[Openvpn-devel,5/5] Prefer TLS libraries TLS PRF function, fix OpenVPN in FIPS mode

Message ID 20200907162221.20928-3-arne@rfc2549.org
State New
Headers show
Series
  • Untitled series #902
Related show

Commit Message

Arne Schwabe Sept. 7, 2020, 4:22 p.m.
This moves from using our own copy of the TLS1 PRF function to using
TLS library provided function where possible. This includes currently
OpenSSL 1.1.0+ and mbed TLS 2.18+.

For the libraries where it is not possible to use the library's own
function, we still use our own implementation. mbed TLS will continue
to use our own old PRF function while for OpenSSL we will use a
adapted version from OpenSSL 1.0.2t code. The version allows to be
used in a FIPS enabled environment.

The old OpenSSL and mbed TLS implementation could have shared some
more code but as we will eventually drop support for older TLS
libraries, the separation makes it easier it remove that code
invdidually.

No FIPS conformitiy testing etc has been done, this is only about
allowing OpenVPN on a system where FIPS mode has been enabled system
wide (e.g. on RHEL derivates).

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
---
 src/openvpn/crypto_backend.h           |  19 +++
 src/openvpn/crypto_mbedtls.c           | 143 ++++++++++++++++++++
 src/openvpn/crypto_openssl.c           | 172 ++++++++++++++++++++++++-
 src/openvpn/ssl.c                      | 130 +------------------
 tests/unit_tests/openvpn/test_crypto.c |  32 +++++
 5 files changed, 366 insertions(+), 130 deletions(-)

Patch

diff --git a/src/openvpn/crypto_backend.h b/src/openvpn/crypto_backend.h
index 85cb084a..b72684ce 100644
--- a/src/openvpn/crypto_backend.h
+++ b/src/openvpn/crypto_backend.h
@@ -699,4 +699,23 @@  const char *translate_cipher_name_from_openvpn(const char *cipher_name);
  */
 const char *translate_cipher_name_to_openvpn(const char *cipher_name);
 
+
+/**
+ * Calculates the TLS 1.0-1.1 PRF function. For the exact specification of the
+ * fun ction definition see the TLS RFCs like RFC 4346.
+ *
+ * @param seed          seed to use
+ * @param seed_len      length of the seed
+ * @param secret        secret to use
+ * @param secret_len    length of the secret
+ * @param output        output destination
+ * @param output_len    length of output/number of bytes to generate
+ */
+void
+ssl_tls1_PRF(const uint8_t *seed,
+             int seed_len,
+             const uint8_t *secret,
+             int secret_len,
+             uint8_t *output,
+             int output_len);
 #endif /* CRYPTO_BACKEND_H_ */
diff --git a/src/openvpn/crypto_mbedtls.c b/src/openvpn/crypto_mbedtls.c
index fbb1f120..dcdd964a 100644
--- a/src/openvpn/crypto_mbedtls.c
+++ b/src/openvpn/crypto_mbedtls.c
@@ -54,6 +54,7 @@ 
 #include <mbedtls/pem.h>
 
 #include <mbedtls/entropy.h>
+#include <mbedtls/ssl.h>
 
 
 /*
@@ -984,4 +985,146 @@  memcmp_constant_time(const void *a, const void *b, size_t size)
 
