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pgcrypto: support changing S2K iteration count

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pgcrypto already supports key-stretching during symmetric encryption,
including the salted-and-iterated method; but the number of iterations
was not configurable.  This commit implements a new s2k-count parameter
to pgp_sym_encrypt() which permits selecting a larger number of
iterations.

Author: Jeff Janes
This commit is contained in:
Alvaro Herrera
2016-03-09 14:31:07 -03:00
parent b6fb6471f6
commit 188f359d39
9 changed files with 98 additions and 16 deletions
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37
contrib/pgcrypto/pgp-s2k.c
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@ -132,12 +132,10 @@ calc_s2k_iter_salted(PGP_S2K *s2k, PX_MD *md, const uint8 *key,
unsigned preload = 0;
unsigned remain,
c,
cval,
curcnt,
count;
cval = s2k->iter;
count = ((unsigned) 16 + (cval & 15)) << ((cval >> 4) + 6);
count = s2k_decode_count(s2k->iter);
md_rlen = px_md_result_size(md);
@ -195,21 +193,34 @@ calc_s2k_iter_salted(PGP_S2K *s2k, PX_MD *md, const uint8 *key,
}
/*
* Decide S2K_ISALTED iteration count
* Decide PGP_S2K_ISALTED iteration count (in OpenPGP one-byte representation)
*
* Too small: weak
* Too big: slow
* gpg defaults to 96 => 65536 iters
* let it float a bit: 96 + 32 => 262144 iters
*
* For our default (count=-1) we let it float a bit: 96 + 32 => between 65536
* and 262144 iterations.
*
* Otherwise, find the smallest number which provides at least the specified
* iteration count.
*/
static int
decide_count(unsigned rand_byte)
static uint8
decide_s2k_iter(unsigned rand_byte, int count)
{
return 96 + (rand_byte & 0x1F);
int iter;
if (count == -1)
return 96 + (rand_byte & 0x1F);
/* this is a bit brute-force, but should be quick enough */
for (iter = 0; iter <= 255; iter++)
if (s2k_decode_count(iter) >= count)
return iter;
return 255;
}
int
pgp_s2k_fill(PGP_S2K *s2k, int mode, int digest_algo)
pgp_s2k_fill(PGP_S2K *s2k, int mode, int digest_algo, int count)
{
int res = 0;
uint8 tmp;
@ -219,19 +230,19 @@ pgp_s2k_fill(PGP_S2K *s2k, int mode, int digest_algo)
switch (s2k->mode)
{
case 0:
case PGP_S2K_SIMPLE:
break;
case 1:
case PGP_S2K_SALTED:
res = px_get_pseudo_random_bytes(s2k->salt, PGP_S2K_SALT);
break;
case 3:
case PGP_S2K_ISALTED:
res = px_get_pseudo_random_bytes(s2k->salt, PGP_S2K_SALT);
if (res < 0)
break;
res = px_get_pseudo_random_bytes(&tmp, 1);
if (res < 0)
break;
s2k->iter = decide_count(tmp);
s2k->iter = decide_s2k_iter(tmp, count);
break;
default:
res = PXE_PGP_BAD_S2K_MODE;