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>
(cherry picked from commit aba758740d26224b7b3957df221def7ab80c5802)

diff --git a/Changes.rst b/Changes.rst
index 011fa2c0f6141883014abf2f949bea0fcc26ed38..21f066490d0315bfbe3a00ff46176ea1ae8d7288 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 2.4.4
 =============
 This is primarily a maintenance release, with further improved OpenSSL 1.1

diff --git a/doc/openvpn.8 b/doc/openvpn.8
index 0b3e1ad7087a8ec43235a4888c777c17171d7f15..e7242babd07a0bdeebe6155aae0d13f77afc0d56 100644 (file)
--- a/doc/openvpn.8
+++ b/doc/openvpn.8
@@ -4918,6 +4918,37 @@ 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 133a9f508425c0ad3aad06dd07d5c846860f84c1..04874b8ff4a4448fb198b9df3995f14ba1442880 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 5d3108afcce7fba529a01e109e81374603e4a3c9..7ede5273d1b0c5875581e4a5ac24435a975dec42 100644 (file)
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -600,6 +600,8 @@ 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"
@@ -874,6 +876,7 @@ init_options(struct options *o, const bool init_gc)
     o->renegotiate_seconds = 3600;
     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);
@@ -2745,6 +2749,7 @@ 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);
@@ -7852,6 +7857,11 @@ 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 01a7b267ca7a487fd1c4f2703d269d5aaf554559..28478f30d0e84f35051cc913f9118b2c3a6f6f6b 100644 (file)
--- a/src/openvpn/options.h
+++ b/src/openvpn/options.h
@@ -503,6 +503,7 @@ 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 0739cf7c1c7b24bdc819102bd814edc5471603ce..08e4b1215cce77ade6f7295b6d5eb302f7d23466 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 b2663099d0dac2332eded25ee71210b3b9152218..001a7865d1b076cc73b852754afb3c96d0d2e0ae 100644 (file)
--- a/src/openvpn/ssl_openssl.c
+++ b/src/openvpn/ssl_openssl.c
@@ -386,6 +386,40 @@ 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)
 {
@@ -1725,7 +1759,8 @@ 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;
@@ -1745,6 +1780,7 @@ 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");