2 * Helper functions for the RSA module
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4 * Copyright (C) 2006-2017, ARM Limited, All Rights Reserved
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5 * SPDX-License-Identifier: Apache-2.0
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7 * Licensed under the Apache License, Version 2.0 (the "License"); you may
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8 * not use this file except in compliance with the License.
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9 * You may obtain a copy of the License at
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11 * http://www.apache.org/licenses/LICENSE-2.0
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13 * Unless required by applicable law or agreed to in writing, software
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14 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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15 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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16 * See the License for the specific language governing permissions and
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17 * limitations under the License.
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19 * This file is part of mbed TLS (https://tls.mbed.org)
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23 #if !defined(MBEDTLS_CONFIG_FILE)
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24 #include "mbedtls/config.h"
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26 #include MBEDTLS_CONFIG_FILE
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29 #if defined(MBEDTLS_RSA_C)
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31 #include "mbedtls/rsa.h"
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32 #include "mbedtls/bignum.h"
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33 #include "mbedtls/rsa_internal.h"
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36 * Compute RSA prime factors from public and private exponents
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38 * Summary of algorithm:
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39 * Setting F := lcm(P-1,Q-1), the idea is as follows:
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41 * (a) For any 1 <= X < N with gcd(X,N)=1, we have X^F = 1 modulo N, so X^(F/2)
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42 * is a square root of 1 in Z/NZ. Since Z/NZ ~= Z/PZ x Z/QZ by CRT and the
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43 * square roots of 1 in Z/PZ and Z/QZ are +1 and -1, this leaves the four
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44 * possibilities X^(F/2) = (+-1, +-1). If it happens that X^(F/2) = (-1,+1)
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45 * or (+1,-1), then gcd(X^(F/2) + 1, N) will be equal to one of the prime
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48 * (b) If we don't know F/2 but (F/2) * K for some odd (!) K, then the same
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49 * construction still applies since (-)^K is the identity on the set of
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50 * roots of 1 in Z/NZ.
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52 * The public and private key primitives (-)^E and (-)^D are mutually inverse
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53 * bijections on Z/NZ if and only if (-)^(DE) is the identity on Z/NZ, i.e.
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54 * if and only if DE - 1 is a multiple of F, say DE - 1 = F * L.
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55 * Splitting L = 2^t * K with K odd, we have
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57 * DE - 1 = FL = (F/2) * (2^(t+1)) * K,
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59 * so (F / 2) * K is among the numbers
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61 * (DE - 1) >> 1, (DE - 1) >> 2, ..., (DE - 1) >> ord
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63 * where ord is the order of 2 in (DE - 1).
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64 * We can therefore iterate through these numbers apply the construction
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65 * of (a) and (b) above to attempt to factor N.
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68 int mbedtls_rsa_deduce_primes( mbedtls_mpi const *N,
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69 mbedtls_mpi const *E, mbedtls_mpi const *D,
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70 mbedtls_mpi *P, mbedtls_mpi *Q )
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74 uint16_t attempt; /* Number of current attempt */
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75 uint16_t iter; /* Number of squares computed in the current attempt */
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77 uint16_t order; /* Order of 2 in DE - 1 */
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79 mbedtls_mpi T; /* Holds largest odd divisor of DE - 1 */
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80 mbedtls_mpi K; /* Temporary holding the current candidate */
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82 const unsigned char primes[] = { 2,
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83 3, 5, 7, 11, 13, 17, 19, 23,
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84 29, 31, 37, 41, 43, 47, 53, 59,
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85 61, 67, 71, 73, 79, 83, 89, 97,
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86 101, 103, 107, 109, 113, 127, 131, 137,
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87 139, 149, 151, 157, 163, 167, 173, 179,
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88 181, 191, 193, 197, 199, 211, 223, 227,
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89 229, 233, 239, 241, 251
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92 const size_t num_primes = sizeof( primes ) / sizeof( *primes );
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94 if( P == NULL || Q == NULL || P->p != NULL || Q->p != NULL )
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95 return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
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97 if( mbedtls_mpi_cmp_int( N, 0 ) <= 0 ||
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98 mbedtls_mpi_cmp_int( D, 1 ) <= 0 ||
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99 mbedtls_mpi_cmp_mpi( D, N ) >= 0 ||
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100 mbedtls_mpi_cmp_int( E, 1 ) <= 0 ||
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101 mbedtls_mpi_cmp_mpi( E, N ) >= 0 )
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103 return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
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107 * Initializations and temporary changes
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110 mbedtls_mpi_init( &K );
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111 mbedtls_mpi_init( &T );
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114 MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T, D, E ) );
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115 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &T, &T, 1 ) );
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117 if( ( order = (uint16_t) mbedtls_mpi_lsb( &T ) ) == 0 )
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119 ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
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123 /* After this operation, T holds the largest odd divisor of DE - 1. */
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124 MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &T, order ) );
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130 /* Skip trying 2 if N == 1 mod 8 */
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132 if( N->p[0] % 8 == 1 )
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135 for( ; attempt < num_primes; ++attempt )
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137 mbedtls_mpi_lset( &K, primes[attempt] );
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139 /* Check if gcd(K,N) = 1 */
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140 MBEDTLS_MPI_CHK( mbedtls_mpi_gcd( P, &K, N ) );
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141 if( mbedtls_mpi_cmp_int( P, 1 ) != 0 )
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144 /* Go through K^T + 1, K^(2T) + 1, K^(4T) + 1, ...
