/*++ /* NAME /* tls_dh /* SUMMARY /* Diffie-Hellman parameter support /* SYNOPSIS /* #define TLS_INTERNAL /* #include /* /* void tls_set_dh_from_file(path) /* const char *path; /* /* void tls_auto_groups(ctx, eecdh, ffdhe) /* SSL_CTX *ctx; /* char *eecdh; /* char *ffdhe; /* /* void tls_tmp_dh(ctx, useauto) /* SSL_CTX *ctx; /* int useauto; /* DESCRIPTION /* This module maintains parameters for Diffie-Hellman key generation. /* /* tls_tmp_dh() returns the configured or compiled-in FFDHE /* group parameters. The useauto argument enables OpenSSL-builtin group /* selection in preference to our own compiled-in group. This may /* interoperate better with overly strict peers that accept only /* "standard" groups. /* /* tls_set_dh_from_file() overrides compiled-in DH parameters /* with those specified in the named files. The file format /* is as expected by the PEM_read_DHparams() routine. /* /* tls_auto_groups() enables negotiation of the most preferred key /* exchange group among those specified by the "eecdh" and "ffdhe" /* arguments. The "ffdhe" argument is only used with OpenSSL 3.0 /* and later, and applies to TLS 1.3 and up. /* DIAGNOSTICS /* In case of error, tls_set_dh_from_file() logs a warning and /* ignores the request. /* LICENSE /* .ad /* .fi /* This software is free. You can do with it whatever you want. /* The original author kindly requests that you acknowledge /* the use of his software. /* AUTHOR(S) /* Originally written by: /* Lutz Jaenicke /* BTU Cottbus /* Allgemeine Elektrotechnik /* Universitaetsplatz 3-4 /* D-03044 Cottbus, Germany /* /* Updated by: /* Wietse Venema /* IBM T.J. Watson Research /* P.O. Box 704 /* Yorktown Heights, NY 10598, USA /*--*/ /* System library. */ #include #ifdef USE_TLS #include /* Utility library. */ #include #include #include /* * Global library */ #include /* TLS library. */ #define TLS_INTERNAL #include #include #ifndef OPENSSL_NO_ECDH #include #endif #if OPENSSL_VERSION_PREREQ(3,0) #include #endif /* Application-specific. */ /* * Compiled-in FFDHE (finite-field ephemeral Diffie-Hellman) parameters. * Used when no parameters are explicitly loaded from a site-specific file. * * With OpenSSL 3.0 and later when no explicit parameter file is specified by * the administrator (or the setting is "auto"), we delegate group selection * to OpenSSL via SSL_CTX_set_dh_auto(3). * * Using an ASN.1 DER encoding avoids the need to explicitly manipulate the * internal representation of DH parameter objects. * * The FFDHE group is now 2048-bit, as 1024 bits is increasingly considered to * weak by clients. When greater security is required, use EECDH. */ /*- * Generated via: * $ openssl dhparam -2 -outform DER 2048 2>/dev/null | * hexdump -ve '/1 "0x%02x, "' | fmt -73 * TODO: generate at compile-time. But that is no good for the majority of * sites that install pre-compiled binaries, and breaks reproducible builds. * Instead, generate at installation time and use main.cf configuration. */ static unsigned char builtin_der[] = { 0x30, 0x82, 0x01, 0x08, 0x02, 0x82, 0x01, 0x01, 0x00, 0xec, 0x02, 0x7b, 0x74, 0xc6, 0xd4, 0xb4, 0x89, 0x68, 0xfd, 0xbc, 0xe0, 0x82, 0xae, 0xd6, 0xf1, 0x4d, 0x93, 0xaa, 0x47, 0x07, 0x84, 0x3d, 0x86, 0xf8, 0x47, 0xf7, 0xdf, 0x08, 0x7b, 0xca, 0x04, 0xa4, 0x72, 0xec, 0x11, 0xe2, 0x38, 0x43, 0xb7, 0x94, 0xab, 0xaf, 0xe2, 0x85, 0x59, 0x43, 0x4e, 0x71, 0x85, 0xfe, 0x52, 0x0c, 0xe0, 0x1c, 0xb6, 0xc7, 0xb0, 0x1b, 0x06, 0xb3, 0x4d, 0x1b, 0x4f, 0xf6, 0x4b, 0x45, 0xbd, 0x1d, 0xb8, 0xe4, 0xa4, 0x48, 0x09, 0x28, 0x19, 0xd7, 0xce, 0xb1, 0xe5, 0x9a, 0xc4, 0x94, 0x55, 0xde, 0x4d, 0x86, 0x0f, 0x4c, 0x5e, 0x25, 0x51, 0x6c, 0x96, 0xca, 0xfa, 0xe3, 0x01, 0x69, 0x82, 0x6c, 0x8f, 0xf5, 0xe7, 0x0e, 0xb7, 0x8e, 0x52, 0xf1, 0xcf, 0x0b, 0x67, 0x10, 0xd0, 0xb3, 0x77, 0x79, 0xa4, 0xc1, 0xd0, 0x0f, 0x3f, 0xf5, 0x5c, 0x35, 0xf9, 0x46, 