Symmetric state layer

src/enoise_crypto.erl

@@ -6,7 +6,7 @@
 
 -include("enoise.hrl").
 
--export([decrypt/5, encrypt/5, rekey/2, hash/2, pad/3, hashlen/1, dhlen/1, new_key_pair/1, hkdf/3, dh/3]).
+-export([decrypt/5, encrypt/5, rekey/2, hash/2, pad/3, hashlen/1, dhlen/1, new_key_pair/1, hmac/3, hkdf/3, dh/3]).
 
 new_key_pair(dh25519) ->
     KeyPair = enacl:crypto_sign_ed25519_keypair(),
@@ -16,7 +16,19 @@ new_key_pair(dh25519) ->
 dh(dh25519, KeyPair, PubKey) ->
     enacl:curve25519_scalarmult(KeyPair#key_pair.pik, PubKey).
 
-hkdf(_, _, _) -> [].
+hmac(Hash, Key, Data) ->
+    BLen = blocklen(blake2b),
+    Block1 = hmac_format_key(Hash, Key, 16#36, BLen),
+    Hash1 = hash(Hash, <<Block1/binary, Data/binary>>),
+    Block2 = hmac_format_key(Hash, Key, 16#5C, BLen),
+    hash(Hash, <<Block2/binary, Hash1/binary>>).
+
+hkdf(Hash, Key, Data) ->
+    TempKey = hmac(Hash, Key, Data),
+    Output1 = hmac(Hash, TempKey, <<1:8>>),
+    Output2 = hmac(Hash, TempKey, <<Output1/binary, 2:8>>),
+    Output3 = hmac(Hash, TempKey, <<Output2/binary, 3:8>>),
+    [Output1, Output2, Output3].
 
 rekey(Cipher, K) ->
     encrypt(Cipher, K, ?MAX_NONCE, <<>>, <<0:(32*8)>>).
@@ -32,9 +44,9 @@ decrypt('ChaChaPoly', K, N, Ad, CipherText) ->
     enacl:aead_chacha20poly1305_decrypt(K, N, Ad, CipherText).
 
 hash(blake2b, Data) ->
-    enacl:generichash(64, Data);
-hash(blake2s, Data) ->
-    enacl:generichash(32, Data).
+    {ok, Hash} = enacl:generichash(64, Data), Hash;
+hash(Hash, _Data) ->
+    error({hash_not_implemented_yet, Hash}).
 
 pad(Data, MinSize, PadByte) ->
     case byte_size(Data) of
@@ -50,5 +62,24 @@ hashlen(sha512)  -> 64;
 hashlen(blake2s) -> 32;
 hashlen(blake2b) -> 64.
 
+blocklen(sha256)  -> 64;
+blocklen(sha512)  -> 128;
+blocklen(blake2s) -> 64;
+blocklen(blake2b) -> 128.
+
 dhlen(dh25519) -> 32;
 dhlen(dh448)   -> 56.
+
+%%% Local implementations
+
+
+hmac_format_key(Hash, Key0, Pad, BLen) ->
+    Key1 =
+        case byte_size(Key0) =< BLen of
+            true  -> Key0;
+            false -> hash(Hash, Key0)
+        end,
+    Key2 = pad(Key1, BLen, 0),
+    <<PadWord:32>> = <<Pad:8, Pad:8, Pad:8, Pad:8>>,
+    << <<(Word bxor PadWord):32>> || <<Word:32>> <= Key2 >>.
+