* sign.c (hash_for, sign_file): When encrypting and signing at the same

time, consult the various hash prefs to pick a hash algorithm to use.
Pass in a 160-bit hint if any of the signing keys are DSA.

* keydb.h, pkclist.c (select_algo_from_prefs, algo_available): Pass a
"hints" opaque pointer in to let the caller give hints as to what
algorithms would be acceptable.  The only current hint is for
PREFTYPE_HASH to require a 160-bit hash for DSA.  Change all callers in
encode.c (encode_crypt, encrypt_filter) and sign.c (sign_file).  If we
settle on MD5 as the best algorithm based solely on recepient keys and
SHA1 is also a possibility, use SHA1 unless the user intentionally chose
MD5.  This is as per 2440:13.

* exec.c (make_tempdir): Fix duplicated filename problem.

6 files changed, 115 insertions, 20 deletions

diff --git a/g10/ChangeLog b/g10/ChangeLog
index b9e82eae4..cdc62aa35 100644
--- a/g10/ChangeLog
+++ b/g10/ChangeLog
@@ -1,3 +1,21 @@
+2002-06-04  David Shaw  <[email protected]>
+
+	* sign.c (hash_for, sign_file): When encrypting and signing at the
+	same time, consult the various hash prefs to pick a hash algorithm
+	to use.  Pass in a 160-bit hint if any of the signing keys are
+	DSA.
+
+	* keydb.h, pkclist.c (select_algo_from_prefs, algo_available):
+	Pass a "hints" opaque pointer in to let the caller give hints as
+	to what algorithms would be acceptable.  The only current hint is
+	for PREFTYPE_HASH to require a 160-bit hash for DSA.  Change all
+	callers in encode.c (encode_crypt, encrypt_filter) and sign.c
+	(sign_file).  If we settle on MD5 as the best algorithm based
+	solely on recepient keys and SHA1 is also a possibility, use SHA1
+	unless the user intentionally chose MD5.  This is as per 2440:13.
+
+	* exec.c (make_tempdir): Fix duplicated filename problem.
+
 2002-06-03  David Shaw  <[email protected]>
 
 	* packet.h, parse-packet.c (enum_sig_subpkt): Report back from
diff --git a/g10/encode.c b/g10/encode.c
index 8033201d4..141e4363f 100644
--- a/g10/encode.c
+++ b/g10/encode.c
@@ -336,7 +336,7 @@ encode_crypt( const char *filename, STRLIST remusr )
     /* create a session key */
     cfx.dek = m_alloc_secure_clear (sizeof *cfx.dek);
     if( !opt.def_cipher_algo ) { /* try to get it from the prefs */
-	cfx.dek->algo = select_algo_from_prefs( pk_list, PREFTYPE_SYM );
+	cfx.dek->algo = select_algo_from_prefs( pk_list, PREFTYPE_SYM, NULL );
 	/* The only way select_algo_from_prefs can fail here is when
            mixing v3 and v4 keys, as v4 keys have an implicit
            preference entry for 3DES, and the pk_list cannot be empty.
@@ -415,7 +415,8 @@ encode_crypt( const char *filename, STRLIST remusr )
 
 	if(compr_algo==-1)
 	  {
-	    if((compr_algo=select_algo_from_prefs( pk_list, PREFTYPE_ZIP))==-1)
+	    if((compr_algo=
+		select_algo_from_prefs(pk_list,PREFTYPE_ZIP,NULL))==-1)
 	      compr_algo=DEFAULT_COMPRESS_ALGO;
 	  }
 
@@ -485,7 +486,7 @@ encrypt_filter( void *opaque, int control,
 
 	    if( !opt.def_cipher_algo  ) { /* try to get it from the prefs */
 		efx->cfx.dek->algo =
-			  select_algo_from_prefs( efx->pk_list, PREFTYPE_SYM );
+		  select_algo_from_prefs( efx->pk_list, PREFTYPE_SYM, NULL );
 		if( efx->cfx.dek->algo == -1 ) {
                     /* because 3DES is implicitly in the prefs, this can only
                      * happen if we do not have any public keys in the list */
diff --git a/g10/exec.c b/g10/exec.c
index 8aa87dd0c..d8111bdca 100644
--- a/g10/exec.c
+++ b/g10/exec.c
@@ -93,10 +93,12 @@ static int win_system(const char *command)
 /* Makes a temp directory and filenames */
 static int make_tempdir(struct exec_info *info)
 {
-  char *tmp=opt.temp_dir,*name=info->name;
+  char *tmp=opt.temp_dir,*namein=info->name,*nameout;
 
