New "i15" implementation of big integers (faster, and constant-time, on ARM Cortex M0/M0+); imported into EC, ECDSA, RSA.

src/ec/ecdsa_i15_vrfy_asn1.c

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining 
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be 
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "inner.h"
+
+#define FIELD_LEN   ((BR_MAX_EC_SIZE + 7) >> 3)
+
+/* see bearssl_ec.h */
+uint32_t
+br_ecdsa_i15_vrfy_asn1(const br_ec_impl *impl,
+	const void *hash, size_t hash_len,
+	const br_ec_public_key *pk,
+	const void *sig, size_t sig_len)
+{
+	/*
+	 * We use a double-sized buffer because a malformed ASN.1 signature
+	 * may trigger a size expansion when converting to "raw" format.
+	 */
+	unsigned char rsig[(FIELD_LEN << 2) + 24];
+
+	if (sig_len > ((sizeof rsig) >> 1)) {
+		return 0;
+	}
+	memcpy(rsig, sig, sig_len);
+	sig_len = br_ecdsa_asn1_to_raw(rsig, sig_len);
+	return br_ecdsa_i15_vrfy_raw(impl, hash, hash_len, pk, rsig, sig_len);
+}