shift overflow in mpi/mpicoder.c

[TOGAWA Satoshi]

Hello.

I'm try to run RSA key-generate code in H8/300H processer (16bit CPU).
I used GnuPG-1.0.7's code, and I found shift overflow in mpi/mpicoder.c
when BYTES_PER_MPI_LIMB == 4.


--- mpicoder.c.orig	Tue Sep  3 09:18:44 2002
+++ mpicoder.c	Tue Sep  3 09:21:44 2002
@@ -402,10 +402,10 @@
 
     for(i=0, p = buffer+nbytes-1; p >= buffer+BYTES_PER_MPI_LIMB; ) {
       #if BYTES_PER_MPI_LIMB == 4
-	alimb  = *p--	    ;
-	alimb |= *p-- <<  8 ;
-	alimb |= *p-- << 16 ;
-	alimb |= *p-- << 24 ;
+	alimb  = (mpi_limb_t)*p--	    ;
+	alimb |= (mpi_limb_t)*p-- <<  8 ;
+	alimb |= (mpi_limb_t)*p-- << 16 ;
+	alimb |= (mpi_limb_t)*p-- << 24 ;
       #elif BYTES_PER_MPI_LIMB == 8
 	alimb  = (mpi_limb_t)*p--	;
 	alimb |= (mpi_limb_t)*p-- <<  8 ;
@@ -422,10 +422,10 @@
     }
     if( p >= buffer ) {
       #if BYTES_PER_MPI_LIMB == 4
-	alimb  = *p--	    ;
-	if( p >= buffer ) alimb |= *p-- <<  8 ;
-	if( p >= buffer ) alimb |= *p-- << 16 ;
-	if( p >= buffer ) alimb |= *p-- << 24 ;
+	alimb  = (mpi_limb_t)*p--	    ;
+	if( p >= buffer ) alimb |= (mpi_limb_t)*p-- <<  8 ;
+	if( p >= buffer ) alimb |= (mpi_limb_t)*p-- << 16 ;
+	if( p >= buffer ) alimb |= (mpi_limb_t)*p-- << 24 ;
       #elif BYTES_PER_MPI_LIMB == 8
 	alimb  = (mpi_limb_t)*p-- ;
 	if( p >= buffer ) alimb |= (mpi_limb_t)*p-- <<	8 ;


In this function, *p is byte type. So when we do (*p<<16) in CPU
whose integer is 16bit, shift overflow occered.


Regards,


Satoshi.Togawa at jp.yokogawa.com