Factor out hex2bin into a shared helper function. Replace sscanf %hhx

(which is C99) with plain %x for better compatibility in -portable.
ok djm@

regress/usr.bin/ssh/unittests/crypto/test_ed25519.c

@@ -1,4 +1,4 @@
-/* 	$OpenBSD: test_ed25519.c,v 1.2 2026/06/16 09:00:47 dtucker Exp $ */
+/* 	$OpenBSD: test_ed25519.c,v 1.3 2026/06/16 22:27:10 dtucker Exp $ */
 /*
  * Regress test for Ed25519 keypair from seed
  *
@@ -61,14 +61,6 @@ static const struct ed25519_kat ed25519_kats[] = {
 
 void ed25519_tests(void);
 
-static void
-hex2bin(uint8_t *bin, const char *hex, size_t len)
-{
-	size_t i;
-	for (i = 0; i < len; i++)
-		sscanf(hex + i * 2, "%02hhx", &bin[i]);
-}
-
 void
 ed25519_tests(void)
 {

regress/usr.bin/ssh/unittests/crypto/test_mldsa.c

@@ -1,4 +1,4 @@
-/* 	$OpenBSD: test_mldsa.c,v 1.2 2026/06/16 09:00:47 dtucker Exp $ */
+/* 	$OpenBSD: test_mldsa.c,v 1.3 2026/06/16 22:27:10 dtucker Exp $ */
 /*
  * Regress test for ML-DSA
  *
@@ -79,14 +79,6 @@ free_kats(struct kat **kats, size_t nkats)
 	free(kats);
 }
 
-static void
-hex2bin(uint8_t *bin, const char *hex, size_t len)
-{
-	size_t i;
-	for (i = 0; i < len; i++)
-		sscanf(hex + i * 2, "%02hhx", &bin[i]);
-}
-
 void
 mldsa_tests(void)
 {

regress/usr.bin/ssh/unittests/crypto/test_mlkem.c

@@ -1,4 +1,4 @@
-/* 	$OpenBSD: test_mlkem.c,v 1.1 2026/06/14 04:08:06 djm Exp $ */
+/* 	$OpenBSD: test_mlkem.c,v 1.2 2026/06/16 22:27:10 dtucker Exp $ */
 /*
  * Regress test for ML-KEM
  *
@@ -108,14 +108,6 @@ static const struct mlkem768_kat mlkem768_kats[] = {
 
 void mlkem_tests(void);
 
-static void
-hex2bin(uint8_t *bin, const char *hex, size_t len)
-{
-	size_t i;
-	for (i = 0; i < len; i++)
-		sscanf(hex + i * 2, "%02hhx", &bin[i]);
-}
-
 void
 mlkem_tests(void)
 {

regress/usr.bin/ssh/unittests/test_helper/test_helper.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: test_helper.c,v 1.16 2026/03/06 06:57:33 dtucker Exp $	*/
+/*	$OpenBSD: test_helper.c,v 1.17 2026/06/16 22:27:10 dtucker Exp $	*/
 /*
  * Copyright (c) 2011 Damien Miller <djm@mindrot.org>
  *
@@ -626,6 +626,20 @@ tstod(const struct timespec *ts)
 	return (double)ts->tv_sec + ((double)ts->tv_nsec / 1000000000.0);
 }
 
+void
+hex2bin(uint8_t *bin, const char *hex, size_t len)
+{
+	size_t i;
+	unsigned int v;
+
+	/* Don't use %hhx since it's C99 and older platforms don't have it. */
+	for (i = 0; i < len; i++) {
+		sscanf(hex + i * 2, "%02x", &v);
+		ASSERT_U_INT_LE(v, 256);
+		bin[i] = (uint8_t)v;
+	}
+}
+
 void
 bench_start(const char *file, int line, const char *name)
 {

regress/usr.bin/ssh/unittests/test_helper/test_helper.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: test_helper.h,v 1.12 2026/03/06 06:57:33 dtucker Exp $	*/
+/*	$OpenBSD: test_helper.h,v 1.13 2026/06/16 22:27:10 dtucker Exp $	*/
 /*
  * Copyright (c) 2011 Damien Miller <djm@mindrot.org>
  *
@@ -35,6 +35,8 @@ typedef void (test_onerror_func_t)(void *);
 void tests(void);
 void benchmarks(void);
 
+void hex2bin(uint8_t *, const char *, size_t);
+
 const char *test_data_file(const char *name);
 void test_start(const char *n);
 void test_info(char *s, size_t len);