============ Make self-signed cert: $ openssl req -x509 -newkey ec:<(openssl ecparam -name secp384r1) -keyout key.pem -out cert.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 cert.pem -noout -sha256 -fingerprint | sed 's/.*=//;s/\(.*\)/\L\1/')" Start openvpn with tls verify script: $ sudo openvpn --server 10.66.0.0 255.255.255.0 --dev tun --dh none --ca none --cert cert.pem --key key.pem --tls-verify $(readlink -f tls-verify.sh) --script-security 2 TLS Verify Script: ================== #!/bin/sh [ -n "$tls_digest_sha256_0" -a -e "/tmp/allowed-openvpn-fingerprints/$tls_digest_sha256_0" ] Client side: ============ Make self-signed cert: $ openssl req -x509 -newkey ec:<(openssl ecparam -name secp384r1) -keyout key.pem -out cert.pem -nodes -sha256 -days 3650 -subj '/CN=client' "Tell" the server about our fingerprint: $ mkdir -p /tmp/allowed-openvpn-fingerprints; touch "/tmp/allowed-openvpn-fingerprints/$(openssl x509 -in cert.pem -noout -sha256 -fingerprint | sed 's/.*=//;s/\(.*\)/\L\1/')" Start openvpn with server fingerprint verification: $ sudo openvpn --client --remote 127.0.0.1 --dev tun --ca none --cert cert.pem --key key.pem --verify-hash "$server_fingerprint" SHA256 --nobind Signed-off-by: Jason A. Donenfeld --- Sorry for the double post. Somebody suggested I submit this as an actual git patch instead of as just part of the goofy email I sent earlier. So here's that email turned into a proper patch that you can apply. Feel free to hack the patch to pieces or discard it and start over. src/openvpn/init.c | 1 + src/openvpn/options.c | 9 ++++++++- src/openvpn/options.h | 1 + src/openvpn/ssl.c | 2 +- src/openvpn/ssl_common.h | 1 + src/openvpn/ssl_verify.c | 2 +- src/openvpn/ssl_verify_mbedtls.c | 2 +- src/openvpn/ssl_verify_openssl.c | 2 +- 8 files changed, 15 insertions(+), 5 deletions(-) diff --git a/src/openvpn/init.c b/src/openvpn/init.c index 36c1a4c4..4da994d8 100644 --- a/src/openvpn/init.c +++ b/src/openvpn/init.c @@ -2722,6 +2722,7 @@ do_init_crypto_tls(struct context *c, const unsigned int flags) to.remote_cert_eku = options->remote_cert_eku; to.verify_hash = options->verify_hash; to.verify_hash_algo = options->verify_hash_algo; + to.ca_file_none = options->ca_file_none; #ifdef ENABLE_X509ALTUSERNAME to.x509_username_field = (char *) options->x509_username_field; #else diff --git a/src/openvpn/options.c b/src/openvpn/options.c index 426057ab..dad706d9 100644 --- a/src/openvpn/options.c +++ b/src/openvpn/options.c @@ -3259,7 +3259,10 @@ options_postprocess_filechecks(struct options *options) /* ** SSL/TLS/crypto related files ** */ errs |= check_file_access(CHKACC_FILE|CHKACC_INLINE, options->dh_file, R_OK, "--dh"); - errs |= check_file_access(CHKACC_FILE|CHKACC_INLINE, options->ca_file, R_OK, "--ca"); + if (!options->ca_file_none) + { + errs |= check_file_access(CHKACC_FILE|CHKACC_INLINE, options->ca_file, R_OK, "--ca"); + } errs |= check_file_access_chroot(options->chroot_dir, CHKACC_FILE, options->ca_path, R_OK, "--capath"); errs |= check_file_access(CHKACC_FILE|CHKACC_INLINE, options->cert_file, R_OK, "--cert"); errs |= check_file_access(CHKACC_FILE|CHKACC_INLINE, options->extra_certs_file, R_OK, @@ -7638,6 +7641,10 @@ add_option(struct options *options, { options->ca_file_inline = p[2]; } + else if (streq(p[1], "none")) + { + options->ca_file_none = true; + } } #ifndef ENABLE_CRYPTO_MBEDTLS else if (streq(p[0], "capath") && p[1] && !p[2]) diff --git a/src/openvpn/options.h b/src/openvpn/options.h index f7d0145a..6ccdca49 100644 --- a/src/openvpn/options.h +++ b/src/openvpn/options.h @@ -489,6 +489,7 @@ struct options /* TLS (control channel) parms */ bool tls_server; bool tls_client; + bool ca_file_none; const char *ca_file; const char *ca_path; const char *dh_file; diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c index 669f941b..0ef0f31f 100644 --- a/src/openvpn/ssl.c +++ b/src/openvpn/ssl.c @@ -693,7 +693,7 @@ init_ssl(const struct options *options, struct tls_root_ctx *new_ctx) } } - if (options->ca_file || options->ca_path) + if ((!options->ca_file_none && options->ca_file) || options->ca_path) { tls_ctx_load_ca(new_ctx, options->ca_file, options->ca_file_inline, options->ca_path, options->tls_server); diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h index 08ef6ffa..e9ac5271 100644 --- a/src/openvpn/ssl_common.h +++ b/src/openvpn/ssl_common.h @@ -270,6 +270,7 @@ struct tls_options uint8_t *verify_hash; hash_algo_type verify_hash_algo; char *x509_username_field; + bool ca_file_none; /* allow openvpn config info to be * passed over control channel */ diff --git a/src/openvpn/ssl_verify.c b/src/openvpn/ssl_verify.c index 25395b27..61873e6f 100644 --- a/src/openvpn/ssl_verify.c +++ b/src/openvpn/ssl_verify.c @@ -720,7 +720,7 @@ verify_cert(struct tls_session *session, openvpn_x509_cert_t *cert, int cert_dep } /* verify level 1 cert, i.e. the CA that signed our leaf cert */ - if (cert_depth == 1 && opt->verify_hash) + if ((opt->ca_file_none || cert_depth == 1) && opt->verify_hash) { struct buffer ca_hash = {0}; diff --git a/src/openvpn/ssl_verify_mbedtls.c b/src/openvpn/ssl_verify_mbedtls.c index fd31bbbd..147fb983 100644 --- a/src/openvpn/ssl_verify_mbedtls.c +++ b/src/openvpn/ssl_verify_mbedtls.c @@ -63,7 +63,7 @@ verify_callback(void *session_obj, mbedtls_x509_crt *cert, int cert_depth, cert_hash_remember(session, cert_depth, &cert_fingerprint); /* did peer present cert which was signed by our root cert? */ - if (*flags != 0) + if (*flags != 0 && !session->opt->ca_file_none) { int ret = 0; char errstr[512] = { 0 }; diff --git a/src/openvpn/ssl_verify_openssl.c b/src/openvpn/ssl_verify_openssl.c index 9b984751..10d351f4 100644 --- a/src/openvpn/ssl_verify_openssl.c +++ b/src/openvpn/ssl_verify_openssl.c @@ -66,7 +66,7 @@ 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->ca_file_none) { /* get the X509 name */ char *subject = x509_get_subject(current_cert, &gc);