Add --tls-cert-profile option.

This allows the user to specify what certificate crypto algorithms to
support.  The supported profiles are 'preferred', 'legacy' (default) and
'suiteb', as discussed in <84590a17-1c48-9df2-c48e-4160750b2e33@fox-it.com>
(https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14214.
html).

This fully implements the feature for mbed TLS builds, because for mbed it
is both more easy to implement and the most relevant because mbed TLS 2+
is by default somewhat restrictive by requiring 2048-bit+ for RSA keys.

For OpenSSL, this implements an approximation based on security levels, as
discussed at the hackathon in Karlsruhe.

This patch uses 'legacy' as the default profile following discussion on
the openvpn-devel mailing list.  This way this patch can be applied to
both the release/2.4 and master branches.  I'll send a follow-up patch for
the master branch to change the default to 'preferred' later.

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Antonio Quartulli <antonio@openvpn.net>
Message-Id: <20171112163636.17434-1-steffan@karger.me>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15848.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/Changes.rst b/Changes.rst
index db9b18b90db870d576c4d4cb86f8594a94cdd6ec..a6090cf5ebe78459ea608645f291120377b01bbe 100644 (file)
--- a/Changes.rst
+++ b/Changes.rst
@@ -321,6 +321,18 @@ Maintainer-visible changes
   i386/i686 builds on RHEL5.
 
 
+Version 2.4.5
+=============
+
+New features
+------------
+- The new option ``--tls-cert-profile`` can be used to restrict the set of
+  allowed crypto algorithms in TLS certificates in mbed TLS builds.  The
+  default profile is 'legacy' for now, which allows SHA1+, RSA-1024+ and any
+  elliptic curve certificates.  The default will be changed to the 'preferred'
+  profile in the future, which requires SHA2+, RSA-2048+ and any curve.
+
+
 Version 2.4.3
 =============
 

diff --git a/doc/openvpn.8 b/doc/openvpn.8
index eb5258f99953e736a9a1ee06537db691f7347c34..2b5cab12fd9df0a21fd4bb43eb7bc7be07ac6524 100644 (file)
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -4917,6 +4917,37 @@ when using mbed TLS or
 OpenSSL.
 .\"*********************************************************
 .TP
+.B \-\-tls\-cert\-profile profile
+Set the allowed cryptographic algorithms for certificates according to
+.B profile\fN.
+
+The following profiles are supported:
+
+.B legacy
+(default): SHA1 and newer, RSA 2048-bit+, any elliptic curve.
+
+.B preferred
+: SHA2 and newer, RSA 2048-bit+, any elliptic curve.
+
+.B suiteb
+: SHA256/SHA384, ECDSA with P-256 or P-384.
+
+This option is only fully supported for mbed TLS builds.  OpenSSL builds use
+the following approximation:
+
+.B legacy
+(default): sets "security level 1"
+
+.B preferred
+: sets "security level 2"
+
+.B suiteb
+: sets "security level 3" and \-\-tls\-cipher "SUITEB128".
+
+OpenVPN will migrate to 'preferred' as default in the future.  Please ensure
+that your keys already comply.
+.\"*********************************************************
+.TP
 .B \-\-tls\-timeout n
 Packet retransmit timeout on TLS control channel
 if no acknowledgment from remote within

diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index a4dd2c87641daa29638e72d99f8ded9125134526..408daf13f2f0327e45d3402e5bfa899256aac9fb 100644 (file)
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -1016,7 +1016,8 @@ print_openssl_info(const struct options *options)
         }
         if (options->show_tls_ciphers)
         {
-            show_available_tls_ciphers(options->cipher_list);
+            show_available_tls_ciphers(options->cipher_list,
+                                       options->tls_cert_profile);
         }
         if (options->show_curves)
         {

diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 0a5c6a64be4bb310245a21eb48d387b6429aaac3..8e5cdf7faf635ec95043fa7fec5d9086bdf5a28c 100644 (file)
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -599,6 +599,8 @@ static const char usage_message[] =
 #endif
     "--tls-cipher l  : A list l of allowable TLS ciphers separated by : (optional).\n"
     "                : Use --show-tls to see a list of supported TLS ciphers.\n"
+    "--tls-cert-profile p : Set the allowed certificate crypto algorithm profile\n"
+    "                  (default=legacy).\n"
     "--tls-timeout n : Packet retransmit timeout on TLS control channel\n"
     "                  if no ACK from remote within n seconds (default=%d).\n"
     "--reneg-bytes n : Renegotiate data chan. key after n bytes sent and recvd.\n"
@@ -875,6 +877,7 @@ init_options(struct options *o, const bool init_gc)
     o->renegotiate_seconds_min = -1;
     o->handshake_window = 60;
     o->transition_window = 3600;
+    o->tls_cert_profile = NULL;
     o->ecdh_curve = NULL;
 #ifdef ENABLE_X509ALTUSERNAME
     o->x509_username_field = X509_USERNAME_FIELD_DEFAULT;
@@ -1753,6 +1756,7 @@ show_settings(const struct options *o)
     SHOW_STR(cryptoapi_cert);
 #endif
     SHOW_STR(cipher_list);
+    SHOW_STR(tls_cert_profile);
     SHOW_STR(tls_verify);
     SHOW_STR(tls_export_cert);
     SHOW_INT(verify_x509_type);
@@ -2732,6 +2736,7 @@ options_postprocess_verify_ce(const struct options *options, const struct connec
         MUST_BE_UNDEF(pkcs12_file);
 #endif
         MUST_BE_UNDEF(cipher_list);
+        MUST_BE_UNDEF(tls_cert_profile);
         MUST_BE_UNDEF(tls_verify);
         MUST_BE_UNDEF(tls_export_cert);
         MUST_BE_UNDEF(verify_x509_name);
@@ -7834,6 +7839,11 @@ add_option(struct options *options,
         VERIFY_PERMISSION(OPT_P_GENERAL);
         options->cipher_list = p[1];
     }
+    else if (streq(p[0], "tls-cert-profile") && p[1] && !p[2])
+    {
+        VERIFY_PERMISSION(OPT_P_GENERAL);
+        options->tls_cert_profile = p[1];
+    }
     else if (streq(p[0], "crl-verify") && p[1] && ((p[2] && streq(p[2], "dir"))
                                                    || (p[2] && streq(p[1], INLINE_FILE_TAG) ) || !p[2]) && !p[3])
     {

diff --git a/src/openvpn/options.h b/src/openvpn/options.h
index a74dc94d0e0125311394cac1436db42fcca63803..035c6d158ef546f6e4508525135b39d596b97854 100644 (file)
--- a/src/openvpn/options.h
+++ b/src/openvpn/options.h
@@ -502,6 +502,7 @@ struct options
     const char *priv_key_file;
     const char *pkcs12_file;
     const char *cipher_list;
+    const char *tls_cert_profile;
     const char *ecdh_curve;
     const char *tls_verify;
     int verify_x509_type;

diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index 27f81cf30ba40f8b45279c25d88209caadeca966..843bc3934e13a1d1e16018b01853bb6b73e3ad73 100644 (file)
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -616,6 +616,9 @@ init_ssl(const struct options *options, struct tls_root_ctx *new_ctx)
         tls_ctx_client_new(new_ctx);
     }
 
+    /* Restrict allowed certificate crypto algorithms */
+    tls_ctx_set_cert_profile(new_ctx, options->tls_cert_profile);
+
     /* Allowable ciphers */
     /* Since @SECLEVEL also influces loading of certificates, set the
      * cipher restrictions before loading certificates */

diff --git a/src/openvpn/ssl_backend.h b/src/openvpn/ssl_backend.h
index aba5a4deec522cb6325ca5a19636047f29e98c92..f588110cf1827864a9106407b3b729f54faa8f2b 100644 (file)
--- a/src/openvpn/ssl_backend.h
+++ b/src/openvpn/ssl_backend.h
@@ -176,6 +176,16 @@ void tls_ctx_set_options(struct tls_root_ctx *ctx, unsigned int ssl_flags);
  */
 void tls_ctx_restrict_ciphers(struct tls_root_ctx *ctx, const char *ciphers);
 
