Simplify tls1_set_ec_id() a bit

Use more descriptive variable names, explain why NID_undef is fine
and simplify the logic.

ok beck jsing

1 files changed, 19 insertions, 24 deletions

diff --git a/lib/libssl/t1_lib.c b/lib/libssl/t1_lib.c
index 2bc830b2ed5..f091dd001be 100644
--- a/lib/libssl/t1_lib.c
+++ b/lib/libssl/t1_lib.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: t1_lib.c,v 1.175 2020/09/07 08:04:29 tb Exp $ */
+/* $OpenBSD: t1_lib.c,v 1.176 2020/09/12 17:25:11 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -506,43 +506,38 @@ tls1_set_ec_id(uint16_t *curve_id, uint8_t *comp_id, EC_KEY *ec)
 {
 	const EC_GROUP *grp;
 	const EC_METHOD *meth;
-	int is_prime = 0;
-	int nid, id;
+	int prime_field;
+	int nid;
 
 	if (ec == NULL)
 		return (0);
 
-	/* Determine if it is a prime field. */
+	/* Determine whether the curve is defined over a prime field. */
 	if ((grp = EC_KEY_get0_group(ec)) == NULL)
 		return (0);
 	if ((meth = EC_GROUP_method_of(grp)) == NULL)
 		return (0);
-	if (EC_METHOD_get_field_type(meth) == NID_X9_62_prime_field)
-		is_prime = 1;
+	prime_field = (EC_METHOD_get_field_type(meth) == NID_X9_62_prime_field);
 
-	/* Determine curve ID. */
+	/* Determine curve ID - NID_undef results in a curve ID of zero. */
 	nid = EC_GROUP_get_curve_name(grp);
-	id = tls1_ec_nid2curve_id(nid);
-
 	/* If we have an ID set it, otherwise set arbitrary explicit curve. */
-	if (id != 0)
-		*curve_id = id;
-	else
-		*curve_id = is_prime ? 0xff01 : 0xff02;
+	if ((*curve_id = tls1_ec_nid2curve_id(nid)) == 0)
+		*curve_id = prime_field ? 0xff01 : 0xff02;
 
-	/* Specify the compression identifier. */
-	if (comp_id != NULL) {
-		if (EC_KEY_get0_public_key(ec) == NULL)
-			return (0);
+	if (comp_id == NULL)
+		return (1);
 
-		if (EC_KEY_get_conv_form(ec) == POINT_CONVERSION_COMPRESSED) {
-			*comp_id = is_prime ?
-			    TLSEXT_ECPOINTFORMAT_ansiX962_compressed_prime :
-			    TLSEXT_ECPOINTFORMAT_ansiX962_compressed_char2;
-		} else {
-			*comp_id = TLSEXT_ECPOINTFORMAT_uncompressed;
-		}
+	/* Specify the compression identifier. */
+	if (EC_KEY_get0_public_key(ec) == NULL)
+		return (0);
+	*comp_id = TLSEXT_ECPOINTFORMAT_uncompressed;
+	if (EC_KEY_get_conv_form(ec) == POINT_CONVERSION_COMPRESSED) {
+		*comp_id = TLSEXT_ECPOINTFORMAT_ansiX962_compressed_char2;
+		if (prime_field)
+			*comp_id = TLSEXT_ECPOINTFORMAT_ansiX962_compressed_prime;
 	}
+
 	return (1);
 }