/* * Diffie-Hellman-Merkle key exchange * * Copyright (C) 2006-2015, ARM Limited, All Rights Reserved * SPDX-License-Identifier: Apache-2.0 * * Licensed under the Apache License, Version 2.0 (the "License"); you may * not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. * * This file is part of mbed TLS (https://tls.mbed.org) */ /* * The following sources were referenced in the design of this implementation * of the Diffie-Hellman-Merkle algorithm: * * [1] Handbook of Applied Cryptography - 1997, Chapter 12 * Menezes, van Oorschot and Vanstone * */ #if !defined(MBEDTLS_CONFIG_FILE) #include "mbedtls/config.h" #else #include MBEDTLS_CONFIG_FILE #endif #if defined(MBEDTLS_DHM_C) #include "mbedtls/dhm.h" #include #if defined(MBEDTLS_PEM_PARSE_C) #include "mbedtls/pem.h" #endif #if defined(MBEDTLS_ASN1_PARSE_C) #include "mbedtls/asn1.h" #endif #if defined(MBEDTLS_PLATFORM_C) #include "mbedtls/platform.h" #else #include #include #define mbedtls_printf printf #define mbedtls_calloc calloc #define mbedtls_free free #endif #include "arc4_alt.h" /* * helper to validate the mbedtls_mpi size and import it */ static int dhm_read_bignum( mbedtls_mpi *X, unsigned char **p, const unsigned char *end ) { int ret, n; if( end - *p < 2 ) return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA ); n = ( (*p)[0] << 8 ) | (*p)[1]; (*p) += 2; if( (int)( end - *p ) < n ) return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA ); if( ( ret = mbedtls_mpi_read_binary( X, *p, n ) ) != 0 ) return( MBEDTLS_ERR_DHM_READ_PARAMS_FAILED + ret ); (*p) += n; return( 0 ); } /* * Verify sanity of parameter with regards to P * * Parameter should be: 2 <= public_param <= P - 2 * * For more information on the attack, see: * http://www.cl.cam.ac.uk/~rja14/Papers/psandqs.pdf * http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2005-2643 */ static int dhm_check_range( const mbedtls_mpi *param, const mbedtls_mpi *P ) { mbedtls_mpi L, U; int ret = MBEDTLS_ERR_DHM_BAD_INPUT_DATA; mbedtls_mpi_init( &L ); mbedtls_mpi_init( &U ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &L, 2 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &U, P, 2 ) ); if( mbedtls_mpi_cmp_mpi( param, &L ) >= 0 && mbedtls_mpi_cmp_mpi( param, &U ) <= 0 ) { ret = 0; } cleanup: mbedtls_mpi_free( &L ); mbedtls_mpi_free( &U ); return( ret ); } void mbedtls_dhm_init( mbedtls_dhm_context *ctx ) { memset( ctx, 0, sizeof( mbedtls_dhm_context ) ); } /* * Parse the ServerKeyExchange parameters */ int mbedtls_dhm_read_params( mbedtls_dhm_context *ctx, unsigned char **p, const unsigned char *end ) { int ret; if( ( ret = dhm_read_bignum( &ctx->P, p, end ) ) != 0 || ( ret = dhm_read_bignum( &ctx->G, p, end ) ) != 0 || ( ret = dhm_read_bignum( &ctx->GY, p, end ) ) != 0 ) return( ret ); if( ( ret = dhm_check_range( &ctx->GY, &ctx->P ) ) != 0 ) return( ret ); ctx->len = mbedtls_mpi_size( &ctx->P ); return( 0 ); } /* * Setup and write the ServerKeyExchange parameters */ int mbedtls_dhm_make_params( mbedtls_dhm_context *ctx, int x_size, unsigned char *output, size_t *olen, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret, count = 0; size_t n1, n2, n3; unsigned char *p; if( mbedtls_mpi_cmp_int( &ctx->P, 0 ) == 0 ) return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA ); /* * Generate X as large as possible ( < P ) */ do { MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &ctx->X, x_size, f_rng, p_rng ) ); while( mbedtls_mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 ) MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &ctx->X, 1 ) ); if( count++ > 10 ) return( MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED ); } while( dhm_check_range( &ctx->X, &ctx->P ) != 0 ); /* * Calculate GX = G^X mod P */ MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X, &ctx->P , &ctx->RP ) ); if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 ) return( ret ); /* * export P, G, GX */ #define DHM_MPI_EXPORT(X,n) \ MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( X, p + 2, n ) ); \ *p++ = (unsigned char)( n >> 8 ); \ *p++ = (unsigned char)( n ); p += n; n1 = mbedtls_mpi_size( &ctx->P ); n2 = mbedtls_mpi_size( &ctx->G ); n3 = mbedtls_mpi_size( &ctx->GX ); p = output; DHM_MPI_EXPORT( &ctx->P , n1 ); DHM_MPI_EXPORT( &ctx->G , n2 ); DHM_MPI_EXPORT( &ctx->GX, n3 ); *olen = p - output; ctx->len = n1; cleanup: if( ret != 0 ) return( MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED + ret ); return( 0 ); } /* * Import the peer's public value G^Y */ int mbedtls_dhm_read_public( mbedtls_dhm_context *ctx, const unsigned char *input, size_t ilen ) { int ret; if( ctx == NULL || ilen < 1 || ilen > ctx->len ) return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA ); if( ( ret = mbedtls_mpi_read_binary( &ctx->GY, input, ilen ) ) != 0 ) return( MBEDTLS_ERR_DHM_READ_PUBLIC_FAILED + ret ); return( 0 ); } /* * Create own private value X and export G^X */ int mbedtls_dhm_make_public( mbedtls_dhm_context *ctx, int x_size, unsigned char *output, size_t olen, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret, count = 0; if( ctx == NULL || olen < 1 || olen > ctx->len ) return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA ); if( mbedtls_mpi_cmp_int( &ctx->P, 0 ) == 0 ) return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA ); /* * generate X and calculate GX = G^X mod P */ do { MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &ctx->X, x_size, f_rng, p_rng ) ); while( mbedtls_mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 ) MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &ctx->X, 1 ) ); if( count++ > 10 ) return( MBEDTLS_ERR_DHM_MAKE_PUBLIC_FAILED ); } while( dhm_check_range( &ctx->X, &ctx->P ) != 0 ); MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X, &ctx->P , &ctx->RP ) ); if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 ) return( ret ); MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &ctx->GX, output, olen ) ); cleanup: if( ret != 0 ) return( MBEDTLS_ERR_DHM_MAKE_PUBLIC_FAILED + ret ); return( 0 ); } /* * Use the blinding method and optimisation suggested in section 10 of: * KOCHER, Paul C. Timing attacks on implementations of Diffie-Hellman, RSA, * DSS, and other systems. In : Advances in Cryptology-CRYPTO'96. Springer * Berlin Heidelberg, 1996. p. 104-113. */ static int dhm_update_blinding( mbedtls_dhm_context *ctx, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret, count; /* * Don't use any blinding the first time a particular X is used, * but remember it to use blinding next time. */ if( mbedtls_mpi_cmp_mpi( &ctx->X, &ctx->pX ) != 0 ) { MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &ctx->pX, &ctx->X ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &ctx->Vi, 1 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &ctx->Vf, 1 ) ); return( 0 ); } /* * Ok, we need blinding. Can we re-use existing values? * If yes, just update them by squaring them. */ if( mbedtls_mpi_cmp_int( &ctx->Vi, 1 ) != 0 ) { MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &ctx->Vi ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->P ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ctx->Vf, &ctx->Vf, &ctx->Vf ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->Vf, &ctx->Vf, &ctx->P ) ); return( 0 ); } /* * We need to generate blinding values from scratch */ /* Vi = random( 2, P-1 ) */ count = 0; do { MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &ctx->Vi, mbedtls_mpi_size( &ctx->P ), f_rng, p_rng ) ); while( mbedtls_mpi_cmp_mpi( &ctx->Vi, &ctx->P ) >= 0 ) MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &ctx->Vi, 1 ) ); if( count++ > 10 ) return( MBEDTLS_ERR_MPI_NOT_ACCEPTABLE ); } while( mbedtls_mpi_cmp_int( &ctx->Vi, 1 ) <= 0 ); /* Vf = Vi^-X mod P */ MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &ctx->Vf, &ctx->Vi, &ctx->P ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->Vf, &ctx->Vf, &ctx->X, &ctx->P, &ctx->RP ) ); cleanup: return( ret ); } /* * Derive and export the shared secret (G^Y)^X mod P */ int mbedtls_dhm_calc_secret( mbedtls_dhm_context *ctx, unsigned char *output, size_t output_size, size_t *olen, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret; mbedtls_mpi GYb; if( ctx == NULL || output_size < ctx->len ) return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA ); if( ( ret = dhm_check_range( &ctx->GY, &ctx->P ) ) != 0 ) return( ret ); mbedtls_mpi_init( &GYb ); /* Blind peer's value */ if( f_rng != NULL ) { MBEDTLS_MPI_CHK( dhm_update_blinding( ctx, f_rng, p_rng ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &GYb, &ctx->GY, &ctx->Vi ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &GYb, &GYb, &ctx->P ) ); } else MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &GYb, &ctx->GY ) ); /* Do modular exponentiation */ MBEDTLS_MPI_CHK( mbedtls_mpi_exp_mod( &ctx->K, &GYb, &ctx->X, &ctx->P, &ctx->RP ) ); /* Unblind secret value */ if( f_rng != NULL ) { MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ctx->K, &ctx->K, &ctx->Vf ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &ctx->K, &ctx->K, &ctx->P ) ); } *olen = mbedtls_mpi_size( &ctx->K ); MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &ctx->K, output, *olen ) ); cleanup: mbedtls_mpi_free( &GYb ); if( ret != 0 ) return( MBEDTLS_ERR_DHM_CALC_SECRET_FAILED + ret ); return( 0 ); } /* * Free the components of a DHM key */ void mbedtls_dhm_free( mbedtls_dhm_context *ctx ) { mbedtls_mpi_free( &ctx->pX); mbedtls_mpi_free( &ctx->Vf ); mbedtls_mpi_free( &ctx->Vi ); mbedtls_mpi_free( &ctx->RP ); mbedtls_mpi_free( &ctx->K ); mbedtls_mpi_free( &ctx->GY ); mbedtls_mpi_free( &ctx->GX ); mbedtls_mpi_free( &ctx->X ); mbedtls_mpi_free( &ctx->G ); mbedtls_mpi_free( &ctx->P ); mbedtls_zeroize( ctx, sizeof( mbedtls_dhm_context ) ); } #if defined(MBEDTLS_ASN1_PARSE_C) /* * Parse DHM parameters */ int mbedtls_dhm_parse_dhm( mbedtls_dhm_context *dhm, const unsigned char *dhmin, size_t dhminlen ) { int ret; size_t len; unsigned char *p, *end; #if defined(MBEDTLS_PEM_PARSE_C) mbedtls_pem_context pem; mbedtls_pem_init( &pem ); /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */ if( dhminlen == 0 || dhmin[dhminlen - 1] != '\0' ) ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT; else ret = mbedtls_pem_read_buffer( &pem, "-----BEGIN DH PARAMETERS-----", "-----END DH PARAMETERS-----", dhmin, NULL, 0, &dhminlen ); if( ret == 0 ) { /* * Was PEM encoded */ dhminlen = pem.buflen; } else if( ret != MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT ) goto exit; p = ( ret == 0 ) ? pem.buf : (unsigned char *) dhmin; #else p = (unsigned char *) dhmin; #endif /* MBEDTLS_PEM_PARSE_C */ end = p + dhminlen; /* * DHParams ::= SEQUENCE { * prime INTEGER, -- P * generator INTEGER, -- g * privateValueLength INTEGER OPTIONAL * } */ if( ( ret = mbedtls_asn1_get_tag( &p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 ) { ret = MBEDTLS_ERR_DHM_INVALID_FORMAT + ret; goto exit; } end = p + len; if( ( ret = mbedtls_asn1_get_mpi( &p, end, &dhm->P ) ) != 0 || ( ret = mbedtls_asn1_get_mpi( &p, end, &dhm->G ) ) != 0 ) { ret = MBEDTLS_ERR_DHM_INVALID_FORMAT + ret; goto exit; } if( p != end ) { /* This might be the optional privateValueLength. * If so, we can cleanly discard it */ mbedtls_mpi rec; mbedtls_mpi_init( &rec ); ret = mbedtls_asn1_get_mpi( &p, end, &rec ); mbedtls_mpi_free( &rec ); if ( ret != 0 ) { ret = MBEDTLS_ERR_DHM_INVALID_FORMAT + ret; goto exit; } if ( p != end ) { ret = MBEDTLS_ERR_DHM_INVALID_FORMAT + MBEDTLS_ERR_ASN1_LENGTH_MISMATCH; goto exit; } } ret = 0; dhm->len = mbedtls_mpi_size( &dhm->P ); exit: #if defined(MBEDTLS_PEM_PARSE_C) mbedtls_pem_free( &pem ); #endif if( ret != 0 ) mbedtls_dhm_free( dhm ); return( ret ); } #if defined(MBEDTLS_FS_IO) /* * Load all data from a file into a given buffer. * * The file is expected to contain either PEM or DER encoded data. * A terminating null byte is always appended. It is included in the announced * length only if the data looks like it is PEM encoded. */ static int load_file( const char *path, unsigned char **buf, size_t *n ) { FILE *f; long size; if( ( f = fopen( path, "rb" ) ) == NULL ) return( MBEDTLS_ERR_DHM_FILE_IO_ERROR ); fseek( f, 0, SEEK_END ); if( ( size = ftell( f ) ) == -1 ) { fclose( f ); return( MBEDTLS_ERR_DHM_FILE_IO_ERROR ); } fseek( f, 0, SEEK_SET ); *n = (size_t) size; if( *n + 1 == 0 || ( *buf = (unsigned char*)mbedtls_calloc( 1, *n + 1 ) ) == NULL ) { fclose( f ); return( MBEDTLS_ERR_DHM_ALLOC_FAILED ); } if( fread( *buf, 1, *n, f ) != *n ) { fclose( f ); mbedtls_free( *buf ); return( MBEDTLS_ERR_DHM_FILE_IO_ERROR ); } fclose( f ); (*buf)[*n] = '\0'; if( strstr( (const char *) *buf, "-----BEGIN " ) != NULL ) ++*n; return( 0 ); } /* * Load and parse DHM parameters */ int mbedtls_dhm_parse_dhmfile( mbedtls_dhm_context *dhm, const char *path ) { int ret; size_t n; unsigned char *buf; if( ( ret = load_file( path, &buf, &n ) ) != 0 ) return( ret ); ret = mbedtls_dhm_parse_dhm( dhm, buf, n ); mbedtls_zeroize( buf, n ); mbedtls_free( buf ); return( ret ); } #endif /* MBEDTLS_FS_IO */ #endif /* MBEDTLS_ASN1_PARSE_C */ #if defined(MBEDTLS_SELF_TEST) static const char mbedtls_test_dhm_params[] = "-----BEGIN DH PARAMETERS-----\r\n" "MIGHAoGBAJ419DBEOgmQTzo5qXl5fQcN9TN455wkOL7052HzxxRVMyhYmwQcgJvh\r\n" "1sa18fyfR9OiVEMYglOpkqVoGLN7qd5aQNNi5W7/C+VBdHTBJcGZJyyP5B3qcz32\r\n" "9mLJKudlVudV0Qxk5qUJaPZ/xupz0NyoVpviuiBOI1gNi8ovSXWzAgEC\r\n" "-----END DH PARAMETERS-----\r\n"; static const size_t mbedtls_test_dhm_params_len = sizeof( mbedtls_test_dhm_params ); /* * Checkup routine */ int mbedtls_dhm_self_test( int verbose ) { int ret; mbedtls_dhm_context dhm; mbedtls_dhm_init( &dhm ); if( verbose != 0 ) mbedtls_printf( " DHM parameter load: " ); if( ( ret = mbedtls_dhm_parse_dhm( &dhm, (const unsigned char *) mbedtls_test_dhm_params, mbedtls_test_dhm_params_len ) ) != 0 ) { if( verbose != 0 ) mbedtls_printf( "failed\n" ); ret = 1; goto exit; } if( verbose != 0 ) mbedtls_printf( "passed\n\n" ); exit: mbedtls_dhm_free( &dhm ); return( ret ); } #endif /* MBEDTLS_SELF_TEST */ #endif /* MBEDTLS_DHM_C */