New "i62" code for big integers with 64x64->128 opcodes; also improved "i31" modular...

[BearSSL] / src / rsa / rsa_i62_pub.c

diff --git a/src/rsa/rsa_i62_pub.c b/src/rsa/rsa_i62_pub.c
new file mode 100644 (file)
index 0000000..70cf61b
--- /dev/null
+++ b/src/rsa/rsa_i62_pub.c
@@ -0,0 +1,125 @@
+/*
+ * Copyright (c) 2016 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"
+
+#if BR_INT128 || BR_UMUL128
+
+/*
+ * As a strict minimum, we need four buffers that can hold a
+ * modular integer. But TLEN is expressed in 64-bit words.
+ */
+#define TLEN   (2 * (2 + ((BR_MAX_RSA_SIZE + 30) / 31)))
+
+/* see bearssl_rsa.h */
+uint32_t
+br_rsa_i62_public(unsigned char *x, size_t xlen,
+       const br_rsa_public_key *pk)
+{
+       const unsigned char *n;
+       size_t nlen;
+       uint64_t tmp[TLEN];
+       uint32_t *m, *a;
+       size_t fwlen;
+       long z;
+       uint32_t m0i, r;
+
+       /*
+        * Get the actual length of the modulus, and see if it fits within
+        * our stack buffer. We also check that the length of x[] is valid.
+        */
+       n = pk->n;
+       nlen = pk->nlen;
+       while (nlen > 0 && *n == 0) {
+               n ++;
+               nlen --;
+       }
+       if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) {
+               return 0;
+       }
+       z = (long)nlen << 3;
+       fwlen = 1;
+       while (z > 0) {
+               z -= 31;
+               fwlen ++;
+       }
+       /*
+        * Convert fwlen to a count in 62-bit words.
+        */
+       fwlen = (fwlen + 1) >> 1;
+
+       /*
+        * The modulus gets decoded into m[].
+        * The value to exponentiate goes into a[].
+        */
+       m = (uint32_t *)tmp;
+       a = (uint32_t *)(tmp + fwlen);
+
+       /*
+        * Decode the modulus.
+        */
+       br_i31_decode(m, n, nlen);
+       m0i = br_i31_ninv31(m[1]);
+
+       /*
+        * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be
+        * an odd integer.
+        */
+       r = m0i & 1;
+
+       /*
+        * Decode x[] into a[]; we also check that its value is proper.
+        */
+       r &= br_i31_decode_mod(a, x, xlen, m);
+
+       /*
+        * Compute the modular exponentiation.
+        */
+       br_i62_modpow_opt(a, pk->e, pk->elen, m, m0i,
+               tmp + 2 * fwlen, TLEN - 2 * fwlen);
+
+       /*
+        * Encode the result.
+        */
+       br_i31_encode(x, xlen, a);
+       return r;
+}
+
+/* see bearssl_rsa.h */
+br_rsa_public
+br_rsa_i62_public_get(void)
+{
+       return &br_rsa_i62_public;
+}
+
+#else
+
+/* see bearssl_rsa.h */
+br_rsa_public
+br_rsa_i62_public_get(void)
+{
+       return 0;
+}
+
+#endif