TLS v1.2 support for cryptoapicert -- RSA only

- If an NCRYPT handle for the private key can be obtained, use
  NCryptSignHash from the Cryptography NG API to sign the hash.

  This should work for all keys in the Windows certifiate stores
  but may fail for keys in a legacy token, for example. In such
  cases, we disable TLS v1.2 and fall back to the current
  behaviour. A warning is logged unless TLS version is already
  restricted to <= 1.1

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1516423974-22159-1-git-send-email-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16288.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 51d57d7dad6c6380df7b76bbec1897ea4f98474d)

diff --git a/src/openvpn/Makefile.am b/src/openvpn/Makefile.am
index fcc22d684f90879a4061a721a64ed2305531c9ad..1a2f42e1d676674fcc154b2d2947d9649295fef7 100644 (file)
--- a/src/openvpn/Makefile.am
+++ b/src/openvpn/Makefile.am
@@ -132,5 +132,5 @@ openvpn_LDADD = \
        $(OPTIONAL_DL_LIBS)
 if WIN32
 openvpn_SOURCES += openvpn_win32_resources.rc block_dns.c block_dns.h
-openvpn_LDADD += -lgdi32 -lws2_32 -lwininet -lcrypt32 -liphlpapi -lwinmm -lfwpuclnt -lrpcrt4
+openvpn_LDADD += -lgdi32 -lws2_32 -lwininet -lcrypt32 -liphlpapi -lwinmm -lfwpuclnt -lrpcrt4 -lncrypt
 endif

diff --git a/src/openvpn/cryptoapi.c b/src/openvpn/cryptoapi.c
index 4f2c636b0aaed6e84bd7f7fb18d27dcf94f0a2e4..f155123d0bdb87d74401f73439f853af902cbaeb 100644 (file)
--- a/src/openvpn/cryptoapi.c
+++ b/src/openvpn/cryptoapi.c
@@ -42,6 +42,7 @@
 #include <openssl/err.h>
 #include <windows.h>
 #include <wincrypt.h>
+#include <ncrypt.h>
 #include <stdio.h>
 #include <ctype.h>
 #include <assert.h>
@@ -83,6 +84,7 @@
 #define CRYPTOAPI_F_CRYPT_SIGN_HASH                         106
 #define CRYPTOAPI_F_LOAD_LIBRARY                            107
 #define CRYPTOAPI_F_GET_PROC_ADDRESS                        108
+#define CRYPTOAPI_F_NCRYPT_SIGN_HASH                        109
 
 static ERR_STRING_DATA CRYPTOAPI_str_functs[] = {
     { ERR_PACK(ERR_LIB_CRYPTOAPI, 0, 0),                                    "microsoft cryptoapi"},
@@ -95,12 +97,13 @@ static ERR_STRING_DATA CRYPTOAPI_str_functs[] = {
     { ERR_PACK(0, CRYPTOAPI_F_CRYPT_SIGN_HASH, 0),                          "CryptSignHash" },
     { ERR_PACK(0, CRYPTOAPI_F_LOAD_LIBRARY, 0),                             "LoadLibrary" },
     { ERR_PACK(0, CRYPTOAPI_F_GET_PROC_ADDRESS, 0),                         "GetProcAddress" },
+    { ERR_PACK(0, CRYPTOAPI_F_NCRYPT_SIGN_HASH, 0),                         "NCryptSignHash" },
     { 0, NULL }
 };
 
 typedef struct _CAPI_DATA {
     const CERT_CONTEXT *cert_context;
-    HCRYPTPROV crypt_prov;
+    HCRYPTPROV_OR_NCRYPT_KEY_HANDLE crypt_prov;
     DWORD key_spec;
     BOOL free_crypt_prov;
 } CAPI_DATA;
@@ -210,6 +213,41 @@ rsa_pub_dec(int flen, const unsigned char *from, unsigned char *to, RSA *rsa, in
     return 0;
 }
 
+/**
+ * Sign the hash in 'from' using NCryptSignHash(). This requires an NCRYPT
+ * key handle in cd->crypt_prov. On return the signature is in 'to'. Returns
+ * the length of the signature or 0 on error.
+ * For now we support only RSA and the padding is assumed to be PKCS1 v1.5
+ */
+static int
+priv_enc_CNG(const CAPI_DATA *cd, const unsigned char *from, int flen,
+              unsigned char *to, int tlen, int padding)
+{
+    NCRYPT_KEY_HANDLE hkey = cd->crypt_prov;
+    DWORD len;
+    ASSERT(cd->key_spec == CERT_NCRYPT_KEY_SPEC);
+
+    msg(D_LOW, "Signing hash using CNG: data size = %d", flen);
+
+    /* The hash OID is already in 'from'.  So set the hash algorithm
+     * in the padding info struct to NULL.
+     */
+    BCRYPT_PKCS1_PADDING_INFO padinfo = {NULL};
+    DWORD status;
+
+    status = NCryptSignHash(hkey, padding? &padinfo : NULL, (BYTE*) from, flen,
+                            to, tlen, &len, padding? BCRYPT_PAD_PKCS1 : 0);
+    if (status != ERROR_SUCCESS)
+    {
+        SetLastError(status);
+        CRYPTOAPIerr(CRYPTOAPI_F_NCRYPT_SIGN_HASH);
+        len = 0;
+    }
+
+    /* Unlike CAPI, CNG signature is in big endian order. No reversing needed. */
+    return len;
+}
+
 /* sign arbitrary data */
 static int
 rsa_priv_enc(int flen, const unsigned char *from, unsigned char *to, RSA *rsa, int padding)
@@ -230,6 +268,11 @@ rsa_priv_enc(int flen, const unsigned char *from, unsigned char *to, RSA *rsa, i
         RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
         return 0;
     }
+    if (cd->key_spec == CERT_NCRYPT_KEY_SPEC)
+    {
+        return priv_enc_CNG(cd, from, flen, to, RSA_size(rsa), padding);
+    }
+
     /* Unfortunately, there is no "CryptSign()" function in CryptoAPI, that would
      * be way to straightforward for M$, I guess... So we have to do it this
      * tricky way instead, by creating a "Hash", and load the already-made hash
@@ -322,7 +365,14 @@ finish(RSA *rsa)
     }
     if (cd->crypt_prov && cd->free_crypt_prov)
     {
-        CryptReleaseContext(cd->crypt_prov, 0);
+        if (cd->key_spec == CERT_NCRYPT_KEY_SPEC)
+        {
+            NCryptFreeObject(cd->crypt_prov);
+        }
+        else
+        {
+            CryptReleaseContext(cd->crypt_prov, 0);
+        }
     }
     if (cd->cert_context)
     {
@@ -458,8 +508,11 @@ SSL_CTX_use_CryptoAPI_certificate(SSL_CTX *ssl_ctx, const char *cert_prop)
     }
 
