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* pkclist.c (select_algo_from_prefs): Make sure the scores can't

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overflow when picking an algorithm (not a security issue since we
can't pick something not present in all preference lists, but we might
pick something that isn't scored first choice).

* pkclist.c (select_algo_from_prefs): Slightly improve the handling of
MD5 in preference lists.  Instead of replacing MD5 with SHA-1, just
remove MD5 from the list altogether, and let the next-highest ranked
algorithm be chosen.
This commit is contained in:
David Shaw 2010-10-29 19:49:54 +00:00
parent b0b46f46cf
commit b4da5a4150
2 changed files with 43 additions and 17 deletions
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12
g10/ChangeLog
View File

@ -1,3 +1,15 @@
2010-10-29 David Shaw <dshaw@jabberwocky.com>
* pkclist.c (select_algo_from_prefs): Make sure the scores can't
overflow when picking an algorithm (not a security issue since we
can't pick something not present in all preference lists, but we
might pick something that isn't scored first choice).
* pkclist.c (select_algo_from_prefs): Slightly improve the
handling of MD5 in preference lists. Instead of replacing MD5
with SHA-1, just remove MD5 from the list altogether, and let the
next-highest ranked algorithm be chosen.
2010-10-27 Werner Koch <wk@g10code.com>
* keygen.c (ask_expire_interval): Do not print the y2038 if we

48
g10/pkclist.c
View File

@ -1,6 +1,6 @@
/* pkclist.c - create a list of public keys
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007,
* 2008, 2009 Free Software Foundation, Inc.
* 2008, 2009, 2010 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
@ -1303,9 +1303,8 @@ select_algo_from_prefs(PK_LIST pk_list, int preftype,
u32 bits[8];
const prefitem_t *prefs;
int result=-1,i;
unsigned int best=-1;
byte scores[256];
u16 scores[256];
if( !pk_list )
return -1;
@ -1367,7 +1366,13 @@ select_algo_from_prefs(PK_LIST pk_list, int preftype,
{
if( prefs[i].type == preftype )
{
scores[prefs[i].value]+=rank;
/* Make sure all scores don't add up past 0xFFFF
(and roll around) */
if(rank+scores[prefs[i].value]<=0xFFFF)
scores[prefs[i].value]+=rank;
else
scores[prefs[i].value]=0xFFFF;
mask[prefs[i].value/32] |= 1<<(prefs[i].value%32);
rank++;
@ -1434,10 +1439,31 @@ select_algo_from_prefs(PK_LIST pk_list, int preftype,
if(result==-1)
{
unsigned int best=-1;
/* At this point, we have not selected an algorithm due to a
special request or via personal prefs. Pick the highest
ranked algorithm (i.e. the one with the lowest score). */
if(preftype==PREFTYPE_HASH && scores[DIGEST_ALGO_MD5])
{
/* "If you are building an authentication system, the recipient
may specify a preferred signing algorithm. However, the
signer would be foolish to use a weak algorithm simply
because the recipient requests it." (RFC4880:14). If any
other hash algorithm is available, pretend that MD5 isn't.
Note that if the user intentionally chose MD5 by putting it
in their personal prefs, then we do what the user said (as we
never reach this code). */
for(i=DIGEST_ALGO_MD5+1;i<256;i++)
if(scores[i])
{
scores[DIGEST_ALGO_MD5]=0;
break;
}
}
for(i=0;i<256;i++)
{
/* Note the '<' here. This means in case of a tie, we will
@ -1455,18 +1481,6 @@ select_algo_from_prefs(PK_LIST pk_list, int preftype,
result=i;
}
}
/* "If you are building an authentication system, the recipient
may specify a preferred signing algorithm. However, the
signer would be foolish to use a weak algorithm simply
because the recipient requests it." (RFC4880:14). If we
settle on MD5, and SHA1 is also available, use SHA1 instead.
Note that if the user intentionally chose MD5 by putting it
in their personal prefs, then we do what the user said (as we
never reach this code). */
if(preftype==PREFTYPE_HASH && result==DIGEST_ALGO_MD5
&& (bits[0] & (1<<DIGEST_ALGO_SHA1)))
result=DIGEST_ALGO_SHA1;
}
return result;