Document aes related modules

src/aes.rs

@@ -1,3 +1,9 @@
+//! Implementation of the AES decryption for zip files.
+//!
+//! This was implemented according to the [WinZip specification](https://www.winzip.com/win/en/aes_info.html).
+//! Note that using CRC with AES depends on the specific encryption specification used, AE-1 or AE-2.
+//! AE-2 doesn't set the CRC field correctly, even though some zip files still have CRC set even with AE-2.
+
 use crate::aes_ctr;
 use constant_time_eq::constant_time_eq;
 use hmac::{Hmac, Mac, NewMac};

src/aes_ctr.rs

@@ -1,3 +1,9 @@
+//! A counter mode (CTR) for AES to work with the encryption used in zip files.
+//!
+//! This was implemented since the zip specification requires the mode to not use a nonce and uses a
+//! different byte order (little endian) than NIST (big endian).
+//! See [AesCtrZipKeyStream](./struct.AesCtrZipKeyStream.html) for more information.
+
 use aes::block_cipher::generic_array::GenericArray;
 use aes::{BlockCipher, NewBlockCipher};
 use byteorder::WriteBytesExt;