X-Git-Url: https://bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=src%2Frsa%2Frsa_i62_priv.c;fp=src%2Frsa%2Frsa_i62_priv.c;h=ffa03c27a544ae6cf98d7f86a70a26c5e334ac35;hp=0000000000000000000000000000000000000000;hb=8b2fe3add686db5cbd977e75d3bef02fa4c98c8f;hpb=90bc9406c31e03d09b3d835c3cbabfec83f4e94d

diff --git a/src/rsa/rsa_i62_priv.c b/src/rsa/rsa_i62_priv.c
new file mode 100644
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+++ b/src/rsa/rsa_i62_priv.c
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+/*
+ * 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
+
+#define U      (2 + ((BR_MAX_RSA_FACTOR + 30) / 31))
+#define TLEN   (4 * U)  /* TLEN is counted in 64-bit words */
+
+/* see bearssl_rsa.h */
+uint32_t
+br_rsa_i62_private(unsigned char *x, const br_rsa_private_key *sk)
+{
+	const unsigned char *p, *q;
+	size_t plen, qlen;
+	size_t fwlen;
+	uint32_t p0i, q0i;
+	size_t xlen;
+	uint64_t tmp[TLEN];
+	long z;
+	uint32_t *mp, *mq, *s1, *s2, *t1, *t2, *t3;
+	uint32_t r;
+
+	/*
+	 * Compute the actual lengths of p and q, in bytes.
+	 * These lengths are not considered secret (we cannot really hide
+	 * them anyway in constant-time code).
+	 */
+	p = sk->p;
+	plen = sk->plen;
+	while (plen > 0 && *p == 0) {
+		p ++;
+		plen --;
+	}
+	q = sk->q;
+	qlen = sk->qlen;
+	while (qlen > 0 && *q == 0) {
+		q ++;
+		qlen --;
+	}
+
+	/*
+	 * Compute the maximum factor length, in words.
+	 */
+	z = (long)(plen > qlen ? plen : qlen) << 3;
+	fwlen = 1;
+	while (z > 0) {
+		z -= 31;
+		fwlen ++;
+	}
+
+	/*
+	 * Convert size to 62-bit words.
+	 */
+	fwlen = (fwlen + 1) >> 1;
+
+	/*
+	 * We need to fit at least 6 values in the stack buffer.
+	 */
+	if (6 * fwlen > TLEN) {
+		return 0;
+	}
+
+	/*
+	 * Compute signature length (in bytes).
+	 */
+	xlen = (sk->n_bitlen + 7) >> 3;
+
+	/*
+	 * Decode q.
+	 */
+	mq = (uint32_t *)tmp;
+	br_i31_decode(mq, q, qlen);
+
+	/*
+	 * Compute s2 = x^dq mod q.
+	 */
+	q0i = br_i31_ninv31(mq[1]);
+	s2 = (uint32_t *)(tmp + fwlen);
+	br_i31_decode_reduce(s2, x, xlen, mq);
+	r = br_i62_modpow_opt(s2, sk->dq, sk->dqlen, mq, q0i,
+		tmp + 2 * fwlen, TLEN - 2 * fwlen);
+
+	/*
+	 * Decode p.
+	 */
+	mp = (uint32_t *)(tmp + 2 * fwlen);
+	br_i31_decode(mp, p, plen);
+
+	/*
+	 * Compute s1 = x^dp mod p.
+	 */
+	p0i = br_i31_ninv31(mp[1]);
+	s1 = (uint32_t *)(tmp + 3 * fwlen);
+	br_i31_decode_reduce(s1, x, xlen, mp);
+	r &= br_i62_modpow_opt(s1, sk->dp, sk->dplen, mp, p0i,
+		tmp + 4 * fwlen, TLEN - 4 * fwlen);
+
+	/*
+	 * Compute:
+	 *   h = (s1 - s2)*(1/q) mod p
+	 * s1 is an integer modulo p, but s2 is modulo q. PKCS#1 is
+	 * unclear about whether p may be lower than q (some existing,
+	 * widely deployed implementations of RSA don't tolerate p < q),
+	 * but we want to support that occurrence, so we need to use the
+	 * reduction function.
+	 *
+	 * Since we use br_i31_decode_reduce() for iq (purportedly, the
+	 * inverse of q modulo p), we also tolerate improperly large
+	 * values for this parameter.
+	 */
+	t1 = (uint32_t *)(tmp + 4 * fwlen);
+	t2 = (uint32_t *)(tmp + 5 * fwlen);
+	br_i31_reduce(t2, s2, mp);
+	br_i31_add(s1, mp, br_i31_sub(s1, t2, 1));
+	br_i31_to_monty(s1, mp);
+	br_i31_decode_reduce(t1, sk->iq, sk->iqlen, mp);
+	br_i31_montymul(t2, s1, t1, mp, p0i);
+
+	/*
+	 * h is now in t2. We compute the final result:
+	 *   s = s2 + q*h
+	 * All these operations are non-modular.
+	 *
+	 * We need mq, s2 and t2. We use the t3 buffer as destination.
+	 * The buffers mp, s1 and t1 are no longer needed, so we can
+	 * reuse them for t3. Moreover, the first step of the computation
+	 * is to copy s2 into t3, after which s2 is not needed. Right
+	 * now, mq is in slot 0, s2 is in slot 1, and t2 is in slot 5.
+	 * Therefore, we have ample room for t3 by simply using s2.
+	 */
+	t3 = s2;
+	br_i31_mulacc(t3, mq, t2);
+
+	/*
+	 * Encode the result. Since we already checked the value of xlen,
+	 * we can just use it right away.
+	 */
+	br_i31_encode(x, xlen, t3);
+
+	/*
+	 * The only error conditions remaining at that point are invalid
+	 * values for p and q (even integers).
+	 */
+	return p0i & q0i & r;
+}
+
+/* see bearssl_rsa.h */
+br_rsa_private
+br_rsa_i62_private_get(void)
+{
+	return &br_rsa_i62_private;
+}
+
+#else
+
+/* see bearssl_rsa.h */
+br_rsa_private
+br_rsa_i62_private_get(void)
+{
+	return 0;
+}
+
+#endif