+/**
+ * Set the TLS certificate profile.  The profile defines which crypto
+ * algorithms may be used in the supplied certificate.
+ *
+ * @param ctx           TLS context to restrict, must be valid.
+ * @param profile       The profile name ('preferred', 'legacy' or 'suiteb').
+ *                      Defaults to 'preferred' if NULL.
+ */
+void tls_ctx_set_cert_profile(struct tls_root_ctx *ctx, const char *profile);
+
 /**
  * Check our certificate notBefore and notAfter fields, and warn if the cert is
  * either not yet valid or has expired.  Note that this is a non-fatal error,
@@ -505,9 +515,12 @@ void print_details(struct key_state_ssl *ks_ssl, const char *prefix);
  * Show the TLS ciphers that are available for us to use in the OpenSSL
  * library.
  *
- * @param               - list of allowed TLS cipher, or NULL.
+ * @param cipher_list       list of allowed TLS cipher, or NULL.
+ * @param tls_cert_profile  TLS certificate crypto profile name.
  */
-void show_available_tls_ciphers(const char *tls_ciphers);
+void
+show_available_tls_ciphers(const char *cipher_list,
+                           const char *tls_cert_profile);
 
 /*
  * Show the available elliptic curves in the crypto library

diff --git a/src/openvpn/ssl_mbedtls.c b/src/openvpn/ssl_mbedtls.c
index 861d936dbd4277d1690124685da2b7505c64f54a..09829ebb5b2b2389e9030d4e9e3794a6a736e65f 100644 (file)
--- a/src/openvpn/ssl_mbedtls.c
+++ b/src/openvpn/ssl_mbedtls.c
@@ -62,6 +62,34 @@
 #include <mbedtls/pem.h>
 #include <mbedtls/sha256.h>
 
+static const mbedtls_x509_crt_profile openvpn_x509_crt_profile_legacy =
+{
+    /* Hashes from SHA-1 and above */
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA1 ) |
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_RIPEMD160 ) |
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA224 ) |
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA256 ) |
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA384 ) |
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA512 ),
+    0xFFFFFFF, /* Any PK alg    */
+    0xFFFFFFF, /* Any curve     */
+    1024,      /* RSA-1024 and larger */
+};
+
+static const mbedtls_x509_crt_profile openvpn_x509_crt_profile_preferred =
+{
+    /* SHA-2 and above */
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA224 ) |
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA256 ) |
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA384 ) |
+    MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA512 ),
+    0xFFFFFFF, /* Any PK alg    */
+    0xFFFFFFF, /* Any curve     */
+    2048,      /* RSA-2048 and larger */
+};
+
+#define openvpn_x509_crt_profile_suiteb mbedtls_x509_crt_profile_suiteb;
+
 void
 tls_init_lib(void)
 {
@@ -250,6 +278,27 @@ tls_ctx_restrict_ciphers(struct tls_root_ctx *ctx, const char *ciphers)
     free(tmp_ciphers_orig);
 }
 
+void
+tls_ctx_set_cert_profile(struct tls_root_ctx *ctx, const char *profile)
+{
+    if (!profile || 0 == strcmp(profile, "legacy"))
+    {
+        ctx->cert_profile = openvpn_x509_crt_profile_legacy;
+    }
+    else if (0 == strcmp(profile, "preferred"))
+    {
+        ctx->cert_profile = openvpn_x509_crt_profile_preferred;
+    }
+    else if (0 == strcmp(profile, "suiteb"))
+    {
+        ctx->cert_profile = openvpn_x509_crt_profile_suiteb;
+    }
+    else
+    {
+        msg (M_FATAL, "ERROR: Invalid cert profile: %s", profile);
+    }
+}
+
 void
 tls_ctx_check_cert_time(const struct tls_root_ctx *ctx)
 {
@@ -917,6 +966,8 @@ key_state_ssl_init(struct key_state_ssl *ks_ssl,
     mbedtls_ssl_conf_rng(&ks_ssl->ssl_config, mbedtls_ctr_drbg_random,
                          rand_ctx_get());
 