-  if(!name)
-    name=info->binary?"tempfile" EXTSEP_S "bin":"tempfile" EXTSEP_S "txt";
+  if(!namein)
+    namein=info->binary?"tempin" EXTSEP_S "bin":"tempin" EXTSEP_S "txt";
+
+  nameout=info->binary?"tempout" EXTSEP_S "bin":"tempout" EXTSEP_S "txt";
 
   /* Make up the temp dir and files in case we need them */
 
@@ -151,14 +153,14 @@ static int make_tempdir(struct exec_info *info)
       info->madedir=1;
 
       info->tempfile_in=m_alloc(strlen(info->tempdir)+
-				strlen(DIRSEP_S)+strlen(name)+1);
-      sprintf(info->tempfile_in,"%s" DIRSEP_S "%s",info->tempdir,name);
+				strlen(DIRSEP_S)+strlen(namein)+1);
+      sprintf(info->tempfile_in,"%s" DIRSEP_S "%s",info->tempdir,namein);
 
       if(!info->writeonly)
 	{
 	  info->tempfile_out=m_alloc(strlen(info->tempdir)+
-				     strlen(DIRSEP_S)+strlen(name)+1);
-	  sprintf(info->tempfile_out,"%s" DIRSEP_S "%s",info->tempdir,name);
+				     strlen(DIRSEP_S)+strlen(nameout)+1);
+	  sprintf(info->tempfile_out,"%s" DIRSEP_S "%s",info->tempdir,nameout);
 	}
     }
 
diff --git a/g10/keydb.h b/g10/keydb.h
index ee2f0c8af..dc7863a99 100644
--- a/g10/keydb.h
+++ b/g10/keydb.h
@@ -166,7 +166,7 @@ void show_revocation_reason( PKT_public_key *pk, int mode );
 int  check_signatures_trust( PKT_signature *sig );
 void release_pk_list( PK_LIST pk_list );
 int  build_pk_list( STRLIST remusr, PK_LIST *ret_pk_list, unsigned use );
-int  select_algo_from_prefs( PK_LIST pk_list, int preftype );
+int  select_algo_from_prefs( PK_LIST pk_list, int preftype, void *hint );
 int  select_mdc_from_pklist (PK_LIST pk_list);
 
 /*-- skclist.c --*/
diff --git a/g10/pkclist.c b/g10/pkclist.c
index 190faaec9..f3b247850 100644
--- a/g10/pkclist.c
+++ b/g10/pkclist.c
@@ -970,7 +970,7 @@ build_pk_list( STRLIST remusr, PK_LIST *ret_pk_list, unsigned use )
    such a broken preference list, so I'm including it. -dms */
 
 static int
-algo_available( int preftype, int algo )
+algo_available( int preftype, int algo, void *hint )
 {
     if( preftype == PREFTYPE_SYM ) {
         if( opt.pgp6 && ( algo != 1 && algo != 2 && algo != 3) )
@@ -983,6 +983,14 @@ algo_available( int preftype, int algo )
 	return algo && !check_cipher_algo( algo );
     }
     else if( preftype == PREFTYPE_HASH ) {
+        int bits=0;
+
+	if(hint)
+	  bits=*(int *)hint;
+
+	if(bits && (bits != md_digest_length(algo)))
+	  return 0;
+
         if( (opt.pgp6 || opt.pgp7 ) && ( algo != 1 && algo != 2 && algo != 3) )
 	  return 0;
 
@@ -1004,7 +1012,7 @@ algo_available( int preftype, int algo )
  * Return -1 if we could not find an algorithm.
  */
 int
-select_algo_from_prefs( PK_LIST pk_list, int preftype )
+select_algo_from_prefs( PK_LIST pk_list, int preftype, void *hint )
 {
     PK_LIST pkr;
     u32 bits[8];
@@ -1022,9 +1030,9 @@ select_algo_from_prefs( PK_LIST pk_list, int preftype )
 
 	memset( mask, 0, 8 * sizeof *mask );
 	if( preftype == PREFTYPE_SYM ) {
-	  if( pkr->pk->version < 4 &&
-	      pkr->pk->selfsigversion < 4 &&
-	      opt.pgp2 )
+	  if( opt.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
@@ -1033,6 +1041,21 @@ select_algo_from_prefs( PK_LIST pk_list, int preftype )
 	  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( opt.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 */
 
