Bugfix: Fix panic when passing an out parameter to seal() that is lon…

…ger than the minimum required length. Fixing this required to explicitly defining the length when copying the slice to append to authentication tag to the ciphertext

src/hazardous/aead/chacha20poly1305.rs

@@ -195,7 +195,7 @@ pub fn seal(
 	let mut poly1305_state = poly1305::init(&poly1305_key);
 
 	process_authentication(&mut poly1305_state, &optional_ad, &dst_out, plaintext.len())?;
-	dst_out[plaintext.len()..].copy_from_slice(&poly1305_state.finalize()?.unprotected_as_bytes());
+	dst_out[plaintext.len()..(plaintext.len() + POLY1305_BLOCKSIZE)].copy_from_slice(&poly1305_state.finalize()?.unprotected_as_bytes());
 
 	Ok(())
 }
@@ -456,3 +456,33 @@ fn rfc_8439_test_poly1305_key_gen_3() {
 		expected.as_ref()
 	);
 }
+
+#[test]
+fn regression_detect_bigger_than_slice_bug() {
+
+    let pt = [0x5B; 79];
+
+    let mut dst_out_ct = vec![0u8; pt.len() + (POLY1305_BLOCKSIZE * 2)];
+
+	seal(
+		&SecretKey::from_slice(&[0u8; 32]).unwrap(),
+		&Nonce::from_slice(&[0u8; 12]).unwrap(),
+		&pt[..],
+		None,
+		&mut dst_out_ct,
+	).unwrap();
+
+	// Verify that using a slice that is bigger than produces the exact same
+	// output as using a slice that is the exact required length
+    let mut dst_out_ct_2 = vec![0u8; pt.len() + POLY1305_BLOCKSIZE];
+
+    seal(
+		&SecretKey::from_slice(&[0u8; 32]).unwrap(),
+		&Nonce::from_slice(&[0u8; 12]).unwrap(),
+		&pt[..],
+		None,
+		&mut dst_out_ct_2,
+	).unwrap();
+
+    assert!(dst_out_ct[..dst_out_ct_2.len()] == dst_out_ct_2[..]);
+}

src/hazardous/aead/xchacha20poly1305.rs

@@ -171,3 +171,33 @@ fn test_modified_tag_error() {
 	)
 	.is_err());
 }
+
+#[test]
+fn regression_detect_bigger_than_slice_bug() {
+
+    let pt = [0x5B; 79];
+
+    let mut dst_out_ct = vec![0u8; pt.len() + (16 * 2)];
+
+	seal(
+		&SecretKey::from_slice(&[0u8; 32]).unwrap(),
+		&Nonce::from_slice(&[0u8; 24]).unwrap(),
+		&pt[..],
+		None,
+		&mut dst_out_ct,
+	).unwrap();
+
+	// Verify that using a slice that is bigger than produces the exact same
+	// output as using a slice that is the exact required length
+    let mut dst_out_ct_2 = vec![0u8; pt.len() + 16];
+
+    seal(
+		&SecretKey::from_slice(&[0u8; 32]).unwrap(),
+		&Nonce::from_slice(&[0u8; 24]).unwrap(),
+		&pt[..],
+		None,
+		&mut dst_out_ct_2,
+	).unwrap();
+
+    assert!(dst_out_ct[..dst_out_ct_2.len()] == dst_out_ct_2[..]);
+}