Added stand-alone RSA/PSS implementation.

[BearSSL] / src / rsa / rsa_pss_sig_unpad.c

diff --git a/src/rsa/rsa_pss_sig_unpad.c b/src/rsa/rsa_pss_sig_unpad.c
new file mode 100644 (file)
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);
+}