@@ -1086,7 +1109,7 @@ select_algo_from_prefs( PK_LIST pk_list, int preftype )
 	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 ) ) {
+		    if( algo_available( preftype, prefs[j].value, hint ) ) {
 			any = 1;
 			i = prefs[j].value;
 			break;
@@ -1098,7 +1121,7 @@ select_algo_from_prefs( PK_LIST pk_list, int preftype )
     if( !prefs || !any ) {
 	for(j=0; j < 256; j++ )
 	    if( (bits[j/32] & (1<<(j%32))) ) {
-		if( algo_available( preftype, j ) ) {
+		if( algo_available( preftype, j, hint ) ) {
 		    i = j;
 		    break;
 		}
@@ -1115,6 +1138,29 @@ select_algo_from_prefs( PK_LIST pk_list, int preftype )
 	    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 intentinally 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_prefs)
+	  for(j=0; prefs[j].type; j++ )
+	    if(opt.personal_prefs[j].type==PREFTYPE_HASH &&
+	       opt.personal_prefs[j].value==DIGEST_ALGO_MD5)
+	      {
+		i=DIGEST_ALGO_MD5;
+		break;
+	      }
+      }
+
     return i;
 }
 
@@ -1138,7 +1184,7 @@ select_mdc_from_pklist (PK_LIST pk_list)
         else
             mdc = pkr->pk->mdc_feature;
         if (!mdc)
-            return 0; /* at least on recipeint does not support it */
+            return 0; /* at least one recipient does not support it */
     }
     return 1; /* can be used */
 }
diff --git a/g10/sign.c b/g10/sign.c
index 6cf1c8804..cfab80066 100644
--- a/g10/sign.c
+++ b/g10/sign.c
@@ -49,6 +49,8 @@
   #define LF "\n"
 #endif
 
+static int recipient_digest_algo=0;
+
 /****************
  * Create a notation.  It is assumed that the stings in STRLIST
  * are already checked to contain only printable data and have a valid
@@ -332,6 +334,8 @@ hash_for(int pubkey_algo, int packet_version )
 {
     if( opt.def_digest_algo )
 	return opt.def_digest_algo;
+    if( recipient_digest_algo )
+        return recipient_digest_algo;
     if( pubkey_algo == PUBKEY_ALGO_DSA )
 	return DIGEST_ALGO_SHA1;
     if( pubkey_algo == PUBKEY_ALGO_RSA && packet_version < 4 )
@@ -673,6 +677,28 @@ sign_file( STRLIST filenames, int detached, STRLIST locusr,
 	iobuf_push_filter( inp, text_filter, &tfx );
     mfx.md = md_open(0, 0);
 
+   /* If we're encrypting and signing, it is reasonable to pick the
+       hash algorithm to use out of the recepient key prefs. */
+    if(pk_list && !opt.def_digest_algo)
+      {
+	int hashlen=0,algo;
+
+	/* Of course, if the recipient asks for something unreasonable
+	   (like a non-160-bit hash for DSA, for example), then don't
+	   do it.  Check all sk's - if any are DSA, then the hash must
+	   be 160-bit.  In the future this can be more complex with
+	   different hashes for each sk, but so long as there is only
+	   one signing algorithm with hash restrictions, this is
+	   ok. -dms */
+
+	for( sk_rover = sk_list; sk_rover; sk_rover = sk_rover->next )
+	  if(sk_rover->sk->pubkey_algo==PUBKEY_ALGO_DSA)
+	    hashlen=20;
+
+	if((algo=select_algo_from_prefs(pk_list,PREFTYPE_HASH,&hashlen))>0)
+	  recipient_digest_algo=algo;
+      }
+
     for( sk_rover = sk_list; sk_rover; sk_rover = sk_rover->next ) {
 	PKT_secret_key *sk = sk_rover->sk;
 	md_enable(mfx.md, hash_for(sk->pubkey_algo, sk->version ));
@@ -707,7 +733,8 @@ sign_file( STRLIST filenames, int detached, STRLIST locusr,
                Still, if it did fail, we'll also end up with the
                default. */
 
-	    if((compr_algo=select_algo_from_prefs( pk_list, PREFTYPE_ZIP))==-1)
+	    if((compr_algo=
+		select_algo_from_prefs(pk_list,PREFTYPE_ZIP,NULL))==-1)
 	      compr_algo=DEFAULT_COMPRESS_ALGO;
 	  }
 
@@ -788,6 +815,7 @@ sign_file( STRLIST filenames, int detached, STRLIST locusr,
     md_close( mfx.md );
     release_sk_list( sk_list );
     release_pk_list( pk_list );
+    recipient_digest_algo=0;
     return rc;
 }