     /* set up stuff to use the private key */
-    if (!CryptAcquireCertificatePrivateKey(cd->cert_context, CRYPT_ACQUIRE_COMPARE_KEY_FLAG,
-                                           NULL, &cd->crypt_prov, &cd->key_spec, &cd->free_crypt_prov))
+    /* We prefer to get an NCRYPT key handle so that TLS1.2 can be supported */
+    DWORD flags = CRYPT_ACQUIRE_COMPARE_KEY_FLAG
+                  | CRYPT_ACQUIRE_PREFER_NCRYPT_KEY_FLAG;
+    if (!CryptAcquireCertificatePrivateKey(cd->cert_context, flags, NULL,
+                    &cd->crypt_prov, &cd->key_spec, &cd->free_crypt_prov))
     {
         /* if we don't have a smart card reader here, and we try to access a
          * smart card certificate, we get:
@@ -470,6 +523,21 @@ SSL_CTX_use_CryptoAPI_certificate(SSL_CTX *ssl_ctx, const char *cert_prop)
     /* here we don't need to do CryptGetUserKey() or anything; all necessary key
      * info is in cd->cert_context, and then, in cd->crypt_prov.  */
 
+    /* if we do not have an NCRYPT key handle restrict TLS to v1.1 or lower */
+    int max_version = SSL_CTX_get_max_proto_version(ssl_ctx);
+    if ((!max_version || max_version > TLS1_1_VERSION)
+        && cd->key_spec != CERT_NCRYPT_KEY_SPEC)
+    {
+        msg(M_WARN,"WARNING: cryptoapicert: private key is in a legacy store."
+            " Restricting TLS version to 1.1");
+        if (!SSL_CTX_set_max_proto_version(ssl_ctx, TLS1_1_VERSION))
+        {
+            msg(M_NONFATAL,"ERROR: cryptoapicert: unable to set max TLS version"
+                " to 1.1. Try config option --tls-version-min 1.1");
+            goto err;
+        }
+    }
+
     my_rsa_method = RSA_meth_new("Microsoft Cryptography API RSA Method",
                                   RSA_METHOD_FLAG_NO_CHECK);
     check_malloc_return(my_rsa_method);
@@ -550,7 +618,14 @@ err:
         {
             if (cd->free_crypt_prov && cd->crypt_prov)
             {
-                CryptReleaseContext(cd->crypt_prov, 0);
+                if (cd->key_spec == CERT_NCRYPT_KEY_SPEC)
+                {
+                    NCryptFreeObject(cd->crypt_prov);
+                }
+                else
+                {
+                    CryptReleaseContext(cd->crypt_prov, 0);
+                }
             }
             if (cd->cert_context)
             {

diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index f72e08ce77fefe42db689473f81b1535adae9e52..80cd648a368f1eff5c84e001ffb32dd916d91f8d 100644 (file)
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -3057,24 +3057,6 @@ options_postprocess_mutate(struct options *o)
     }
 #endif
 
-#ifdef ENABLE_CRYPTOAPI
-    if (o->cryptoapi_cert)
-    {
-        const int tls_version_max =
-            (o->ssl_flags >> SSLF_TLS_VERSION_MAX_SHIFT)
-            &SSLF_TLS_VERSION_MAX_MASK;
-
-        if (tls_version_max == TLS_VER_UNSPEC || tls_version_max > TLS_VER_1_1)
-        {
-            msg(M_WARN, "Warning: cryptapicert used, setting maximum TLS "
-                "version to 1.1.");
-            o->ssl_flags &= ~(SSLF_TLS_VERSION_MAX_MASK
-                              <<SSLF_TLS_VERSION_MAX_SHIFT);
-            o->ssl_flags |= (TLS_VER_1_1 << SSLF_TLS_VERSION_MAX_SHIFT);
-        }
-    }
-#endif /* ENABLE_CRYPTOAPI */
-
 #if P2MP
     /*
      * Save certain parms before modifying options via --pull