     return diff;
 }
+/* mbedtls-2.18.0 or newer */
+#ifdef HAVE_MBEDTLS_SSL_TLS_PRF
+void
+ssl_tls1_PRF(const uint8_t *seed,
+            int seed_len,
+            const uint8_t *secret,
+            int secret_len,
+            uint8_t *output,
+            int output_len)
+{
+    mbedtls_ssl_tls_prf(MBEDTLS_SSL_TLS_PRF_TLS1, secret, secret_len, "", seed,
+                        seed_len, output, output_len);
+}
+#else
+/*
+ * Generate the hash required by for the \c tls1_PRF function.
+ *
+ * @param md_kt         Message digest to use
+ * @param sec           Secret to base the hash on
+ * @param sec_len       Length of the secret
+ * @param seed          Seed to hash
+ * @param seed_len      Length of the seed
+ * @param out           Output buffer
+ * @param olen          Length of the output buffer
+ */
+static void
+tls1_P_hash(const md_kt_t *md_kt,
+            const uint8_t *sec,
+            int sec_len,
+            const uint8_t *seed,
+            int seed_len,
+            uint8_t *out,
+            int olen)
+{
+    struct gc_arena gc = gc_new();
+    uint8_t A1[MAX_HMAC_KEY_LENGTH];
+
+#ifdef ENABLE_DEBUG
+    const int olen_orig = olen;
+    const uint8_t *out_orig = out;
+#endif
+
+    hmac_ctx_t *ctx = hmac_ctx_new();
+    hmac_ctx_t *ctx_tmp = hmac_ctx_new();
+
+    dmsg(D_SHOW_KEY_SOURCE, "tls1_P_hash sec: %s", format_hex(sec, sec_len, 0, &gc));
+    dmsg(D_SHOW_KEY_SOURCE, "tls1_P_hash seed: %s", format_hex(seed, seed_len, 0, &gc));
+
+    int chunk = md_kt_size(md_kt);
+    unsigned int A1_len = md_kt_size(md_kt);
+
+    hmac_ctx_init(ctx, sec, sec_len, md_kt);
+    hmac_ctx_init(ctx_tmp, sec, sec_len, md_kt);
+
+    hmac_ctx_update(ctx,seed,seed_len);
+    hmac_ctx_final(ctx, A1);
+
+    for (;; )
+    {
+        hmac_ctx_reset(ctx);
+        hmac_ctx_reset(ctx_tmp);
+        hmac_ctx_update(ctx,A1,A1_len);
+        hmac_ctx_update(ctx_tmp,A1,A1_len);
+        hmac_ctx_update(ctx,seed,seed_len);
+
+        if (olen > chunk)
+        {
+            hmac_ctx_final(ctx, out);
+            out += chunk;
+            olen -= chunk;
+            hmac_ctx_final(ctx_tmp, A1); /* calc the next A1 value */
+        }
+        else    /* last one */
+        {
+            hmac_ctx_final(ctx, A1);
+            memcpy(out,A1,olen);
+            break;
+        }
+    }
+    hmac_ctx_cleanup(ctx);
+    hmac_ctx_free(ctx);
+    hmac_ctx_cleanup(ctx_tmp);
+    hmac_ctx_free(ctx_tmp);
+    secure_memzero(A1, sizeof(A1));
+
+    dmsg(D_SHOW_KEY_SOURCE, "tls1_P_hash out: %s", format_hex(out_orig, olen_orig, 0, &gc));
+    gc_free(&gc);
+}
+
+/*
+ * Use the TLS PRF function for generating data channel keys.
+ * This code is based on the OpenSSL library.
+ *
+ * TLS generates keys as such:
+ *
+ * master_secret[48] = PRF(pre_master_secret[48], "master secret",
+ *                         ClientHello.random[32] + ServerHello.random[32])
+ *
+ * key_block[] = PRF(SecurityParameters.master_secret[48],
+ *                 "key expansion",
+ *                 SecurityParameters.server_random[32] +
+ *                 SecurityParameters.client_random[32]);
+ *
+ * Notes:
+ *
+ * (1) key_block contains a full set of 4 keys.
+ * (2) The pre-master secret is generated by the client.
+ */
+void
+ssl_tls1_PRF(const uint8_t *label,
+         int label_len,
+         const uint8_t *sec,
+         int slen,
+         uint8_t *out1,
+         int olen)
+{
+    struct gc_arena gc = gc_new();
+    const md_kt_t *md5 = md_kt_get("MD5");
+    const md_kt_t *sha1 = md_kt_get("SHA1");
+
+    uint8_t *out2 = (uint8_t *) gc_malloc(olen, false, &gc);
+
+    int len = slen/2;
+    const uint8_t *S1 = sec;
+    const uint8_t *S2 = &(sec[len]);
+    len += (slen&1); /* add for odd, make longer */
+
+    tls1_P_hash(md5,S1,len,label,label_len,out1,olen);
+    tls1_P_hash(sha1,S2,len,label,label_len,out2,olen);
+
+    for (int i = 0; i<olen; i++)
+    {
+        out1[i] ^= out2[i];
+    }
+
+    secure_memzero(out2, olen);
+
+    dmsg(D_SHOW_KEY_SOURCE, "tls1_PRF out[%d]: %s", olen, format_hex(out1, olen, 0, &gc));
+
+    gc_free(&gc);
+}
+#endif
 #endif /* ENABLE_CRYPTO_MBEDTLS */
diff --git a/src/openvpn/crypto_openssl.c b/src/openvpn/crypto_openssl.c
index 75557cca..8ebc52e7 100644
--- a/src/openvpn/crypto_openssl.c
+++ b/src/openvpn/crypto_openssl.c
@@ -50,7 +50,9 @@ 
 #include <openssl/objects.h>
 #include <openssl/rand.h>
 #include <openssl/ssl.h>
-
+#if OPENSSL_VERSION_NUMBER >= 0x10100000L
+#include <openssl/kdf.h>
+#endif
 /*
  * Check for key size creepage.
  */
@@ -1121,4 +1123,172 @@  engine_load_key(const char *file, SSL_CTX *ctx)
 #endif /* if HAVE_OPENSSL_ENGINE */
 }
 
