diff --git a/rust/radix204/src/base16.rs b/rust/radix204/src/base16.rs
new file mode 100644
--- /dev/null
+++ b/rust/radix204/src/base16.rs
@@ -0,0 +1,73 @@
+// Copyright 2017 Facebook, Inc.
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+
+//! Base16 iterators
+
+pub trait ToBase16Iter<'a, T> {
+    fn to_base16iter(&'a self) -> T;
+}
+
+impl<'a, T: AsRef<[u8]>> ToBase16Iter<'a, SliceBase16Iter<'a, T>> for T {
+    #[inline]
+    fn to_base16iter(&'a self) -> SliceBase16Iter<'a, T> { SliceBase16Iter(self, 0) }
+}
+
+/// Base16 iterator for [u8]
+pub struct SliceBase16Iter<'a, T: 'a>(&'a T, usize);
+
+impl<'a, T: AsRef<[u8]>> Iterator for SliceBase16Iter<'a, T> {
+    type Item = u8;
+
+    #[inline]
+    fn next(&mut self) -> Option<u8> {
+        let i = self.1;
+        match self.0.as_ref().get(i / 2) {
+            Some(v) => {
+                self.1 += 1;
+                if i & 1 == 0 { v >> 4 } else { v & 0xf }.into()
+            }
+            None => None,
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.0.as_ref().len() * 2 - self.1;
+        (len, Some(len))
+    }
+
+    #[inline]
+    fn count(self) -> usize { self.0.as_ref().len() * 2 }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use types::Key;
+    use test::Bencher;
+
+    // rustfmt makes code much longer
+    #[test]
+    #[cfg_attr(rustfmt, rustfmt_skip)]
+    fn test_key() {
+        let x: Key = [
+            0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xde, 0xef, 0xfa, 0xa1, 0xa2, 0xa3, 0xa4,
+            0xa5, 0x00, 0x91, 0x92, 0x93, 0x56].into();
+        assert_eq!(x.to_base16iter().count(), 40);
+        let y: Vec<u8> = x.to_base16iter().collect();
+        assert_eq!(y, vec![
+            1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 10, 11, 12, 13, 13, 14, 14, 15, 15, 10, 10, 1, 10, 2, 10,
+            3, 10, 4, 10, 5, 0, 0, 9, 1, 9, 2, 9, 3, 5, 6]);
+    }
+
+    #[bench]
+    fn bench_key_base64(b: &mut Bencher) {
+        let x: Key = [4u8; 20].into(); // change 20 to Key::len() when const fn is stable
+        b.iter(|| {
+            let y: u8 = x.to_base16iter().sum();
+            assert_eq!(y, 4 * Key::fixed_len() as u8);
+        })
+    }
+}
diff --git a/rust/radix204/src/lib.rs b/rust/radix204/src/lib.rs
--- a/rust/radix204/src/lib.rs
+++ b/rust/radix204/src/lib.rs
@@ -22,3 +22,4 @@
 
 pub mod types;
 pub mod errors;
+pub mod base16;