Fixed a serious bug in the MPI lib

[Werner Koch]

Thomas Roessler <roessler at guug.de> writes:

> I'm afraid things aren't so easy.  The key in question _does_ have a
> certified user id, but gpg says that this self signature is invalid.

This bug caused bad verification of signatures because the compare
function assumed normalized values - this was not always true and is
now fixed. 

I'll put it into the CVS but some things are still not working
(cleartext).  

Ralf and Stefan: Are your problems now solved? I'm quite sure about
Ralfs' as I used this as a test case.


  Werner


p.s. And here is the mpi patch (yes: the prototype is missing)

Index: mpi/mpi-bit.c
===================================================================
RCS file: /home/koch/cvs/gnupg/mpi/mpi-bit.c,v
retrieving revision 1.13
retrieving revision 1.14
diff -u -r1.13 -r1.14
--- mpi-bit.c	1998/12/23 12:41:29	1.13
+++ mpi-bit.c	1999/01/07 17:05:44	1.14
@@ -48,7 +48,19 @@
 #define A_LIMB_1 ((mpi_limb_t)1)
 
 
+/****************
+ * Sometimes we have MSL (most significant limbs) which are 0;
+ * this is for some reasons not good, so this function removes them.
+ */
+void
+mpi_normalize( MPI a )
+{
+    if( mpi_is_protected(a) )
+	return;
 
+    for( ; a->nlimbs && !a->d[a->nlimbs-1]; a->nlimbs-- )
+	;
+}
 
 
 
@@ -67,6 +79,7 @@
 	return n;
     }
 
+    mpi_normalize( a );
     if( a->nlimbs ) {
 	mpi_limb_t alimb = a->d[a->nlimbs-1];
 	if( alimb )
Index: mpi/mpi-cmp.c
===================================================================
RCS file: /home/koch/cvs/gnupg/mpi/mpi-cmp.c,v
retrieving revision 1.3
retrieving revision 1.4
diff -u -r1.3 -r1.4
--- mpi-cmp.c	1998/12/23 12:41:29	1.3
+++ mpi-cmp.c	1999/01/07 17:05:44	1.4
@@ -46,27 +46,28 @@
 int
 mpi_cmp( MPI u, MPI v )
 {
-    mpi_size_t usize = u->nlimbs;
-    mpi_size_t vsize = v->nlimbs;
+    mpi_size_t usize, vsize;
     int cmp;
 
-    /* FIXME: are the numbers always normalized? */
+    mpi_normalize( u );
+    mpi_normalize( v );
+    usize = u->nlimbs;
+    vsize = v->nlimbs;
     if( !u->sign && v->sign )
 	return 1;
-    else if( u->sign && !v->sign )
+    if( u->sign && !v->sign )
 	return -1;
-    else if( usize != vsize && !u->sign && !v->sign )
+    if( usize != vsize && !u->sign && !v->sign )
 	return usize - vsize;
-    else if( usize != vsize && u->sign && v->sign )
+    if( usize != vsize && u->sign && v->sign )
 	return vsize + usize;
-    else if( !usize )
+    if( !usize )
 	return 0;
-    else if( !(cmp=mpihelp_cmp( u->d, v->d, usize )) )
+    if( !(cmp=mpihelp_cmp( u->d, v->d, usize )) )
 	return 0;
-    else if( (cmp < 0?1:0) == (u->sign?1:0))
+    if( (cmp < 0?1:0) == (u->sign?1:0))
 	return 1;
-    else
-	return -1;
+    return -1;
 }