+#if OPENSSL_VERSION_NUMBER >= 0x10100000L
+void
+ssl_tls1_PRF(const uint8_t *seed,
+             int seed_len,
+             const uint8_t *secret,
+             int secret_len,
+             uint8_t *output,
+             int output_len)
+{
+    EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL);
+    ASSERT(EVP_PKEY_derive_init(pctx) == 1);
+
+    ASSERT(EVP_PKEY_CTX_set_tls1_prf_md(pctx, EVP_md5_sha1()) == 1);
+
+    ASSERT(EVP_PKEY_CTX_set1_tls1_prf_secret(pctx, secret, secret_len) == 1);
+
+    ASSERT(EVP_PKEY_CTX_add1_tls1_prf_seed(pctx, seed, seed_len) == 1);
+
+    size_t out_len = output_len;
+    ASSERT (EVP_PKEY_derive(pctx, output, &out_len) == 1);
+    ASSERT (out_len == output_len);
+}
+#else
+/*
+ * Generate the hash required by for the \c tls1_PRF function.
+ *
+ * We cannot use our normal hmac_* function as they do not work
+ * in a FIPS environment and need to use the EVP_MD_* API, which
+ *
+ * The function below is adapted from OpenSSL 1.0.2t
+ *
+ * @param md_kt         Message digest to use
+ * @param sec           Secret to base the hash on
+ * @param sec_len       Length of the secret
+ * @param seed          Seed to hash
+ * @param seed_len      Length of the seed
+ * @param out           Output buffer
+ * @param olen          Length of the output buffer
+ */
+static
+int tls1_P_hash(const EVP_MD *md, const unsigned char *sec,
+                int sec_len,
+                const void *seed, int seed_len,
+                unsigned char *out, int olen)
+{
+    int chunk;
+    size_t j;
+    EVP_MD_CTX ctx, ctx_tmp, ctx_init;
+    EVP_PKEY *mac_key;
+    unsigned char A1[EVP_MAX_MD_SIZE];
+    size_t A1_len;
+    int ret = 0;
+
+    chunk = EVP_MD_size(md);
+    OPENSSL_assert(chunk >= 0);
+
+    EVP_MD_CTX_init(&ctx);
+    EVP_MD_CTX_init(&ctx_tmp);
+    EVP_MD_CTX_init(&ctx_init);
+    EVP_MD_CTX_set_flags(&ctx_init, EVP_MD_CTX_FLAG_NON_FIPS_ALLOW);
+    mac_key = EVP_PKEY_new_mac_key(EVP_PKEY_HMAC, NULL, sec, sec_len);
+    if (!mac_key)
+        goto err;
+    if (!EVP_DigestSignInit(&ctx_init, NULL, md, NULL, mac_key))
+        goto err;
+    if (!EVP_MD_CTX_copy_ex(&ctx, &ctx_init))
+        goto err;
+    if (!EVP_DigestSignUpdate(&ctx, seed, seed_len))
+        goto err;
+    if (!EVP_DigestSignFinal(&ctx, A1, &A1_len))
+        goto err;
+
+    for (;;) {
+        /* Reinit mac contexts */
+        if (!EVP_MD_CTX_copy_ex(&ctx, &ctx_init))
+            goto err;
+        if (!EVP_DigestSignUpdate(&ctx, A1, A1_len))
+            goto err;
+        if (olen > chunk && !EVP_MD_CTX_copy_ex(&ctx_tmp, &ctx))
+            goto err;
+        if (!EVP_DigestSignUpdate(&ctx, seed, seed_len))
