X-Git-Url: https://www.bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=src%2Fec%2Fec_c25519_i31.c;h=f8ffc2c243af925b4cb394cd286f9f37af96218c;hp=d030c50278b6de7aefb5c5b3629b738f6f71df22;hb=4b6046412bf927d6424f20fc7ee495bb96dbd227;hpb=fd98320c82b02ded99cc8f01a7510366def3bbeb;ds=sidebyside

diff --git a/src/ec/ec_c25519_i31.c b/src/ec/ec_c25519_i31.c
index d030c50..f8ffc2c 100644
--- a/src/ec/ec_c25519_i31.c
+++ b/src/ec/ec_c25519_i31.c
@@ -230,11 +230,14 @@ api_mul(unsigned char *G, size_t Glen,
 	x2[1] = 0x13000000;
 	memcpy(z3, x2, sizeof x2);
 
-	memcpy(k, kb, kblen);
-	memset(k + kblen, 0, (sizeof k) - kblen);
-	k[0] &= 0xF8;
-	k[31] &= 0x7F;
-	k[31] |= 0x40;
+	/*
+	 * kb[] is in big-endian notation, but possibly shorter than k[].
+	 */
+	memset(k, 0, (sizeof k) - kblen);
+	memcpy(k + (sizeof k) - kblen, kb, kblen);
+	k[31] &= 0xF8;
+	k[0] &= 0x7F;
+	k[0] |= 0x40;
 
 	/* obsolete
 	print_int_mont("x1", x1);
@@ -244,7 +247,7 @@ api_mul(unsigned char *G, size_t Glen,
 	for (i = 254; i >= 0; i --) {
 		uint32_t kt;
 
-		kt = (k[i >> 3] >> (i & 7)) & 1;
+		kt = (k[31 - (i >> 3)] >> (i & 7)) & 1;
 		swap ^= kt;
 		cswap(x2, x3, swap);
 		cswap(z2, z3, swap);