poly1305: Use MacResult for representing tags

This outsources constant time comparisons to `MacResult`, so downstream
crates don't need to rely on additional crates to perform them beyond
what `MacResult` is already using.

poly1305/Cargo.toml

@@ -12,6 +12,7 @@ readme = "README.md"
 
 [dependencies]
 byteorder = { version = "1", default-features = false }
+crypto-mac = "0.7"
 zeroize = { version = "0.9", optional = true, default-features = false }
 
 [dev-dependencies]

poly1305/src/lib.rs

@@ -18,12 +18,15 @@
 
 // TODO: replace with `u32::{from_le_bytes, to_le_bytes}` in libcore (1.32+)
 extern crate byteorder;
+extern crate crypto_mac;
 
 #[cfg(feature = "zeroize")]
 extern crate zeroize;
 
 use byteorder::{ByteOrder, LE};
 use core::cmp::min;
+use crypto_mac::generic_array::{typenum::U16, GenericArray};
+use crypto_mac::MacResult;
 #[cfg(feature = "zeroize")]
 use zeroize::Zeroize;
 
@@ -33,6 +36,9 @@ pub const KEY_SIZE: usize = 32;
 /// Size of the blocks Poly1305 acts upon
 pub const BLOCK_SIZE: usize = 16;
 
+/// Poly1305 authentication tags
+pub type Tag = MacResult<U16>;
+
 /// The Poly1305 universal hash function.
 ///
 /// Note that Poly1305 is not a traditional MAC and is single-use only
@@ -135,7 +141,7 @@ impl Poly1305 {
     }
 
     /// Get the hashed output
-    pub fn result(mut self) -> [u8; BLOCK_SIZE] {
+    pub fn result(mut self) -> Tag {
         if self.leftover > 0 {
             self.buffer[self.leftover] = 1;
 
@@ -227,13 +233,13 @@ impl Poly1305 {
         f = u64::from(h3) + u64::from(self.pad[3]) + (f >> 32);
         h3 = f as u32;
 
-        let mut output = [0u8; BLOCK_SIZE];
-        LE::write_u32(&mut output[0..4], h0);
-        LE::write_u32(&mut output[4..8], h1);
-        LE::write_u32(&mut output[8..12], h2);
-        LE::write_u32(&mut output[12..16], h3);
+        let mut tag = GenericArray::default();
+        LE::write_u32(&mut tag[0..4], h0);
+        LE::write_u32(&mut tag[4..8], h1);
+        LE::write_u32(&mut tag[8..12], h2);
+        LE::write_u32(&mut tag[12..16], h3);
 
-        output
+        MacResult::new(tag)
     }
 
     /// Compute a single block of Poly1305 using the internal buffer

poly1305/tests/lib.rs

@@ -28,9 +28,10 @@ fn test_nacl_vector() {
         0xd9,
     ];
 
-    assert_eq!(&Poly1305::new(&key).chain(&msg).result(), &expected[..]);
+    let result1 = Poly1305::new(&key).chain(&msg).result();
+    assert_eq!(&expected[..], result1.code().as_slice());
 
-    let result = Poly1305::new(&key)
+    let result2 = Poly1305::new(&key)
         .chain(&msg[0..32])
         .chain(&msg[32..96])
         .chain(&msg[96..112])
@@ -44,7 +45,7 @@ fn test_nacl_vector() {
         .chain(&msg[130..131])
         .result();
 
-    assert_eq!(&result, &expected[..]);
+    assert_eq!(&expected[..], result2.code().as_slice());
 }
 
 #[test]
@@ -65,10 +66,9 @@ fn donna_self_test() {
         0x00,
     ];
 
-    assert_eq!(
-        &Poly1305::new(&wrap_key).chain(&wrap_msg).result(),
-        &wrap_mac[..]
-    );
+    let result = Poly1305::new(&wrap_key).chain(&wrap_msg).result();
+
+    assert_eq!(&wrap_mac[..], result.code().as_slice());
 
     let total_key = [
         0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0xff, 0xfe, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xff,
@@ -88,31 +88,35 @@ fn donna_self_test() {
         key.copy_from_slice(&repeat(i as u8).take(KEY_SIZE).collect::<Vec<_>>());
 
         let msg: Vec<u8> = repeat(i as u8).take(256).collect();
-        tpoly.input(&Poly1305::new(&key).chain(&msg[..i]).result());
+        let tag = Poly1305::new(&key).chain(&msg[..i]).result();
+        tpoly.input(tag.code().as_slice());
     }
 
-    assert_eq!(&tpoly.result(), &total_mac[..]);
+    assert_eq!(&total_mac[..], tpoly.result().code().as_slice());
 }
 
 #[test]
 fn test_tls_vectors() {
     // from http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-04
     let key = b"this is 32-byte key for Poly1305";
-    let msg = [0u8; 32];
-    let expected = [
+
+    let msg1 = [0u8; 32];
+    let expected1 = [
         0x49, 0xec, 0x78, 0x09, 0x0e, 0x48, 0x1e, 0xc6, 0xc2, 0x6b, 0x33, 0xb9, 0x1c, 0xcc, 0x03,
         0x07,
     ];
 
-    assert_eq!(&Poly1305::new(&key).chain(&msg).result(), &expected[..]);
+    let result1 = Poly1305::new(&key).chain(&msg1).result();
+    assert_eq!(&expected1[..], result1.code().as_slice());
 
-    let msg = b"Hello world!";
-    let expected = [
+    let msg2 = b"Hello world!";
+    let expected2 = [
         0xa6, 0xf7, 0x45, 0x00, 0x8f, 0x81, 0xc9, 0x16, 0xa2, 0x0d, 0xcc, 0x74, 0xee, 0xf2, 0xb2,
         0xf0,
     ];
 
-    assert_eq!(&Poly1305::new(&key).chain(&msg[..]).result(), &expected[..]);
+    let result2 = Poly1305::new(&key).chain(&msg2[..]).result();
+    assert_eq!(&expected2[..], result2.code().as_slice());
 }
 
 #[test]
@@ -135,5 +139,5 @@ fn padded_input() {
 
     let mut poly = Poly1305::new(&key);
     poly.input_padded(&msg);
-    assert_eq!(&expected[..], poly.result());
+    assert_eq!(&expected[..], poly.result().code().as_slice());
 }