+            goto err;
+
+        if (olen > chunk)
+        {
+            if (!EVP_DigestSignFinal(&ctx, out, &j))
+                goto err;
+            out += j;
+            olen -= j;
+            /* calc the next A1 value */
+            if (!EVP_DigestSignFinal(&ctx_tmp, A1, &A1_len))
+                goto err;
+        }
+        else
+        {
+            /* last one */
+
+            if (!EVP_DigestSignFinal(&ctx, A1, &A1_len))
+                goto err;
+            memcpy(out, A1, olen);
+            break;
+        }
+    }
+    ret = 1;
+err:
+    EVP_PKEY_free(mac_key);
+    EVP_MD_CTX_cleanup(&ctx);
+    EVP_MD_CTX_cleanup(&ctx_tmp);
+    EVP_MD_CTX_cleanup(&ctx_init);
+    OPENSSL_cleanse(A1, sizeof(A1));
+    return ret;
+}
+
+
+/*
+ * Use the TLS PRF function for generating data channel keys.
+ * This code is based on the OpenSSL library.
+ *
+ * TLS generates keys as such:
+ *
+ * master_secret[48] = PRF(pre_master_secret[48], "master secret",
+ *                         ClientHello.random[32] + ServerHello.random[32])
+ *
+ * key_block[] = PRF(SecurityParameters.master_secret[48],
+ *                 "key expansion",
+ *                 SecurityParameters.server_random[32] +
+ *                 SecurityParameters.client_random[32]);
+ *
+ * Notes:
+ *
+ * (1) key_block contains a full set of 4 keys.
+ * (2) The pre-master secret is generated by the client.
+ */
+void
+ssl_tls1_PRF(const uint8_t *label,
+         int label_len,
+         const uint8_t *sec,
+         int slen,
+         uint8_t *out1,
+         int olen)
+{
+    struct gc_arena gc = gc_new();
+    /* For some reason our md_kt_get("MD5") fails otherwise in the unit test */
+    const md_kt_t *md5 = EVP_md5();
+    const md_kt_t *sha1 = EVP_sha1();
+
+    uint8_t *out2 = (uint8_t *) gc_malloc(olen, false, &gc);
+
+    int len = slen/2;
+    const uint8_t *S1 = sec;
+    const uint8_t *S2 = &(sec[len]);
+    len += (slen&1); /* add for odd, make longer */
+
+    ASSERT(tls1_P_hash(md5,S1,len,label,label_len,out1,olen));
+    ASSERT(tls1_P_hash(sha1,S2,len,label,label_len,out2,olen));
+
+    for (int i = 0; i<olen; i++)
+    {
+        out1[i] ^= out2[i];
+    }
+
+    secure_memzero(out2, olen);
+
+    dmsg(D_SHOW_KEY_SOURCE, "tls1_PRF out[%d]: %s", olen, format_hex(out1, olen, 0, &gc));
+
+    gc_free(&gc);
+}
+#endif
 #endif /* ENABLE_CRYPTO_OPENSSL */
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index d8f2cf0d..fa1de5c1 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -1595,134 +1595,6 @@  key_source2_print(const struct key_source2 *k)
     key_source_print(&k->server, "Server");
 }
 
