/* * Diffie-Hellman-Merkle key exchange * * Copyright The Mbed TLS Contributors * SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */ /* * 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 * */ #include "common.h" #if defined(MBEDTLS_DHM_C) #include "mbedtls/dhm.h" #include "mbedtls/platform_util.h" #include "mbedtls/error.h" #include #if defined(MBEDTLS_PEM_PARSE_C) #include "mbedtls/pem.h" #endif #if defined(MBEDTLS_ASN1_PARSE_C) #include "mbedtls/asn1.h" #endif #include "mbedtls/platform.h" #if !defined(MBEDTLS_DHM_ALT) /* * 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 = MBEDTLS_GET_UINT16_BE(*p, 0); (*p) += 2; if ((size_t) (end - *p) < (size_t) n) { return MBEDTLS_ERR_DHM_BAD_INPUT_DATA; } if ((ret = mbedtls_mpi_read_binary(X, *p, n)) != 0) { return MBEDTLS_ERROR_ADD(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 * * This means that we need to return an error if * public_param < 2 or 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 U; int ret = 0; mbedtls_mpi_init(&U); MBEDTLS_MPI_CHK(mbedtls_mpi_sub_int(&U, P, 2)); if (mbedtls_mpi_cmp_int(param, 2) < 0 || mbedtls_mpi_cmp_mpi(param, &U) > 0) { ret = MBEDTLS_ERR_DHM_BAD_INPUT_DATA; } cleanup: mbedtls_mpi_free(&U); return ret; } void mbedtls_dhm_init(mbedtls_dhm_context *ctx) { memset(ctx, 0, sizeof(mbedtls_dhm_context)); } size_t mbedtls_dhm_get_bitlen(const mbedtls_dhm_context *ctx) { return mbedtls_mpi_bitlen(&ctx->P); } size_t mbedtls_dhm_get_len(const mbedtls_dhm_context *ctx) { return mbedtls_mpi_size(&ctx->P); } int mbedtls_dhm_get_value(const mbedtls_dhm_context *ctx, mbedtls_dhm_parameter param, mbedtls_mpi *dest) { const mbedtls_mpi *src = NULL; switch (param) { case MBEDTLS_DHM_PARAM_P: src = &ctx->P; break; case MBEDTLS_DHM_PARAM_G: src = &ctx->G; break; case MBEDTLS_DHM_PARAM_X: src = &ctx->X; break; case MBEDTLS_DHM_PARAM_GX: src = &ctx->GX; break; case MBEDTLS_DHM_PARAM_GY: src = &ctx->GY; break; case MBEDTLS_DHM_PARAM_K: src = &ctx->K; break; default: return MBEDTLS_ERR_DHM_BAD_INPUT_DATA; } return mbedtls_mpi_copy(dest, src); } /* * Parse the ServerKeyExchange parameters */ int mbedtls_dhm_read_params(mbedtls_dhm_context *ctx, unsigned char **p, const unsigned char *end) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; 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; } return 0; } /* * Pick a random R in the range [2, M-2] for blinding or key generation. */ static int dhm_random_below(mbedtls_mpi *R, const mbedtls_mpi *M, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng) { int ret; MBEDTLS_MPI_CHK(mbedtls_mpi_random(R, 3, M, f_rng, p_rng)); MBEDTLS_MPI_CHK(mbedtls_mpi_sub_int(R, R, 1)); cleanup: return ret; } static int dhm_make_common(mbedtls_dhm_context *ctx, int x_size, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng) { int ret = 0; if (mbedtls_mpi_cmp_int(&ctx->P, 0) == 0) { return MBEDTLS_ERR_DHM_BAD_INPUT_DATA; } if (x_size < 0) { return MBEDTLS_ERR_DHM_BAD_INPUT_DATA; } if ((unsigned) x_size < mbedtls_mpi_size(&ctx->P)) { MBEDTLS_MPI_CHK(mbedtls_mpi_fill_random(&ctx->X, x_size, f_rng, p_rng)); } else { /* Generate X as large as possible ( <= P - 2 ) */ ret = dhm_random_below(&ctx->X, &ctx->P, f_rng, p_rng); if (ret == MBEDTLS_ERR_MPI_NOT_ACCEPTABLE) { return MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED; } if (ret != 0) { return ret; } } /* * 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; } cleanup: return ret; } /* * 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; size_t n1, n2, n3; unsigned char *p; ret = dhm_make_common(ctx, x_size, f_rng, p_rng); if (ret != 0) { goto cleanup; } /* * Export P, G, GX. RFC 5246 §4.4 states that "leading zero octets are * not required". We omit leading zeros for compactness. */ #define DHM_MPI_EXPORT(X, n) \ do { \ MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary((X), \ p + 2, \ (n))); \ *p++ = MBEDTLS_BYTE_1(n); \ *p++ = MBEDTLS_BYTE_0(n); \ p += (n); \ } while (0) 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 = (size_t) (p - output); cleanup: if (ret != 0 && ret > -128) { ret = MBEDTLS_ERROR_ADD(MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED, ret); } return ret; } /* * Set prime modulus and generator */ int mbedtls_dhm_set_group(mbedtls_dhm_context *ctx, const mbedtls_mpi *P, const mbedtls_mpi *G) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; if ((ret = mbedtls_mpi_copy(&ctx->P, P)) != 0 || (ret = mbedtls_mpi_copy(&ctx->G, G)) != 0) { return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_DHM_SET_GROUP_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 = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; if (ilen < 1 || ilen > mbedtls_dhm_get_len(ctx)) { return MBEDTLS_ERR_DHM_BAD_INPUT_DATA; } if ((ret = mbedtls_mpi_read_binary(&ctx->GY, input, ilen)) != 0) { return MBEDTLS_ERROR_ADD(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; if (olen < 1 || olen > mbedtls_dhm_get_len(ctx)) { return MBEDTLS_ERR_DHM_BAD_INPUT_DATA; } ret = dhm_make_common(ctx, x_size, f_rng, p_rng); if (ret == MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED) { return MBEDTLS_ERR_DHM_MAKE_PUBLIC_FAILED; } if (ret != 0) { goto cleanup; } MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(&ctx->GX, output, olen)); cleanup: if (ret != 0 && ret > -128) { ret = MBEDTLS_ERROR_ADD(MBEDTLS_ERR_DHM_MAKE_PUBLIC_FAILED, ret); } return ret; } /* * 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; mbedtls_mpi R; mbedtls_mpi_init(&R); /* * 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-2 ) */ MBEDTLS_MPI_CHK(dhm_random_below(&ctx->Vi, &ctx->P, f_rng, p_rng)); /* Vf = Vi^-X mod P * First compute Vi^-1 = R * (R Vi)^-1, (avoiding leaks from inv_mod), * then elevate to the Xth power. */ MBEDTLS_MPI_CHK(dhm_random_below(&R, &ctx->P, f_rng, p_rng)); MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&ctx->Vf, &ctx->Vi, &R)); MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(&ctx->Vf, &ctx->Vf, &ctx->P)); MBEDTLS_MPI_CHK(mbedtls_mpi_inv_mod(&ctx->Vf, &ctx->Vf, &ctx->P)); MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&ctx->Vf, &ctx->Vf, &R)); MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(&ctx->Vf, &ctx->Vf, &ctx->P)); MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&ctx->Vf, &ctx->Vf, &ctx->X, &ctx->P, &ctx->RP)); cleanup: mbedtls_mpi_free(&R); 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_ERR_ERROR_CORRUPTION_DETECTED; mbedtls_mpi GYb; if (f_rng == NULL) { return MBEDTLS_ERR_DHM_BAD_INPUT_DATA; } if (output_size < mbedtls_dhm_get_len(ctx)) { 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 */ 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)); /* Do modular exponentiation */ MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&ctx->K, &GYb, &ctx->X, &ctx->P, &ctx->RP)); /* Unblind secret value */ 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)); /* Output the secret without any leading zero byte. This is mandatory * for TLS per RFC 5246 §8.1.2. */ *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_ERROR_ADD(MBEDTLS_ERR_DHM_CALC_SECRET_FAILED, ret); } return 0; } /* * Free the components of a DHM key */ void mbedtls_dhm_free(mbedtls_dhm_context *ctx) { if (ctx == NULL) { return; } 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_platform_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 = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; size_t len; unsigned char *p, *end; #if defined(MBEDTLS_PEM_PARSE_C) mbedtls_pem_context pem; #endif /* MBEDTLS_PEM_PARSE_C */ #if defined(MBEDTLS_PEM_PARSE_C) 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_ERROR_ADD(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_ERROR_ADD(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_ERROR_ADD(MBEDTLS_ERR_DHM_INVALID_FORMAT, ret); goto exit; } if (p != end) { ret = MBEDTLS_ERROR_ADD(MBEDTLS_ERR_DHM_INVALID_FORMAT, MBEDTLS_ERR_ASN1_LENGTH_MISMATCH); goto exit; } } ret = 0; 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; } /* The data loaded here is public, so don't bother disabling buffering. */ 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 = mbedtls_calloc(1, *n + 1)) == NULL) { fclose(f); return MBEDTLS_ERR_DHM_ALLOC_FAILED; } if (fread(*buf, 1, *n, f) != *n) { fclose(f); mbedtls_zeroize_and_free(*buf, *n + 1); 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 = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; 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_and_free(buf, n); return ret; } #endif /* MBEDTLS_FS_IO */ #endif /* MBEDTLS_ASN1_PARSE_C */ #endif /* MBEDTLS_DHM_ALT */ #if defined(MBEDTLS_SELF_TEST) #if defined(MBEDTLS_PEM_PARSE_C) 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"; #else /* MBEDTLS_PEM_PARSE_C */ static const char mbedtls_test_dhm_params[] = { 0x30, 0x81, 0x87, 0x02, 0x81, 0x81, 0x00, 0x9e, 0x35, 0xf4, 0x30, 0x44, 0x3a, 0x09, 0x90, 0x4f, 0x3a, 0x39, 0xa9, 0x79, 0x79, 0x7d, 0x07, 0x0d, 0xf5, 0x33, 0x78, 0xe7, 0x9c, 0x24, 0x38, 0xbe, 0xf4, 0xe7, 0x61, 0xf3, 0xc7, 0x14, 0x55, 0x33, 0x28, 0x58, 0x9b, 0x04, 0x1c, 0x80, 0x9b, 0xe1, 0xd6, 0xc6, 0xb5, 0xf1, 0xfc, 0x9f, 0x47, 0xd3, 0xa2, 0x54, 0x43, 0x18, 0x82, 0x53, 0xa9, 0x92, 0xa5, 0x68, 0x18, 0xb3, 0x7b, 0xa9, 0xde, 0x5a, 0x40, 0xd3, 0x62, 0xe5, 0x6e, 0xff, 0x0b, 0xe5, 0x41, 0x74, 0x74, 0xc1, 0x25, 0xc1, 0x99, 0x27, 0x2c, 0x8f, 0xe4, 0x1d, 0xea, 0x73, 0x3d, 0xf6, 0xf6, 0x62, 0xc9, 0x2a, 0xe7, 0x65, 0x56, 0xe7, 0x55, 0xd1, 0x0c, 0x64, 0xe6, 0xa5, 0x09, 0x68, 0xf6, 0x7f, 0xc6, 0xea, 0x73, 0xd0, 0xdc, 0xa8, 0x56, 0x9b, 0xe2, 0xba, 0x20, 0x4e, 0x23, 0x58, 0x0d, 0x8b, 0xca, 0x2f, 0x49, 0x75, 0xb3, 0x02, 0x01, 0x02 }; #endif /* MBEDTLS_PEM_PARSE_C */ 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_ERR_ERROR_CORRUPTION_DETECTED; 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 */