytes) 0 A DEK(k bytes) CSUM(2 bytes)
*
* (But how can we store the leading 0 - the external representaion
* of MPIs doesn't allow leading zeroes =:-)
*
* RND are non-zero random bytes.
* RND are (at least 1) non-zero random bytes.
* A is the cipher algorithm
* DEK is the encryption key (session key) length k depends on the
* cipher algorithm (20 is used with blowfish160).
@ -154,6 +158,8 @@ encode_session_key (int openpgp_pk_algo, DEK *dek, unsigned int nbits)
n = 0;
frame[n++] = 0;
frame[n++] = 2;
/* The number of random bytes are the number of otherwise unused
bytes. See diagram above. */
i = nframe - 6 - dek->keylen;
assert( i > 0 );
p = gcry_random_bytes_secure (i, GCRY_STRONG_RANDOM);