X-Git-Url: https://bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=src%2Frsa%2Frsa_pss_sig_unpad.c;fp=src%2Frsa%2Frsa_pss_sig_unpad.c;h=a9f8ca3ac10f6c6d467b98dbae1de79eff97801c;hp=0000000000000000000000000000000000000000;hb=420f50c213231244c8659d2e35cecb396a250ecc;hpb=966078b3373a273f8417ede42ecab32a414dc109

diff --git a/src/rsa/rsa_pss_sig_unpad.c b/src/rsa/rsa_pss_sig_unpad.c
new file mode 100644
index 0000000..a9f8ca3
--- /dev/null
+++ b/src/rsa/rsa_pss_sig_unpad.c
@@ -0,0 +1,121 @@
+/*
+ * Copyright (c) 2018 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"
+
+/* see inner.h */
+uint32_t
+br_rsa_pss_sig_unpad(const br_hash_class *hf_data,
+	const br_hash_class *hf_mgf1,
+	const unsigned char *hash, size_t salt_len,
+	const br_rsa_public_key *pk, unsigned char *x)
+{
+	size_t u, xlen, hash_len;
+	br_hash_compat_context hc;
+	unsigned char *seed, *salt;
+	unsigned char tmp[64];
+	uint32_t r, n_bitlen;
+
+	hash_len = br_digest_size(hf_data);
+
+	/*
+	 * Value r will be set to a non-zero value is any test fails.
+	 */
+	r = 0;
+
+	/*
+	 * The value bit length (as an integer) must be strictly less than
+	 * that of the modulus.
+	 */
+	for (u = 0; u < pk->nlen; u ++) {
+		if (pk->n[u] != 0) {
+			break;
+		}
+	}
+	if (u == pk->nlen) {
+		return 0;
+	}
+	n_bitlen = BIT_LENGTH(pk->n[u]) + ((uint32_t)(pk->nlen - u - 1) << 3);
+	n_bitlen --;
+	if ((n_bitlen & 7) == 0) {
+		r |= *x ++;
+	} else {
+		r |= x[0] & (0xFF << (n_bitlen & 7));
+	}
+	xlen = (n_bitlen + 7) >> 3;
+
+	/*
+	 * Check that the modulus is large enough for the hash value
+	 * length combined with the intended salt length.
+	 */
+	if (hash_len > xlen || salt_len > xlen
+		|| (hash_len + salt_len + 2) > xlen)
+	{
+		return 0;
+	}
+
+	/*
+	 * Check value of rightmost byte.
+	 */
+	r |= x[xlen - 1] ^ 0xBC;
+
+	/*
+	 * Generate the mask and XOR it into the first bytes to reveal PS;
+	 * we must also mask out the leading bits.
+	 */
+	seed = x + xlen - hash_len - 1;
+	br_mgf1_xor(x, xlen - hash_len - 1, hf_mgf1, seed, hash_len);
+	if ((n_bitlen & 7) != 0) {
+		x[0] &= 0xFF >> (8 - (n_bitlen & 7));
+	}
+
+	/*
+	 * Check that all padding bytes have the expected value.
+	 */
+	for (u = 0; u < (xlen - hash_len - salt_len - 2); u ++) {
+		r |= x[u];
+	}
+	r |= x[xlen - hash_len - salt_len - 2] ^ 0x01;
+
+	/*
+	 * Recompute H.
+	 */
+	salt = x + xlen - hash_len - salt_len - 1;
+	hf_data->init(&hc.vtable);
+	memset(tmp, 0, 8);
+	hf_data->update(&hc.vtable, tmp, 8);
+	hf_data->update(&hc.vtable, hash, hash_len);
+	hf_data->update(&hc.vtable, salt, salt_len);
+	hf_data->out(&hc.vtable, tmp);
+
+	/*
+	 * Check that the recomputed H value matches the one appearing
+	 * in the string.
+	 */
+	for (u = 0; u < hash_len; u ++) {
+		r |= tmp[u] ^ x[(xlen - salt_len - 1) + u];
+	}
+
+	return EQ0(r);
+}