+    mbedtls_ssl_conf_cert_profile(&ks_ssl->ssl_config, &ssl_ctx->cert_profile);
+
     if (ssl_ctx->allowed_ciphers)
     {
         mbedtls_ssl_conf_ciphersuites(&ks_ssl->ssl_config, ssl_ctx->allowed_ciphers);
@@ -1271,12 +1322,14 @@ print_details(struct key_state_ssl *ks_ssl, const char *prefix)
 }
 
 void
-show_available_tls_ciphers(const char *cipher_list)
+show_available_tls_ciphers(const char *cipher_list,
+                           const char *tls_cert_profile)
 {
     struct tls_root_ctx tls_ctx;
     const int *ciphers = mbedtls_ssl_list_ciphersuites();
 
     tls_ctx_server_new(&tls_ctx);
+    tls_ctx_set_cert_profile(&tls_ctx, tls_cert_profile);
     tls_ctx_restrict_ciphers(&tls_ctx, cipher_list);
 
     if (tls_ctx.allowed_ciphers)

diff --git a/src/openvpn/ssl_mbedtls.h b/src/openvpn/ssl_mbedtls.h
index f69b61003c11d68a79bd38285197292c58a8f918..341da7d4c68fd4935d1f4a13352482c7a2a8cd06 100644 (file)
--- a/src/openvpn/ssl_mbedtls.h
+++ b/src/openvpn/ssl_mbedtls.h
@@ -82,6 +82,7 @@ struct tls_root_ctx {
     struct external_context *external_key; /**< Management external key */
 #endif
     int *allowed_ciphers;       /**< List of allowed ciphers for this connection */
+    mbedtls_x509_crt_profile cert_profile; /**< Allowed certificate types */
 };
 
 struct key_state_ssl {

diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c
index 0bfb693945bbdbfe7d28f03c98a828b7a803744a..de89cb13a6b68eaa0b439bec86d660c693f72a02 100644 (file)
--- a/src/openvpn/ssl_openssl.c
+++ b/src/openvpn/ssl_openssl.c
@@ -383,6 +383,40 @@ tls_ctx_restrict_ciphers(struct tls_root_ctx *ctx, const char *ciphers)
     }
 }
 
+void
+tls_ctx_set_cert_profile(struct tls_root_ctx *ctx, const char *profile)
+{
+#if (OPENSSL_VERSION_NUMBER >= 0x10100000)
+    /* OpenSSL does not have certificate profiles, but a complex set of
+     * callbacks that we could try to implement to achieve something similar.
+     * For now, use OpenSSL's security levels to achieve similar (but not equal)
+     * behaviour. */
+    if (!profile || 0 == strcmp(profile, "legacy"))
+    {
+        SSL_CTX_set_security_level(ctx->ctx, 1);
+    }
+    else if (0 == strcmp(profile, "preferred"))
+    {
+        SSL_CTX_set_security_level(ctx->ctx, 2);
+    }
+    else if (0 == strcmp(profile, "suiteb"))
+    {
+        SSL_CTX_set_security_level(ctx->ctx, 3);
+        SSL_CTX_set_cipher_list(ctx->ctx, "SUITEB128");
+    }
+    else
+    {
+        msg(M_FATAL, "ERROR: Invalid cert profile: %s", profile);
+    }
+#else
+    if (profile)
+    {
+        msg(M_WARN, "WARNING: OpenSSL 1.0.1 does not support --tls-cert-profile"
+            ", ignoring user-set profile: '%s'", profile);
+    }
+#endif
+}
+
 void
 tls_ctx_check_cert_time(const struct tls_root_ctx *ctx)
 {
@@ -1722,7 +1756,8 @@ print_details(struct key_state_ssl *ks_ssl, const char *prefix)
 }
 
 void
-show_available_tls_ciphers(const char *cipher_list)
+show_available_tls_ciphers(const char *cipher_list,
+                           const char *tls_cert_profile)
 {
     struct tls_root_ctx tls_ctx;
     SSL *ssl;
@@ -1742,6 +1777,7 @@ show_available_tls_ciphers(const char *cipher_list)
         crypto_msg(M_FATAL, "Cannot create SSL object");
     }
 
+    tls_ctx_set_cert_profile(&tls_ctx, tls_cert_profile);
     tls_ctx_restrict_ciphers(&tls_ctx, cipher_list);
 
     printf("Available TLS Ciphers,\n");