Added stand-alone RSA/PSS implementation.

[BearSSL] / src / rsa / rsa_pss_sig_pad.c

diff --git a/src/rsa/rsa_pss_sig_pad.c b/src/rsa/rsa_pss_sig_pad.c
new file mode 100644 (file)
index 0000000..13e9027
--- /dev/null
+++ 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;
+}