Implement HKDF from RFC5869

This is a customizable extract-and-expand HMAC-KDF for deriving keys.
It derives from RFC5869, which derives its rationale from Krawczyk,
H., "Cryptographic Extraction and Key Derivation: The HKDF Scheme",
Proceedings of CRYPTO 2010, 2010, <http://eprint.iacr.org/2010/264>.

I'm also renaming the existing KDF, now that Tor has two of them.

This is the key derivation scheme specified in ntor.

There are also unit tests.

1 files changed, 51 insertions, 0 deletions

diff --git a/src/test/test_crypto.c b/src/test/test_crypto.c
index fd983de00..6c731386d 100644
--- a/src/test/test_crypto.c
+++ b/src/test/test_crypto.c
@@ -832,6 +832,56 @@ test_crypto_base32_decode(void)
   ;
 }
 
+static void
+test_crypto_hkdf_sha256(void *arg)
+{
+  uint8_t key_material[100];
+  const uint8_t salt[] = "ntor-curve25519-sha256-1:key_extract";
+  const size_t salt_len = strlen((char*)salt);
+  const uint8_t m_expand[] = "ntor-curve25519-sha256-1:key_expand";
+  const size_t m_expand_len = strlen((char*)m_expand);
+  int r;
+  char *mem_op_hex_tmp = NULL;
+
+  (void)arg;
+
+#define EXPAND(s) \
+  r = crypto_expand_key_material_rfc5869_sha256( \
+    (const uint8_t*)(s), strlen(s),              \
+    salt, salt_len,                              \
+    m_expand, m_expand_len,                      \
+    key_material, 100)
+
+  /* Test vectors generated with ntor_ref.py */
+  memset(key_material, 0, sizeof(key_material));
+  EXPAND("");
+  tt_int_op(r, ==, 0);
+  test_memeq_hex(key_material,
+                 "d3490ed48b12a48f9547861583573fe3f19aafe3f81dc7fc75"
+                 "eeed96d741b3290f941576c1f9f0b2d463d1ec7ab2c6bf71cd"
+                 "d7f826c6298c00dbfe6711635d7005f0269493edf6046cc7e7"
+                 "dcf6abe0d20c77cf363e8ffe358927817a3d3e73712cee28d8");
+
+  EXPAND("Tor");
+  tt_int_op(r, ==, 0);
+  test_memeq_hex(key_material,
+                 "5521492a85139a8d9107a2d5c0d9c91610d0f95989975ebee6"
+                 "c02a4f8d622a6cfdf9b7c7edd3832e2760ded1eac309b76f8d"
+                 "66c4a3c4d6225429b3a016e3c3d45911152fc87bc2de9630c3"
+                 "961be9fdb9f93197ea8e5977180801926d3321fa21513e59ac");
+
+  EXPAND("AN ALARMING ITEM TO FIND ON YOUR CREDIT-RATING STATEMENT");
+  tt_int_op(r, ==, 0);
+  test_memeq_hex(key_material,
+                 "a2aa9b50da7e481d30463adb8f233ff06e9571a0ca6ab6df0f"
+                 "b206fa34e5bc78d063fc291501beec53b36e5a0e434561200c"
+                 "5f8bd13e0f88b3459600b4dc21d69363e2895321c06184879d"
+                 "94b18f078411be70b767c7fc40679a9440a0c95ea83a23efbf");
+
+ done:
+  tor_free(mem_op_hex_tmp);
+}
+
 static void *
 pass_data_setup_fn(const struct testcase_t *testcase)
 {
@@ -863,6 +913,7 @@ struct testcase_t crypto_tests[] = {
   { "aes_iv_AES", test_crypto_aes_iv, TT_FORK, &pass_data, (void*)"aes" },
   { "aes_iv_EVP", test_crypto_aes_iv, TT_FORK, &pass_data, (void*)"evp" },
   CRYPTO_LEGACY(base32_decode),
+  { "hkdf_sha256", test_crypto_hkdf_sha256, 0, NULL, NULL },
   END_OF_TESTCASES
 };