working aes implementation

This patch adds a working AES256-GCM-SIV implementation, complete with one unit test. That test should be sufficient coverage, but in case it isn't, more tests can be added in the future.

Signed-off-by: Amy Parker <amy@amyip.net>

Cargo.toml

@@ -3,6 +3,8 @@ name = "libacc"
 version = "0.1.0"
 edition = "2021"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
-
 [dependencies]
+aes-gcm-siv = "0.11.1"
+rand = "0.8.5"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

src/aes.rs

@@ -1,13 +1,57 @@
+use std::io::{Error, ErrorKind};
+
+use aes_gcm_siv::{
+    aead::{Aead, OsRng},
+    Aes256GcmSiv, KeyInit, Nonce,
+};
+use rand::RngCore;
+
 /// Generates AES-encrypted packet from key.
 /// Returns the encrypted packet with appended nonce,
 /// which is really only the first 96 bits of the last 16 bytes.
-fn encapsulate(pkt: &[u8], key: &[u8]) -> Vec<u8> {
-    unimplemented!()
+fn encapsulate(pkt: &[u8], key: &[u8]) -> Result<Vec<u8>, std::io::Error> {
+    if key.len() != 32 {
+        return Err(Error::from(ErrorKind::InvalidInput));
+    }
+    let mut rng: rand::rngs::ThreadRng = rand::thread_rng();
+    let mut nonce_raw: [u8; 12] = [0u8; 12];
+    rng.fill_bytes(&mut nonce_raw);
+    let cipher = Aes256GcmSiv::new(key.into());
+    let nonce = Nonce::from_slice(&nonce_raw);
+    let mut cpt: Vec<u8> = match cipher.encrypt(nonce, pkt) {
+        Ok(v) => v,
+        Err(_) => return Err(Error::from(ErrorKind::InvalidData)),
+    };
+    cpt.extend(&nonce_raw);
+    Ok(cpt)
 }
 
 /// Attempts to decrypt AES with a given key.
 /// If this fails, returns Err.
 /// On success, returns Ok(Vec<u8>) containing the packet.
-fn reveal(pkt: &[u8]) -> Result<Vec<u8>, std::io::Error> {
-    unimplemented!()
+fn reveal(pkt: &[u8], key: &[u8]) -> Result<Vec<u8>, std::io::Error> {
+    if key.len() != 32 {
+        return Err(Error::from(ErrorKind::InvalidInput));
+    }
+    let l0: usize = pkt.len();
+    let nonce = Nonce::from_slice(&pkt[l0 - 12..]);
+    let pkt = &pkt[..l0 - 12];
+    let cipher = Aes256GcmSiv::new(key.into());
+    match cipher.decrypt(nonce, pkt) {
+        Ok(v) => Ok(v),
+        Err(_) => Err(Error::from(ErrorKind::InvalidData)),
+    }
+    //unimplemented!()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn enc_rev_pkts_aes256_single_rand() {
+        let key = Aes256GcmSiv::generate_key(OsRng);
+        let pkt = b"This is a sample packet for encryption with AES256-GCM-SIV!";
+        assert_eq!(reveal(&encapsulate(pkt, &key).unwrap(), &key).unwrap(), pkt);
+    }
 }