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, 9 insertions, 2 deletions

diff --git a/src/common/crypto.h b/src/common/crypto.h
index eb8b1de16..2d31e8d8b 100644
--- a/src/common/crypto.h
+++ b/src/common/crypto.h
@@ -239,8 +239,15 @@ ssize_t crypto_dh_compute_secret(int severity, crypto_dh_t *dh,
                              const char *pubkey, size_t pubkey_len,
                              char *secret_out, size_t secret_out_len);
 void crypto_dh_free(crypto_dh_t *dh);
-int crypto_expand_key_material(const char *key_in, size_t in_len,
-                               char *key_out, size_t key_out_len);
+
+int crypto_expand_key_material_TAP(const uint8_t *key_in,
+                                   size_t key_in_len,
+                                   uint8_t *key_out, size_t key_out_len);
+int crypto_expand_key_material_rfc5869_sha256(
+                                    const uint8_t *key_in, size_t key_in_len,
+                                    const uint8_t *salt_in, size_t salt_in_len,
+                                    const uint8_t *info_in, size_t info_in_len,
+                                    uint8_t *key_out, size_t key_out_len);
 
 /* random numbers */
 int crypto_seed_rng(int startup);