1  /*
  2   * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
  3   *
  4   * Permission is hereby granted, free of charge, to any person obtaining 
  5   * a copy of this software and associated documentation files (the
  6   * "Software"), to deal in the Software without restriction, including
  7   * without limitation the rights to use, copy, modify, merge, publish,
  8   * distribute, sublicense, and/or sell copies of the Software, and to
  9   * permit persons to whom the Software is furnished to do so, subject to
 10   * the following conditions:
 11   *
 12   * The above copyright notice and this permission notice shall be 
 13   * included in all copies or substantial portions of the Software.
 14   *
 15   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
 16   * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 17   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
 18   * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 19   * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 20   * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 21   * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 22   * SOFTWARE.
 23   */
 24  
 25  #include "inner.h"
 26  
 27  #if BR_INT128 || BR_UMUL128
 28  
 29  /*
 30   * As a strict minimum, we need four buffers that can hold a
 31   * modular integer. But TLEN is expressed in 64-bit words.
 32   */
 33  #define TLEN   (2 * (2 + ((BR_MAX_RSA_SIZE + 30) / 31)))
 34  
 35  /* see bearssl_rsa.h */
 36  uint32_t
 37  br_rsa_i62_public(unsigned char *x, size_t xlen,
 38  	const br_rsa_public_key *pk)
 39  {
 40  	const unsigned char *n;
 41  	size_t nlen;
 42  	uint64_t tmp[TLEN];
 43  	uint32_t *m, *a;
 44  	size_t fwlen;
 45  	long z;
 46  	uint32_t m0i, r;
 47  
 48  	/*
 49  	 * Get the actual length of the modulus, and see if it fits within
 50  	 * our stack buffer. We also check that the length of x[] is valid.
 51  	 */
 52  	n = pk->n;
 53  	nlen = pk->nlen;
 54  	while (nlen > 0 && *n == 0) {
 55  		n ++;
 56  		nlen --;
 57  	}
 58  	if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) {
 59  		return 0;
 60  	}
 61  	z = (long)nlen << 3;
 62  	fwlen = 1;
 63  	while (z > 0) {
 64  		z -= 31;
 65  		fwlen ++;
 66  	}
 67  	/*
 68  	 * Convert fwlen to a count in 62-bit words.
 69  	 */
 70  	fwlen = (fwlen + 1) >> 1;
 71  
 72  	/*
 73  	 * The modulus gets decoded into m[].
 74  	 * The value to exponentiate goes into a[].
 75  	 */
 76  	m = (uint32_t *)tmp;
 77  	a = (uint32_t *)(tmp + fwlen);
 78  
 79  	/*
 80  	 * Decode the modulus.
 81  	 */
 82  	br_i31_decode(m, n, nlen);
 83  	m0i = br_i31_ninv31(m[1]);
 84  
 85  	/*
 86  	 * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be
 87  	 * an odd integer.
 88  	 */
 89  	r = m0i & 1;
 90  
 91  	/*
 92  	 * Decode x[] into a[]; we also check that its value is proper.
 93  	 */
 94  	r &= br_i31_decode_mod(a, x, xlen, m);
 95  
 96  	/*
 97  	 * Compute the modular exponentiation.
 98  	 */
 99  	br_i62_modpow_opt(a, pk->e, pk->elen, m, m0i,
100  		tmp + 2 * fwlen, TLEN - 2 * fwlen);
101  
102  	/*
103  	 * Encode the result.
104  	 */
105  	br_i31_encode(x, xlen, a);
106  	return r;
107  }
108  
109  /* see bearssl_rsa.h */
110  br_rsa_public
111  br_rsa_i62_public_get(void)
112  {
113  	return &br_rsa_i62_public;
114  }
115  
116  #else
117  
118  /* see bearssl_rsa.h */
119  br_rsa_public
120  br_rsa_i62_public_get(void)
121  {
122  	return 0;
123  }
124  
125  #endif