1 files changed, 58 insertions, 0 deletions
diff --git a/src/passwordmaker/hmac.rs b/src/passwordmaker/hmac.rs
new file mode 100644
index 0000000..4c9d6aa
--- /dev/null
+++ b/src/passwordmaker/hmac.rs
@@ -0,0 +1,58 @@
+use crate::Hasher;
+
+pub(super) fn hmac<T, K, M>(key : K, data : M) -> T::Output
+    where T : Hasher,
+    T::Output : AsRef<[u8]>,
+    K : Iterator<Item=u8> + Clone,
+    M : Iterator<Item=u8>,
+{
+    let key_len = key.clone().count();
+    let key =  if key_len > 64 {
+        KeyOrHash::from_hash(T::hash(&key.collect::<Vec<_>>()))
+    } else {
+        KeyOrHash::from_key(key)
+    };
+    let key = key.chain(std::iter::repeat(0)); //if key[i] does not exist, use 0 instead.
+
+    let mut inner_pad = [0u8;64];
+    let mut outer_pad = [0u8;64];
+
+    let pads = inner_pad.iter_mut().zip(outer_pad.iter_mut());
+    for ((i,o),k) in pads.zip(key) {
+        *i = k ^ 0x36;
+        *o = k ^ 0x5C;
+    }
+
+    let hash = T::hash(&inner_pad.iter().copied().chain(data).collect::<Vec<_>>());
+    T::hash(&outer_pad.iter().chain(hash.as_ref().iter()).copied().collect::<Vec<_>>())
+}
+
+enum KeyOrHash<K: Iterator<Item=u8>, H: AsRef<[u8]>> {
+    Key(K),
+    Hash{
+        hash : H,
+        idx : usize
+    }
+}
+
+impl<K: Iterator<Item=u8>, H: AsRef<[u8]>> KeyOrHash<K, H>{
+    fn from_key(key : K) -> Self {
+        Self::Key(key)
+    }
+    fn from_hash(hash : H) -> Self {
+        Self::Hash { hash, idx: 0 }
+    }
+}
+
+impl<K: Iterator<Item=u8>, H: AsRef<[u8]>> Iterator for KeyOrHash<K, H>{
+    type Item = u8;
+    fn next(&mut self) -> Option<Self::Item> {
+        match self {
+            KeyOrHash::Key(k) => k.next(),
+            KeyOrHash::Hash { hash: owned, idx } => {
+                *idx += 1;
+                owned.as_ref().get(*idx-1).copied()
+            },
+        }
+    }
+}
+\ No newline at end of file