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145 * and check whether they have nontrivial GCD with N. */
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146 MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &K, &K, &T, N,
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147 Q /* temporarily use Q for storing Montgomery
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148 * multiplication helper values */ ) );
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150 for( iter = 1; iter <= order; ++iter )
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152 /* If we reach 1 prematurely, there's no point
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153 * in continuing to square K */
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154 if( mbedtls_mpi_cmp_int( &K, 1 ) == 0 )
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157 MBEDTLS_MPI_CHK( mbedtls_mpi_add_int( &K, &K, 1 ) );
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158 MBEDTLS_MPI_CHK( mbedtls_mpi_gcd( P, &K, N ) );
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160 if( mbedtls_mpi_cmp_int( P, 1 ) == 1 &&
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161 mbedtls_mpi_cmp_mpi( P, N ) == -1 )
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164 * Have found a nontrivial divisor P of N.
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168 MBEDTLS_MPI_CHK( mbedtls_mpi_div_mpi( Q, NULL, N, P ) );
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172 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &K, &K, 1 ) );
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173 MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &K, &K, &K ) );
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174 MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &K, &K, N ) );
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178 * If we get here, then either we prematurely aborted the loop because
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179 * we reached 1, or K holds primes[attempt]^(DE - 1) mod N, which must
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180 * be 1 if D,E,N were consistent.
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181 * Check if that's the case and abort if not, to avoid very long,
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182 * yet eventually failing, computations if N,D,E were not sane.
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184 if( mbedtls_mpi_cmp_int( &K, 1 ) != 0 )
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190 ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
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194 mbedtls_mpi_free( &K );
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195 mbedtls_mpi_free( &T );
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200 * Given P, Q and the public exponent E, deduce D.
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201 * This is essentially a modular inversion.
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203 int mbedtls_rsa_deduce_private_exponent( mbedtls_mpi const *P,
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204 mbedtls_mpi const *Q,
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205 mbedtls_mpi const *E,
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211 if( D == NULL || mbedtls_mpi_cmp_int( D, 0 ) != 0 )
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212 return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
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214 if( mbedtls_mpi_cmp_int( P, 1 ) <= 0 ||
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215 mbedtls_mpi_cmp_int( Q, 1 ) <= 0 ||
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216 mbedtls_mpi_cmp_int( E, 0 ) == 0 )
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218 return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
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221 mbedtls_mpi_init( &K );
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222 mbedtls_mpi_init( &L );
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224 /* Temporarily put K := P-1 and L := Q-1 */
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225 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &K, P, 1 ) );
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226 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &L, Q, 1 ) );
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228 /* Temporarily put D := gcd(P-1, Q-1) */
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229 MBEDTLS_MPI_CHK( mbedtls_mpi_gcd( D, &K, &L ) );
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231 /* K := LCM(P-1, Q-1) */
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232 MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &K, &K, &L ) );
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233 MBEDTLS_MPI_CHK( mbedtls_mpi_div_mpi( &K, NULL, &K, D ) );
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235 /* Compute modular inverse of E in LCM(P-1, Q-1) */
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236 MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( D, E, &K ) );
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240 mbedtls_mpi_free( &K );
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241 mbedtls_mpi_free( &L );
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247 * Check that RSA CRT parameters are in accordance with core parameters.
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249 int mbedtls_rsa_validate_crt( const mbedtls_mpi *P, const mbedtls_mpi *Q,
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250 const mbedtls_mpi *D, const mbedtls_mpi *DP,
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251 const mbedtls_mpi *DQ, const mbedtls_mpi *QP )
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256 mbedtls_mpi_init( &K );
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257 mbedtls_mpi_init( &L );
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259 /* Check that DP - D == 0 mod P - 1 */
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264 ret = MBEDTLS_ERR_RSA_BAD_INPUT_DATA;
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268 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &K, P, 1 ) );
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269 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &L, DP, D ) );
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270 MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &L, &L, &K ) );
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272 if( mbedtls_mpi_cmp_int( &L, 0 ) != 0 )
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274 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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279 /* Check that DQ - D == 0 mod Q - 1 */
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284 ret = MBEDTLS_ERR_RSA_BAD_INPUT_DATA;
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288 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &K, Q, 1 ) );
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289 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &L, DQ, D ) );
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290 MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &L, &L, &K ) );
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292 if( mbedtls_mpi_cmp_int( &L, 0 ) != 0 )
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294 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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299 /* Check that QP * Q - 1 == 0 mod P */
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302 if( P == NULL || Q == NULL )
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304 ret = MBEDTLS_ERR_RSA_BAD_INPUT_DATA;
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308 MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &K, QP, Q ) );
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309 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &K, &K, 1 ) );
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310 MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &K, &K, P ) );
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311 if( mbedtls_mpi_cmp_int( &K, 0 ) != 0 )
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313 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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320 /* Wrap MPI error codes by RSA check failure error code */
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322 ret != MBEDTLS_ERR_RSA_KEY_CHECK_FAILED &&
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323 ret != MBEDTLS_ERR_RSA_BAD_INPUT_DATA )
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325 ret += MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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328 mbedtls_mpi_free( &K );
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329 mbedtls_mpi_free( &L );
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335 * Check that core RSA parameters are sane.
