/****************
* Return -1 if we could not find an algorithm.
*/
int
select_algo_from_prefs(PK_LIST pk_list, int preftype,
int request, const union pref_hint *hint)
{
PK_LIST pkr;
u32 bits[8];
const prefitem_t *prefs;
int i, j;
int compr_hack=0;
int any;
if( !pk_list )
return -1;
memset( bits, ~0, 8 * sizeof *bits );
for( pkr = pk_list; pkr; pkr = pkr->next ) {
u32 mask[8];
memset( mask, 0, 8 * sizeof *mask );
if( preftype == PREFTYPE_SYM ) {
if( PGP2 &&
pkr->pk->version < 4 &&
pkr->pk->selfsigversion < 4 )
mask[0] |= (1<<1); /* IDEA is implicitly there for v3 keys
with v3 selfsigs (rfc2440:12.1) if
--pgp2 mode is on. This doesn't
mean it's actually available, of
course. */
else
mask[0] |= (1<<2); /* 3DES is implicitly there for everyone else */
}
else if( preftype == PREFTYPE_HASH ) {
/* While I am including this code for completeness, note
that currently --pgp2 mode locks the hash at MD5, so this
function will never even be called. Even if the hash
wasn't locked at MD5, we don't support sign+encrypt in
--pgp2 mode, and that's the only time PREFTYPE_HASH is
used anyway. -dms */
if( PGP2 &&
pkr->pk->version < 4 &&
pkr->pk->selfsigversion < 4 )
mask[0] |= (1<<1); /* MD5 is there for v3 keys with v3
selfsigs when --pgp2 is on. */
else
mask[0] |= (1<<2); /* SHA1 is there for everyone else */
}
else if( preftype == PREFTYPE_ZIP )
mask[0] |= (1<<0); /* Uncompressed is implicit */
if (pkr->pk->user_id) /* selected by user ID */
prefs = pkr->pk->user_id->prefs;
else
prefs = pkr->pk->prefs;
any = 0;
if( prefs ) {
for (i=0; prefs[i].type; i++ ) {
if( prefs[i].type == preftype ) {
mask[prefs[i].value/32] |= 1 << (prefs[i].value%32);
any = 1;
}
}
}
if( (!prefs || !any) && preftype == PREFTYPE_ZIP ) {
mask[0] |= 3; /* asume no_compression and old pgp */
compr_hack = 1;
}
#if 0
log_debug("pref mask=%08lX%08lX%08lX%08lX%08lX%08lX%08lX%08lX\n",
(ulong)mask[7], (ulong)mask[6], (ulong)mask[5], (ulong)mask[4],
(ulong)mask[3], (ulong)mask[2], (ulong)mask[1], (ulong)mask[0]);
#endif
for(i=0; i < 8; i++ )
bits[i] &= mask[i];
#if 0
log_debug("pref bits=%08lX%08lX%08lX%08lX%08lX%08lX%08lX%08lX\n",
(ulong)bits[7], (ulong)bits[6], (ulong)bits[5], (ulong)bits[4],
(ulong)bits[3], (ulong)bits[2], (ulong)bits[1], (ulong)bits[0]);
#endif
}
/* usable algorithms are now in bits
* We now use the last key from pk_list to select
* the algorithm we want to use. there are no
* preferences for the last key, we select the one
* corresponding to first set bit.
*/
i = -1;
any = 0;
/* Can we use the requested algorithm? */
if(request>-1 && (bits[request/32] & (1<<(request%32))) &&
algo_available(preftype,request,hint))
return request;
/* If we have personal prefs set, use them instead of the last key */
if(preftype==PREFTYPE_SYM && opt.personal_cipher_prefs)
prefs=opt.personal_cipher_prefs;
else if(preftype==PREFTYPE_HASH && opt.personal_digest_prefs)
prefs=opt.personal_digest_prefs;
else if(preftype==PREFTYPE_ZIP && opt.personal_compress_prefs)
prefs=opt.personal_compress_prefs;
if( prefs ) {
for(j=0; prefs[j].type; j++ ) {
if( prefs[j].type == preftype ) {
if( (bits[prefs[j].value/32] & (1<<(prefs[j].value%32))) ) {
if( algo_available( preftype, prefs[j].value, hint ) ) {
any = 1;
i = prefs[j].value;
break;
}
}
}
}
}
if( !prefs || !any ) {
for(j=0; j < 256; j++ )
if( (bits[j/32] & (1<<(j%32))) ) {
if( algo_available( preftype, j, hint ) ) {
i = j;
break;
}
}
}
#if 0
log_debug("prefs of type %d: selected %d\n", preftype, i );
#endif
if( compr_hack && !i ) {
/* selected no compression, but we should check whether
* algorithm 1 is also available (the ordering is not relevant
* in this case). */
if( bits[0] & (1<<1) )
i = 1; /* yep; we can use compression algo 1 */
}
/* "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." RFC2440:13. If we settle on MD5, and
SHA1 is also available, use SHA1 instead. Of course, if the
user intentionally chose MD5 (by putting it in their personal
prefs), then we should do what they say. */
if(preftype==PREFTYPE_HASH &&
i==DIGEST_ALGO_MD5 && (bits[0] & (1<<DIGEST_ALGO_SHA1)))
{
i=DIGEST_ALGO_SHA1;
if(opt.personal_digest_prefs)
for(j=0; prefs[j].type; j++ )
if(opt.personal_digest_prefs[j].type==PREFTYPE_HASH &&
opt.personal_digest_prefs[j].value==DIGEST_ALGO_MD5)
{
i=DIGEST_ALGO_MD5;
break;
}
}
return i;
}
/****************
* Return -1 if we could not find an algorithm.
