============ Make self-signed cert: $ openssl req -x509 -newkey ec:<(openssl ecparam -name secp384r1) -keyout serverkey.pem -out servercert.pem -nodes -sha256 -days 3650 -subj '/CN=server' Record our fingerprint in an environment variable for the client to use later: $ server_fingerprint="$(openssl x509 -in servercert.pem -noout -sha256 -fingerprint | sed 's/.*=//;s/\(.*\)/\1/')" Client side: ============ Make self-signed cert: $ openssl req -x509 -newkey ec:<(openssl ecparam -name secp384r1) -keyout clientkey.pem -out clientcert.pem -nodes -sha256 -days 3650 -subj '/CN=client' Record our fingerprint in an environment variable for the server to use later: $ client_fingerprint="$(openssl x509 -in clientcert.pem -noout -sha256 -fingerprint | sed 's/.*=//;s/\(.*\)/\1/')" Start server/client =================== Start openvpn with peer fingerprint verification: $ sudo openvpn --server 10.66.0.0 255.255.255.0 --dev tun --dh none --cert servercert.pem --key serverkey.pem --peer-fingerprint "$client_fingerprint" $ sudo openvpn --client --remote 127.0.0.1 --dev tun --cert clientcert.pem --key clientkey.pem --peer-fingerprint "$server_fingerprint" --nobind Signed-off-by: Jason A. Donenfeld Patch V2: Changes in V2 (by Arne Schwabe): - Only check peer certificates, not all cert levels, if you need multiple levels of certificate you should use a real CA - Use peer-fingerprint instead tls-verify on server side in example. - rename variable ca_file_none to verify_hash_no_ca - do no require --ca none but allow --ca simply to be absent when --peer-fingprint is present - adjust warnings/errors messages to also point to peer-fingerprint as valid verification method. - Fix mbed TLS version of not requiring CA not working Patch v3: Fix minor style. Remove unessary check of verify_hash_no_ca in ssl.c. Signed-off-by: Arne Schwabe --- src/openvpn/init.c | 1 + src/openvpn/options.c | 27 +++++++++++++++++++++------ src/openvpn/options.h | 1 + src/openvpn/ssl_common.h | 1 + src/openvpn/ssl_verify_mbedtls.c | 16 ++++++++++++++++ src/openvpn/ssl_verify_openssl.c | 2 +- 6 files changed, 41 insertions(+), 7 deletions(-) diff --git a/src/openvpn/init.c b/src/openvpn/init.c index 731b0cf2..c56dac87 100644 --- a/src/openvpn/init.c +++ b/src/openvpn/init.c @@ -2928,6 +2928,7 @@ do_init_crypto_tls(struct context *c, const unsigned int flags) to.verify_hash = options->verify_hash; to.verify_hash_algo = options->verify_hash_algo; to.verify_hash_depth = options->verify_hash_depth; + to.verify_hash_no_ca = options->verify_hash_no_ca; #ifdef ENABLE_X509ALTUSERNAME memcpy(to.x509_username_field, options->x509_username_field, sizeof(to.x509_username_field)); #else diff --git a/src/openvpn/options.c b/src/openvpn/options.c index 38ced536..4eee3a8a 100644 --- a/src/openvpn/options.c +++ b/src/openvpn/options.c @@ -2711,18 +2711,23 @@ options_postprocess_verify_ce(const struct options *options, else { #ifdef ENABLE_CRYPTO_MBEDTLS - if (!(options->ca_file)) + if (!(options->ca_file || options->verify_hash_no_ca)) { - msg(M_USAGE, "You must define CA file (--ca)"); + msg(M_USAGE, "You must define CA file (--ca) and/or " + "peer fingeprint verification " + "(--peer-fingerprint)"); } if (options->ca_path) { msg(M_USAGE, "Parameter --capath cannot be used with the mbed TLS version version of OpenVPN."); } #else /* ifdef ENABLE_CRYPTO_MBEDTLS */ - if ((!(options->ca_file)) && (!(options->ca_path))) + if ((!(options->ca_file)) && (!(options->ca_path)) + && (!