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337 int mbedtls_rsa_validate_params( const mbedtls_mpi *N, const mbedtls_mpi *P,
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338 const mbedtls_mpi *Q, const mbedtls_mpi *D,
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339 const mbedtls_mpi *E,
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340 int (*f_rng)(void *, unsigned char *, size_t),
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346 mbedtls_mpi_init( &K );
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347 mbedtls_mpi_init( &L );
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350 * Step 1: If PRNG provided, check that P and Q are prime
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353 #if defined(MBEDTLS_GENPRIME)
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355 * When generating keys, the strongest security we support aims for an error
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356 * rate of at most 2^-100 and we are aiming for the same certainty here as
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359 if( f_rng != NULL && P != NULL &&
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360 ( ret = mbedtls_mpi_is_prime_ext( P, 50, f_rng, p_rng ) ) != 0 )
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362 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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366 if( f_rng != NULL && Q != NULL &&
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367 ( ret = mbedtls_mpi_is_prime_ext( Q, 50, f_rng, p_rng ) ) != 0 )
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369 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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375 #endif /* MBEDTLS_GENPRIME */
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378 * Step 2: Check that 1 < N = P * Q
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381 if( P != NULL && Q != NULL && N != NULL )
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383 MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &K, P, Q ) );
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384 if( mbedtls_mpi_cmp_int( N, 1 ) <= 0 ||
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385 mbedtls_mpi_cmp_mpi( &K, N ) != 0 )
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387 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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393 * Step 3: Check and 1 < D, E < N if present.
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396 if( N != NULL && D != NULL && E != NULL )
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398 if ( mbedtls_mpi_cmp_int( D, 1 ) <= 0 ||
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399 mbedtls_mpi_cmp_int( E, 1 ) <= 0 ||
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400 mbedtls_mpi_cmp_mpi( D, N ) >= 0 ||
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401 mbedtls_mpi_cmp_mpi( E, N ) >= 0 )
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403 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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409 * Step 4: Check that D, E are inverse modulo P-1 and Q-1
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412 if( P != NULL && Q != NULL && D != NULL && E != NULL )
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414 if( mbedtls_mpi_cmp_int( P, 1 ) <= 0 ||
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415 mbedtls_mpi_cmp_int( Q, 1 ) <= 0 )
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417 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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421 /* Compute DE-1 mod P-1 */
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422 MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &K, D, E ) );
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423 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &K, &K, 1 ) );
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424 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &L, P, 1 ) );
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425 MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &K, &K, &L ) );
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426 if( mbedtls_mpi_cmp_int( &K, 0 ) != 0 )
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428 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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432 /* Compute DE-1 mod Q-1 */
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433 MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &K, D, E ) );
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434 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &K, &K, 1 ) );
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435 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &L, Q, 1 ) );
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436 MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &K, &K, &L ) );
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437 if( mbedtls_mpi_cmp_int( &K, 0 ) != 0 )
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439 ret = MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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446 mbedtls_mpi_free( &K );
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447 mbedtls_mpi_free( &L );
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449 /* Wrap MPI error codes by RSA check failure error code */
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450 if( ret != 0 && ret != MBEDTLS_ERR_RSA_KEY_CHECK_FAILED )
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452 ret += MBEDTLS_ERR_RSA_KEY_CHECK_FAILED;
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458 int mbedtls_rsa_deduce_crt( const mbedtls_mpi *P, const mbedtls_mpi *Q,
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459 const mbedtls_mpi *D, mbedtls_mpi *DP,
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460 mbedtls_mpi *DQ, mbedtls_mpi *QP )
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464 mbedtls_mpi_init( &K );
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466 /* DP = D mod P-1 */
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469 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &K, P, 1 ) );
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470 MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( DP, D, &K ) );
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473 /* DQ = D mod Q-1 */
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476 MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &K, Q, 1 ) );
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477 MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( DQ, D, &K ) );
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480 /* QP = Q^{-1} mod P */
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483 MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( QP, Q, P ) );
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487 mbedtls_mpi_free( &K );
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492 #endif /* MBEDTLS_RSA_C */
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