*/
int
select_algo_from_prefs(PK_LIST pk_list, int preftype,
int request, const union pref_hint *hint)
{
PK_LIST pkr;
u32 bits[8];
const prefitem_t *prefs;
int result=-1,i;
u16 scores[256];
if( !pk_list )
return -1;
memset(bits,0xFF,sizeof(bits));
memset(scores,0,sizeof(scores));
for( pkr = pk_list; pkr; pkr = pkr->next )
{
u32 mask[8];
int rank=1,implicit=-1;
memset(mask,0,sizeof(mask));
switch(preftype)
{
case PREFTYPE_SYM:
/* IDEA is implicitly there for v3 keys with v3 selfsigs if
--pgp2 mode is on. This was a 2440 thing that was
dropped from 4880 but is still relevant to GPG's 1991
support. All this doesn't mean IDEA is actually
available, of course. */
if(PGP2 && pkr->pk->version<4 && pkr->pk->selfsigversion<4)
implicit=CIPHER_ALGO_IDEA;
else
implicit=CIPHER_ALGO_3DES;
break;
case PREFTYPE_HASH:
/* While I am including this code for completeness, note
that currently --pgp2 mode locks the hash at MD5, so this
code will never even be called. Even if the hash wasn't
locked at MD5, we don't support sign+encrypt in --pgp2
mode, and that's the only time PREFTYPE_HASH is used
anyway. -dms */
/* MD5 is there for v3 keys with v3 selfsigs when --pgp2 is
on. */
if(PGP2 && pkr->pk->version<4 && pkr->pk->selfsigversion<4)
implicit=DIGEST_ALGO_MD5;
else
implicit=DIGEST_ALGO_SHA1;
break;
case PREFTYPE_ZIP:
/* Uncompressed is always an option. */
implicit=COMPRESS_ALGO_NONE;
}
if (pkr->pk->user_id) /* selected by user ID */
prefs = pkr->pk->user_id->prefs;
else
prefs = pkr->pk->prefs;
if( prefs )
{
for (i=0; prefs[i].type; i++ )
{
if( prefs[i].type == preftype )
{
/* 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++;
/* We saw the implicit algorithm, so we don't need
tack it on the end ourselves. */
if(implicit==prefs[i].value)
implicit=-1;
}
}
}
if(rank==1 && preftype==PREFTYPE_ZIP)
{
/* If the compression preferences are not present, they are
assumed to be ZIP, Uncompressed (RFC4880:13.3.1) */
scores[1]=1; /* ZIP is first choice */
scores[0]=2; /* Uncompressed is second choice */
mask[0]|=3;
}
/* If the key didn't have the implicit algorithm listed
explicitly, add it here at the tail of the list. */
if(implicit>-1)
{
scores[implicit]+=rank;
mask[implicit/32] |= 1<<(implicit%32);
}
for(i=0;i<8;i++)
bits[i]&=mask[i];
}
/* We've now scored all of the algorithms, and the usable ones have
bits set. Let's pick the winner. */
/* The caller passed us a request. Can we use it? */
if(request>-1 && (bits[request/32] & (1<<(request%32))) &&
algo_available(preftype,request,hint))
result=request;
if(result==-1)
{
/* If we have personal prefs set, use them. */
prefs=NULL;
if(preftype==PREFTYPE_SYM && opt.personal_cipher_prefs)
prefs=opt.personal_cipher_prefs;
else if(preftype==PREFTYPE_HASH && opt.personal_digest_prefs)
prefs=opt.personal_digest_prefs;
else if(preftype==PREFTYPE_ZIP && opt.personal_compress_prefs)
prefs=opt.personal_compress_prefs;
if( prefs )
for(i=0; prefs[i].type; i++ )
{
if(bits[prefs[i].value/32] & (1<<(prefs[i].value%32))
&& algo_available( preftype, prefs[i].value, hint))
{
result = prefs[i].value;
break;
}
}
}
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
favor the lower algorithm number. We have a choice
between the lower number (probably an older algorithm
with more time in use), or the higher number (probably a
newer algorithm with less time in use). Older is
probably safer here, even though the newer algorithms
tend to be "stronger". */
if(scores[i] && scores[i]<best
&& (bits[i/32] & (1<<(i%32)))
&& algo_available(preftype,i,hint))
{
best=scores[i];
result=i;
}
}
}
return result;
}
