Added support code for RSA and EC key encoding (including reconstruction of all publi...

[BearSSL] / src / rsa / rsa_i15_modulus.c

diff --git a/src/rsa/rsa_i15_modulus.c b/src/rsa/rsa_i15_modulus.c
new file mode 100644 (file)
index 0000000..d61c794
--- /dev/null
+++ b/src/rsa/rsa_i15_modulus.c
@@ -0,0 +1,99 @@
+/*
+ * 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 bearssl_rsa.h */
+size_t
+br_rsa_i15_compute_modulus(void *n, const br_rsa_private_key *sk)
+{
+       uint16_t tmp[2 * ((BR_MAX_RSA_SIZE + 14) / 15) + 5];
+       uint16_t *t, *p, *q;
+       const unsigned char *pbuf, *qbuf;
+       size_t nlen, plen, qlen, tlen;
+
+       /*
+        * Compute actual byte and lengths for p and q.
+        */
+       pbuf = sk->p;
+       plen = sk->plen;
+       while (plen > 0 && *pbuf == 0) {
+               pbuf ++;
+               plen --;
+       }
+       qbuf = sk->q;
+       qlen = sk->qlen;
+       while (qlen > 0 && *qbuf == 0) {
+               qbuf ++;
+               qlen --;
+       }
+
+       t = tmp;
+       tlen = (sizeof tmp) / (sizeof tmp[0]);
+
+       /*
+        * Decode p.
+        */
+       if ((15 * tlen) < (plen << 3) + 15) {
+               return 0;
+       }
+       br_i15_decode(t, pbuf, plen);
+       p = t;
+       plen = (p[0] + 31) >> 4;
+       t += plen;
+       tlen -= plen;
+
+       /*
+        * Decode q.
+        */
+       if ((15 * tlen) < (qlen << 3) + 15) {
+               return 0;
+       }
+       br_i15_decode(t, qbuf, qlen);
+       q = t;
+       qlen = (q[0] + 31) >> 4;
+       t += qlen;
+       tlen -= qlen;
+
+       /*
+        * Computation can proceed only if we have enough room for the
+        * modulus.
+        */
+       if (tlen < (plen + qlen + 1)) {
+               return 0;
+       }
+
+       /*
+        * Private key already contains the modulus bit length, from which
+        * we can infer the output length. Even if n is NULL, we still had
+        * to decode p and q to make sure that the product can be computed.
+        */
+       nlen = (sk->n_bitlen + 7) >> 3;
+       if (n != NULL) {
+               br_i15_zero(t, p[0]);
+               br_i15_mulacc(t, p, q);
+               br_i15_encode(n, nlen, t);
+       }
+       return nlen;
+}