X-Git-Url: https://bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=src%2Frsa%2Frsa_pss_sig_pad.c;fp=src%2Frsa%2Frsa_pss_sig_pad.c;h=13e902745ec90a31f0665e326d22f12cdbfc272a;hp=0000000000000000000000000000000000000000;hb=420f50c213231244c8659d2e35cecb396a250ecc;hpb=966078b3373a273f8417ede42ecab32a414dc109

diff --git a/src/rsa/rsa_pss_sig_pad.c b/src/rsa/rsa_pss_sig_pad.c
new file mode 100644
index 0000000..13e9027
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+++ b/src/rsa/rsa_pss_sig_pad.c
@@ -0,0 +1,106 @@
+/*
+ * 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_pad(const br_prng_class **rng,
+	const br_hash_class *hf_data, const br_hash_class *hf_mgf1,
+	const unsigned char *hash, size_t salt_len,
+	uint32_t n_bitlen, unsigned char *x)
+{
+	size_t xlen, hash_len;
+	br_hash_compat_context hc;
+	unsigned char *salt, *seed;
+
+	hash_len = br_digest_size(hf_data);
+
+	/*
+	 * The padded string is one bit smaller than the modulus;
+	 * notably, if the modulus length is equal to 1 modulo 8, then
+	 * the padded string will be one _byte_ smaller, and the first
+	 * byte will be set to 0. We apply these transformations here.
+	 */
+	n_bitlen --;
+	if ((n_bitlen & 7) == 0) {
+		*x ++ = 0;
+	}
+	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;
+	}
+
+	/*
+	 * Produce a random salt.
+	 */
+	salt = x + xlen - hash_len - salt_len - 1;
+	if (salt_len != 0) {
+		(*rng)->generate(rng, salt, salt_len);
+	}
+
+	/*
+	 * Compute the seed for MGF1.
+	 */
+	seed = x + xlen - hash_len - 1;
+	hf_data->init(&hc.vtable);
+	memset(seed, 0, 8);
+	hf_data->update(&hc.vtable, seed, 8);
+	hf_data->update(&hc.vtable, hash, hash_len);
+	hf_data->update(&hc.vtable, salt, salt_len);
+	hf_data->out(&hc.vtable, seed);
+
+	/*
+	 * Prepare string PS (padded salt). The salt is already at the
+	 * right place.
+	 */
+	memset(x, 0, xlen - salt_len - hash_len - 2);
+	x[xlen - salt_len - hash_len - 2] = 0x01;
+
+	/*
+	 * Generate the mask and XOR it into PS.
+	 */
+	br_mgf1_xor(x, xlen - hash_len - 1, hf_mgf1, seed, hash_len);
+
+	/*
+	 * Clear the top bits to ensure the value is lower than the
+	 * modulus.
+	 */
+	x[0] &= 0xFF >> (((uint32_t)xlen << 3) - n_bitlen);
+
+	/*
+	 * The seed (H) is already in the right place. We just set the
+	 * last byte.
+	 */
+	x[xlen - 1] = 0xBC;
+
+	return 1;
+}