(options->verify_hash_no_ca))) { - msg(M_USAGE, "You must define CA file (--ca) or CA path (--capath)"); + msg(M_USAGE, "You must define CA file (--ca) or CA path " + "(--capath) and/or peer fingeprint verification " + "(--peer-fingerprint)"); } #endif if (pull) @@ -3205,6 +3210,13 @@ options_postprocess_mutate(struct options *o) options_postprocess_http_proxy_override(o); } #endif + if (!o->ca_file && !o->ca_path && o->verify_hash + && o->verify_hash_depth == 0) + { + msg(M_INFO, "Using certificate fingerprint to verify peer (no CA " + "option set). "); + o->verify_hash_no_ca = true; + } #if P2MP /* @@ -3440,8 +3452,11 @@ options_postprocess_filechecks(struct options *options) errs |= check_file_access_inline(options->dh_file_inline, CHKACC_FILE, options->dh_file, R_OK, "--dh"); - errs |= check_file_access_inline(options->ca_file_inline, CHKACC_FILE, - options->ca_file, R_OK, "--ca"); + if (!options->verify_hash_no_ca) + { + errs |= check_file_access_inline(options->ca_file_inline, CHKACC_FILE, + options->ca_file, R_OK, "--ca"); + } errs |= check_file_access_chroot(options->chroot_dir, CHKACC_FILE, options->ca_path, R_OK, "--capath"); diff --git a/src/openvpn/options.h b/src/openvpn/options.h index 30ec53d6..c68e89d2 100644 --- a/src/openvpn/options.h +++ b/src/openvpn/options.h @@ -561,6 +561,7 @@ struct options struct verify_hash_list *verify_hash; hash_algo_type verify_hash_algo; int verify_hash_depth; + bool verify_hash_no_ca; unsigned int ssl_flags; /* set to SSLF_x flags from ssl.h */ #ifdef ENABLE_PKCS11 diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h index 2b1b87fb..4e1ff6c8 100644 --- a/src/openvpn/ssl_common.h +++ b/src/openvpn/ssl_common.h @@ -285,6 +285,7 @@ struct tls_options const char *remote_cert_eku; struct verify_hash_list *verify_hash; int verify_hash_depth; + bool verify_hash_no_ca; hash_algo_type verify_hash_algo; #ifdef ENABLE_X509ALTUSERNAME char *x509_username_field[MAX_PARMS]; diff --git a/src/openvpn/ssl_verify_mbedtls.c b/src/openvpn/ssl_verify_mbedtls.c index 93891038..ef3847bb 100644 --- a/src/openvpn/ssl_verify_mbedtls.c +++ b/src/openvpn/ssl_verify_mbedtls.c @@ -62,6 +62,22 @@ verify_callback(void *session_obj, mbedtls_x509_crt *cert, int cert_depth, struct buffer cert_fingerprint = x509_get_sha256_fingerprint(cert, &gc); cert_hash_remember(session, cert_depth, &cert_fingerprint); + if (session->opt->verify_hash_no_ca) + { + /* + * If we decide to verify the peer certificate based on the fingerprint + * we ignore wrong dates and the certificate not being trusted. + * Any other problem with the certificate (wrong key, bad cert,...) + * will still trigger an error. + * Clearing these flags relies on verify_cert will later rejecting a + * certificate that has no matching fingerprint. + */ + uint32_t flags_ignore = MBEDTLS_X509_BADCERT_NOT_TRUSTED + | MBEDTLS_X509_BADCERT_EXPIRED + | MBEDTLS_X509_BADCERT_FUTURE; + *flags = *flags & ~flags_ignore; + } + /* did peer present cert which was signed by our root cert? */ if (*flags != 0) { diff --git a/src/openvpn/ssl_verify_openssl.c b/src/openvpn/ssl_verify_openssl.c index d063aeda..8b1f1969 100644 --- a/src/openvpn/ssl_verify_openssl.c +++ b/src/openvpn/ssl_verify_openssl.c @@ -67,7 +67,7 @@ verify_callback(int preverify_ok, X509_STORE_CTX *ctx) cert_hash_remember(session, X509_STORE_CTX_get_error_depth(ctx), &cert_hash); /* did peer present cert which was signed by our root cert? */ - if (!preverify_ok) + if (!preverify_ok && !session->opt->verify_hash_no_ca) { /* get the X509 name */ char *subject = x509_get_subject(current_cert, &gc);