-/*
- * Generate the hash required by for the \c tls1_PRF function.
- *
- * @param md_kt         Message digest to use
- * @param sec           Secret to base the hash on
- * @param sec_len       Length of the secret
- * @param seed          Seed to hash
- * @param seed_len      Length of the seed
- * @param out           Output buffer
- * @param olen          Length of the output buffer
- */
-static void
-tls1_P_hash(const md_kt_t *md_kt,
-            const uint8_t *sec,
-            int sec_len,
-            const uint8_t *seed,
-            int seed_len,
-            uint8_t *out,
-            int olen)
-{
-    struct gc_arena gc = gc_new();
-    uint8_t A1[MAX_HMAC_KEY_LENGTH];
-
-#ifdef ENABLE_DEBUG
-    const int olen_orig = olen;
-    const uint8_t *out_orig = out;
-#endif
-
-    hmac_ctx_t *ctx = hmac_ctx_new();
-    hmac_ctx_t *ctx_tmp = hmac_ctx_new();
-
-    dmsg(D_SHOW_KEY_SOURCE, "tls1_P_hash sec: %s", format_hex(sec, sec_len, 0, &gc));
-    dmsg(D_SHOW_KEY_SOURCE, "tls1_P_hash seed: %s", format_hex(seed, seed_len, 0, &gc));
-
-    int chunk = md_kt_size(md_kt);
-    unsigned int A1_len = md_kt_size(md_kt);
-
-    hmac_ctx_init(ctx, sec, sec_len, md_kt);
-    hmac_ctx_init(ctx_tmp, sec, sec_len, md_kt);
-
-    hmac_ctx_update(ctx,seed,seed_len);
-    hmac_ctx_final(ctx, A1);
-
-    for (;; )
-    {
-        hmac_ctx_reset(ctx);
-        hmac_ctx_reset(ctx_tmp);
-        hmac_ctx_update(ctx,A1,A1_len);
-        hmac_ctx_update(ctx_tmp,A1,A1_len);
-        hmac_ctx_update(ctx,seed,seed_len);
-
-        if (olen > chunk)
-        {
-            hmac_ctx_final(ctx, out);
-            out += chunk;
-            olen -= chunk;
-            hmac_ctx_final(ctx_tmp, A1); /* calc the next A1 value */
-        }
-        else    /* last one */
-        {
-            hmac_ctx_final(ctx, A1);
-            memcpy(out,A1,olen);
-            break;
-        }
-    }
-    hmac_ctx_cleanup(ctx);
-    hmac_ctx_free(ctx);
-    hmac_ctx_cleanup(ctx_tmp);
-    hmac_ctx_free(ctx_tmp);
-    secure_memzero(A1, sizeof(A1));
-
-    dmsg(D_SHOW_KEY_SOURCE, "tls1_P_hash out: %s", format_hex(out_orig, olen_orig, 0, &gc));
-    gc_free(&gc);
-}
-
-/*
- * Use the TLS PRF function for generating data channel keys.
- * This code is based on the OpenSSL library.
- *
- * TLS generates keys as such:
- *
- * master_secret[48] = PRF(pre_master_secret[48], "master secret",
- *                         ClientHello.random[32] + ServerHello.random[32])
- *
- * key_block[] = PRF(SecurityParameters.master_secret[48],
- *                 "key expansion",
- *                 SecurityParameters.server_random[32] +
- *                 SecurityParameters.client_random[32]);
- *
- * Notes:
- *
- * (1) key_block contains a full set of 4 keys.
- * (2) The pre-master secret is generated by the client.
- */
-static void
-tls1_PRF(const uint8_t *label,
-         int label_len,
-         const uint8_t *sec,
-         int slen,
-         uint8_t *out1,
-         int olen)
-{
-    struct gc_arena gc = gc_new();
-    const md_kt_t *md5 = md_kt_get("MD5");
-    const md_kt_t *sha1 = md_kt_get("SHA1");
-
-    uint8_t *out2 = (uint8_t *) gc_malloc(olen, false, &gc);
-
-    int len = slen/2;
-    const uint8_t *S1 = sec;
-    const uint8_t *S2 = &(sec[len]);
-    len += (slen&1); /* add for odd, make longer */
-
-    tls1_P_hash(md5,S1,len,label,label_len,out1,olen);
-    tls1_P_hash(sha1,S2,len,label,label_len,out2,olen);
-
-    for (int i = 0; i<olen; i++)
-    {
-        out1[i] ^= out2[i];
-    }
-
-    secure_memzero(out2, olen);
-
-    dmsg(D_SHOW_KEY_SOURCE, "tls1_PRF out[%d]: %s", olen, format_hex(out1, olen, 0, &gc));
-
-    gc_free(&gc);
-}
-
 static void
 openvpn_PRF(const uint8_t *secret,
             int secret_len,
@@ -1757,7 +1629,7 @@  openvpn_PRF(const uint8_t *secret,
     }
 
