New "i15" implementation of big integers (faster, and constant-time, on ARM Cortex...

[BearSSL] / src / rsa / rsa_pkcs1_sig_pad.c

diff --git a/src/rsa/rsa_pkcs1_sig_pad.c b/src/rsa/rsa_pkcs1_sig_pad.c
new file mode 100644 (file)
index 0000000..06c3bd7
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+++ b/src/rsa/rsa_pkcs1_sig_pad.c
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+/*
+ * 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"
+
+/* see inner.h */
+uint32_t
+br_rsa_pkcs1_sig_pad(const unsigned char *hash_oid,
+       const unsigned char *hash, size_t hash_len,
+       uint32_t n_bitlen, unsigned char *x)
+{
+       size_t u, x3, xlen;
+
+       /*
+        * Padded hash value has format:
+        *  00 01 FF .. FF 00 30 x1 30 x2 06 x3 OID 05 00 04 x4 HASH
+        *
+        * with the following rules:
+        *
+        *  -- Total length is equal to the modulus length (unsigned
+        *     encoding).
+        *
+        *  -- There must be at least eight bytes of value 0xFF.
+        *
+        *  -- x4 is equal to the hash length (hash_len).
+        *
+        *  -- x3 is equal to the encoded OID value length (hash_oid[0]).
+        *
+        *  -- x2 = x3 + 4.
+        *
+        *  -- x1 = x2 + x4 + 4 = x3 + x4 + 8.
+        *
+        * Note: the "05 00" is optional (signatures with and without
+        * that sequence exist in practice), but notes in PKCS#1 seem to
+        * indicate that the presence of that sequence (specifically,
+        * an ASN.1 NULL value for the hash parameters) may be slightly
+        * more "standard" than the opposite.
+        */
+       xlen = (n_bitlen + 7) >> 3;
+
+       if (hash_oid == NULL) {
+               if (xlen < hash_len + 11) {
+                       return 0;
+               }
+               x[0] = 0x00;
+               x[1] = 0x01;
+               u = xlen - hash_len;
+               memset(x + 2, 0xFF, u - 3);
+               x[u - 1] = 0x00;
+       } else {
+               x3 = hash_oid[0];
+
+               /*
+                * Check that there is enough room for all the elements,
+                * including at least eight bytes of value 0xFF.
+                */
+               if (xlen < (x3 + hash_len + 21)) {
+                       return 0;
+               }
+               x[0] = 0x00;
+               x[1] = 0x01;
+               u = xlen - x3 - hash_len - 11;
+               memset(x + 2, 0xFF, u - 2);
+               x[u] = 0x00;
+               x[u + 1] = 0x30;
+               x[u + 2] = x3 + hash_len + 8;
+               x[u + 3] = 0x30;
+               x[u + 4] = x3 + 4;
+               x[u + 5] = 0x06;
+               memcpy(x + u + 6, hash_oid, x3 + 1);
+               u += x3 + 7;
+               x[u ++] = 0x05;
+               x[u ++] = 0x00;
+               x[u ++] = 0x04;
+               x[u ++] = hash_len;
+       }
+       memcpy(x + u, hash, hash_len);
+       return 1;
+}