0xd2, 0xc7, 0xfb, 0x97, 0x6d, 0xd5, 0xbe, 0xe4, 0x8b, 0x5a, 0xf2, 0x88, 0xfa, 0x47, 0xdc, 0xc2, 0x4a, 0x4d, 0x69, 0xd3, 0x2a, 0xdf, 0x55, 0x6c, 0x5f, 0x71, 0x11, 0x1e, 0x87, 0x03, 0x68, 0xe1, 0xf4, 0x21, 0x06, 0x63, 0xd9, 0x65, 0xd4, 0x0c, 0x4d, 0xa7, 0x1f, 0x15, 0x53, 0x3a, 0x50, 0x1a, 0xf5, 0x9b, 0x50, 0x35, 0xe0, 0x16, 0xa1, 0xd7, 0xe6, 0xbf, 0xd7, 0xd9, 0xd9, 0x53, 0xe5, 0x8b, 0xf8, 0x7b, 0x45, 0x46, 0xb6, 0xac, 0x50, 0x16, 0x46, 0x42, 0xca, 0x76, 0x38, 0x4b, 0x8e, 0x83, 0xc6, 0x73, 0x13, 0x9c, 0x03, 0xd1, 0x7a, 0x3d, 0x8d, 0x99, 0x34, 0x10, 0x79, 0x67, 0x21, 0x23, 0xf9, 0x6f, 0x48, 0x9a, 0xa6, 0xde, 0xbf, 0x7f, 0x9c, 0x16, 0x53, 0xff, 0xf7, 0x20, 0x96, 0xeb, 0x34, 0xcb, 0x5b, 0x85, 0x2b, 0x7c, 0x98, 0x00, 0x23, 0x47, 0xce, 0xc2, 0x58, 0x12, 0x86, 0x2c, 0x57, 0x02, 0x01, 0x02, }; #if OPENSSL_VERSION_PREREQ(3,0) /* ------------------------------------- 3.0 API */ static EVP_PKEY *dhp = 0; /* load_builtin - load compile-time FFDHE group */ static void load_builtin(void) { EVP_PKEY *tmp = 0; OSSL_DECODER_CTX *d; const unsigned char *endp = builtin_der; size_t dlen = sizeof(builtin_der); d = OSSL_DECODER_CTX_new_for_pkey(&tmp, "DER", NULL, "DH", OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS, NULL, NULL); /* Check decode succeeds and consumes all data (final dlen == 0) */ if (d && OSSL_DECODER_from_data(d, &endp, &dlen) && tmp && !dlen) { dhp = tmp; } else { EVP_PKEY_free(tmp); msg_warn("error loading compiled-in DH parameters"); tls_print_errors(); } OSSL_DECODER_CTX_free(d); } /* tls_set_dh_from_file - set Diffie-Hellman parameters from file */ void tls_set_dh_from_file(const char *path) { FILE *fp; EVP_PKEY *tmp = 0; OSSL_DECODER_CTX *d; /* * This function is the first to set the DH parameters, but free any * prior value just in case the call sequence changes some day. */ if (dhp) { EVP_PKEY_free(dhp); dhp = 0; } if (strcmp(path, "auto") == 0) return; if ((fp = fopen(path, "r")) == 0) { msg_warn("error opening DH parameter file \"%s\": %m" " -- using compiled-in defaults", path); return; } d = OSSL_DECODER_CTX_new_for_pkey(&tmp, "PEM", NULL, "DH", OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS, NULL, NULL); if (!d || !OSSL_DECODER_from_fp(d, fp) || !tmp) { msg_warn("error decoding DH parameters from file \"%s\"" " -- using compiled-in defaults", path); tls_print_errors(); } else { dhp = tmp; } OSSL_DECODER_CTX_free(d); (void) fclose(fp); } /* tls_tmp_dh - configure FFDHE group */ void tls_tmp_dh(SSL_CTX *ctx, int useauto) { if (!dhp && !useauto) load_builtin(); if (!ctx) return; if (dhp) { EVP_PKEY *tmp = EVP_PKEY_dup(dhp); if (tmp && SSL_CTX_set0_tmp_dh_pkey(ctx, tmp) > 0) return; EVP_PKEY_free(tmp); msg_warn("error configuring explicit DH parameters"); tls_print_errors(); } else { if (SSL_CTX_set_dh_auto(ctx, 1) > 0) return; msg_warn("error configuring auto DH parameters"); tls_print_errors(); } } #else /* OPENSSL_VERSION_PREREQ(3,0) */ /* ------------------------------------- 1.1.1 API */ static DH *dhp = 0; static void load_builtin(void) { DH *tmp = 0; const unsigned char *endp = builtin_der; if (d2i_DHparams(&tmp, &endp, sizeof(builtin_der)) && sizeof(builtin_der) == endp - builtin_der) { dhp = tmp; } else { DH_free(tmp); msg_warn("error loading compiled-in DH parameters"); tls_print_errors(); } } /* tls_set_dh_from_file - set Diffie-Hellman parameters from file */ void tls_set_dh_from_file(const char *path) { FILE *fp; /* * This function is the first to set the DH parameters, but free any * prior value just in case the call sequence changes some day. */ if (dhp) { DH_free(dhp); dhp = 0; } /* * Forwards compatibility, support "auto" by using the builtin group when * OpenSSL is < 3.0 and does not support automatic FFDHE group selection. */ if (strcmp(path, "auto") == 0) return; if ((fp = fopen(path, "r")) == 0) { msg_warn("cannot