     /* compute PRF */
-    tls1_PRF(BPTR(&seed), BLEN(&seed), secret, secret_len, output, output_len);
+    ssl_tls1_PRF(BPTR(&seed), BLEN(&seed), secret, secret_len, output, output_len);
 
     buf_clear(&seed);
     free_buf(&seed);
diff --git a/tests/unit_tests/openvpn/test_crypto.c b/tests/unit_tests/openvpn/test_crypto.c
index ea9b99b2..6c68099e 100644
--- a/tests/unit_tests/openvpn/test_crypto.c
+++ b/tests/unit_tests/openvpn/test_crypto.c
@@ -38,6 +38,7 @@ 
 #include <cmocka.h>
 
 #include "crypto.h"
+#include "ssl_backend.h"
 
 #include "mock_msg.h"
 
@@ -136,12 +137,43 @@  crypto_translate_cipher_names(void **state)
     test_cipher_names("id-aes256-GCM", "AES-256-GCM");
 }
 
+
+static uint8_t good_prf[32] = {0xd9, 0x8c, 0x85, 0x18, 0xc8, 0x5e, 0x94, 0x69,
+                               0x27, 0x91, 0x6a, 0xcf, 0xc2, 0xd5, 0x92, 0xfb,
+                               0xb1, 0x56, 0x7e, 0x4b, 0x4b, 0x14, 0x59, 0xe6,
+                               0xa9, 0x04, 0xac, 0x2d, 0xda, 0xb7, 0x2d, 0x67};
+static void
+crypto_test_tls_prf(void **state)
+{
+    const char *seedstr = "Quis aute iure reprehenderit in voluptate "
+                          "velit esse cillum dolore";
+    const unsigned char *seed = (const unsigned char *) seedstr;
+    const size_t seed_len = strlen(seedstr);
+
+
+
+
+    const char* ipsumlorem = "Lorem ipsum dolor sit amet, consectetur "
+                             "adipisici elit, sed eiusmod tempor incidunt ut "
+                             "labore et dolore magna aliqua.";
+
+    const unsigned char *secret = (const unsigned char *) ipsumlorem;
+    size_t secret_len = strlen((const char *)secret);
+
+
+    uint8_t out[32];
+    ssl_tls1_PRF(seed, seed_len, secret, secret_len, out, sizeof(out));
+
+    assert_memory_equal(good_prf, out, sizeof(out));
+}
+
 int
 main(void)
 {
     const struct CMUnitTest tests[] = {
         cmocka_unit_test(crypto_pem_encode_decode_loopback),
         cmocka_unit_test(crypto_translate_cipher_names),
+        cmocka_unit_test(crypto_test_tls_prf)
     };
 
 #if defined(ENABLE_CRYPTO_OPENSSL)