utils: add general fixed-key AES implementation

utils/Cargo.toml

@@ -6,3 +6,5 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+aes = "0.8.1"
+rand = "0.8.5"

utils/src/fixed_key_aes.rs

@@ -0,0 +1,61 @@
+use aes::cipher::crypto_common::Block;
+use aes::cipher::{BlockEncrypt, KeyInit};
+use aes::Aes128;
+use rand::{thread_rng, Rng};
+
+/// Fixed-key AES implementation.  Implements the ((tweakable) circular) correlation robust hash
+/// functions from Guo et al. eprint 2019/074
+#[derive(Clone, Debug)]
+pub struct FixedKeyAes {
+    /// AES object including expanded key.
+    aes: Aes128,
+}
+
+impl FixedKeyAes {
+    pub fn new(key: [u8; 16]) -> Self {
+        Self {
+            aes: Aes128::new_from_slice(&key).expect("does not fail since key has the right size"),
+        }
+    }
+
+    pub fn sample() -> Self {
+        let key: [u8; 16] = thread_rng().gen();
+        Self::new(key)
+    }
+
+    /// Permutation sigma(x) = (x.high64 ^ x.low64, x.high64).
+    fn sigma(x: u128) -> u128 {
+        let low = x & 0xffffffffffffffff;
+        let high = x >> 64;
+        ((high ^ low) << 64) | high
+    }
+
+    /// Random permutation pi(x) = AES(k, x)
+    fn pi(&self, x: u128) -> u128 {
+        let mut block = Block::<Aes128>::clone_from_slice(&x.to_le_bytes());
+        self.aes.encrypt_block(&mut block);
+        u128::from_le_bytes(
+            block
+                .as_slice()
+                .try_into()
+                .expect("does not fail since block is 16 bytes long"),
+        )
+    }
+
+    /// MMO function pi(x) ^ x
+    pub fn hash_cr(&self, x: u128) -> u128 {
+        self.pi(x) ^ x
+    }
+
+    /// MMO-hat function pi(sigma(x)) ^ sigma(x)
+    pub fn hash_ccr(&self, x: u128) -> u128 {
+        let sigma_x = Self::sigma(x);
+        self.pi(sigma_x) ^ sigma_x
+    }
+
+    /// TMMO function pi(pi(x) ^ i) ^ pi(x)
+    pub fn hash_tccr(&self, x: u128, tweak: u128) -> u128 {
+        let pi_x = self.pi(x);
+        self.pi(pi_x ^ tweak) ^ pi_x
+    }
+}

utils/src/lib.rs

@@ -0,0 +1 @@
+pub mod fixed_key_aes;