load DH parameters from file %s: %m" " -- using compiled-in defaults", path); return; } if ((dhp = PEM_read_DHparams(fp, 0, 0, 0)) == 0) { msg_warn("cannot load DH parameters from file %s" " -- using compiled-in defaults", path); tls_print_errors(); } (void) fclose(fp); } /* tls_tmp_dh - configure FFDHE group */ void tls_tmp_dh(SSL_CTX *ctx, int useauto) { if (!dhp) load_builtin(); if (!ctx || !dhp || SSL_CTX_set_tmp_dh(ctx, dhp) > 0) return; msg_warn("error configuring explicit DH parameters"); tls_print_errors(); } #endif /* OPENSSL_VERSION_PREREQ(3,0) */ /* ------------------------------------- Common API */ #define AG_STAT_OK (0) #define AG_STAT_NO_GROUP (-1) /* no usable group, may retry */ #define AG_STAT_NO_RETRY (-2) /* other error, don't retry */ static int setup_auto_groups(SSL_CTX *ctx, const char *origin, const char *eecdh, const char *ffdhe) { #ifndef OPENSSL_NO_ECDH SSL_CTX *tmpctx; int *nids; int space = 10; int n = 0; char *save; char *groups; char *group; if ((tmpctx = SSL_CTX_new(TLS_method())) == 0) { msg_warn("cannot allocate temp SSL_CTX"); tls_print_errors(); return (AG_STAT_NO_RETRY); } nids = mymalloc(space * sizeof(int)); #define SETUP_AG_RETURN(val) do { \ myfree(save); \ myfree(nids); \ SSL_CTX_free(tmpctx); \ return (val); \ } while (0) groups = save = concatenate(eecdh, " ", ffdhe, NULL); if ((group = mystrtok(&groups, CHARS_COMMA_SP)) == 0) { msg_warn("no %s key exchange group - OpenSSL requires at least one", origin); SETUP_AG_RETURN(AG_STAT_NO_GROUP); } for (; group != 0; group = mystrtok(&groups, CHARS_COMMA_SP)) { int nid = EC_curve_nist2nid(group); if (nid == NID_undef) nid = OBJ_sn2nid(group); if (nid == NID_undef) nid = OBJ_ln2nid(group); if (nid == NID_undef) { msg_warn("ignoring unknown key exchange group \"%s\"", group); continue; } /* * Validate the NID by trying it as the group for a throw-away SSL * context. Silently skip unsupported code points. This way, we can * list X25519 and X448 as soon as the nids are assigned, and before * the supporting code is implemented. They'll be silently skipped * when not yet supported. */ if (SSL_CTX_set1_curves(tmpctx, &nid, 1) <= 0) { continue; } if (++n > space) { space *= 2; nids = myrealloc(nids, space * sizeof(int)); } nids[n - 1] = nid; } if (n == 0) { /* The names may be case-sensitive */ msg_warn("none of the %s key exchange groups are supported", origin); SETUP_AG_RETURN(AG_STAT_NO_GROUP); } if (SSL_CTX_set1_curves(ctx, nids, n) <= 0) { msg_warn("failed to set up the %s key exchange groups", origin); tls_print_errors(); SETUP_AG_RETURN(AG_STAT_NO_RETRY); } SETUP_AG_RETURN(AG_STAT_OK); #endif } void tls_auto_groups(SSL_CTX *ctx, const char *eecdh, const char *ffdhe) { #ifndef OPENSSL_NO_ECDH char *def_eecdh = DEF_TLS_EECDH_AUTO; #if OPENSSL_VERSION_PREREQ(3, 0) char *def_ffdhe = DEF_TLS_FFDHE_AUTO; #else char *def_ffdhe = ""; /* Has no effect prior to OpenSSL 3.0 */ ffdhe = def_ffdhe; #endif const char *origin; /* * Try the user-specified list first. If that fails (empty list or no * known group name), try again with the Postfix defaults. We assume that * group selection is mere performance tuning and not security critical. * All the groups supported for negotiation should be strong enough. */ for (origin = "configured"; /* void */ ; /* void */) { switch (setup_auto_groups(ctx, origin, eecdh, ffdhe)) { case AG_STAT_OK: return; case AG_STAT_NO_GROUP: if (strcmp(eecdh, def_eecdh) != 0 || strcmp(ffdhe, def_ffdhe) != 0) { msg_warn("using Postfix default key exchange groups instead"); origin = "Postfix default"; eecdh = def_eecdh; ffdhe = def_ffdhe; break; } /* FALLTHROUGH */ default: msg_warn("using OpenSSL default key exchange groups instead"); return; } } #endif } #ifdef TEST int main(int unused_argc, char **unused_argv) { tls_tmp_dh(0, 0); return (dhp == 0); } #endif #endif