change key length

Cargo.toml

@@ -10,3 +10,8 @@ subtle = "2.6.1"
 
 [dev-dependencies]
 tempfile = "3.27.0"
+
+[profile.release]
+strip = true
+lto = true
+panic = "abort"

src/kdf/kdf.rs

@@ -1,23 +1,21 @@
 //! Password-to-key derivation.
 //!
-//! This currently uses SHA3-256 directly and truncates the result to 24 bytes
-//! because `KeccakAead` accepts keys up to 24 bytes.
+//! This currently uses SHA3-512 directly
 //!
 //! This is not a proper password-based KDF. There is currently no salt,
 //! work factor, memory hardness, or iteration count.
 
-use crate::keccak::sha3_256;
+use crate::keccak::sha3_512;
 
 /// Length of the key produced for `KeccakAead`.
-pub const DERIVED_KEY_LEN: usize = 24;
+pub const DERIVED_KEY_LEN: usize = 64;
 
-/// Derive a 24-byte encryption key from a password.
+/// Derive a 64-byte encryption key from a password.
 ///
 /// The password is encoded as UTF-8 and hashed using the project's
-/// SHA3-256 implementation. The first 24 bytes of the digest are used
-/// as the AEAD key.
+/// SHA3-512 implementation.
 pub fn derive_file_key(password: &str) -> [u8; DERIVED_KEY_LEN] {
-    let digest = sha3_256(password.as_bytes());
+    let digest = sha3_512(password.as_bytes());
 
     let mut key = [0u8; DERIVED_KEY_LEN];
     key.copy_from_slice(&digest[..DERIVED_KEY_LEN]);

src/kdf/test.rs

@@ -3,7 +3,7 @@ use crate::kdf::kdf::DERIVED_KEY_LEN;
 
 #[test]
 fn key_has_expected_length() {
-    assert_eq!(DERIVED_KEY_LEN, 24);
+    assert_eq!(DERIVED_KEY_LEN, 64);
 
     let key = derive_file_key("test password");
     assert_eq!(key.len(), DERIVED_KEY_LEN);

src/keccak_aead.rs

@@ -1,9 +1,11 @@
 use crate::keccak::shake256;
 
 const RATE_SIZE: usize = 16;
-const CAPACITY_SIZE: usize = 24;
+const CAPACITY_SIZE: usize = 64;
 const STATE_SIZE: usize = RATE_SIZE + CAPACITY_SIZE;
 const CHUNK_SIZE: usize = 16;
+const MIN_KEY_SIZE: usize = 16;
+const MAX_KEY_SIZE: usize = 64;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct EncryptionResult {
@@ -23,13 +25,19 @@ pub struct KeccakAead {
 }
 
 impl KeccakAead {
+    #[inline]
+    fn assert_valid_key_size(key: &[u8]) {
+        assert!(
+            (MIN_KEY_SIZE..=MAX_KEY_SIZE).contains(&key.len()),
+            "key must be between {} and {} bytes",
+            MIN_KEY_SIZE,
+            MAX_KEY_SIZE
+        );
+    }
+
     /// Initialize the AEAD state.
     pub fn new(iv: &[u8], key: &[u8], nonce: &[u8]) -> Self {
-        assert!(
-            key.len() <= CAPACITY_SIZE,
-            "key must be at most {} bytes",
-            CAPACITY_SIZE
-        );
+        Self::assert_valid_key_size(key);
 
         let mut input = Vec::with_capacity(iv.len() + key.len() + nonce.len());
 
@@ -42,8 +50,8 @@ impl KeccakAead {
         let mut state = [0u8; STATE_SIZE];
         state.copy_from_slice(&squeezed);
 
-        for i in 0..key.len() {
-            state[RATE_SIZE + i] ^= key[i];
+        for (i, &byte) in key.iter().enumerate() {
+            state[RATE_SIZE + i] ^= byte;
         }
 
         Self { state }
@@ -60,8 +68,9 @@ impl KeccakAead {
                 input[i] = byte ^ self.state[i];
             }
 
-            // c = state[16..40]
-            input[RATE_SIZE..STATE_SIZE].copy_from_slice(&self.state[RATE_SIZE..STATE_SIZE]);
+            // c = state[16..48]
+            input[RATE_SIZE..STATE_SIZE]
+                .copy_from_slice(&self.state[RATE_SIZE..STATE_SIZE]);
 
             self.state = shake256_state(&input);
         }
@@ -70,7 +79,7 @@ impl KeccakAead {
     }
 
     /// Encrypt plaintext.
-    /// Returns the ciphertext split logically into 16-byte chunks, then concatenated
+    /// Returns the ciphertext split logically into 16-byte chunks, then concatenated.
     pub fn plaintext_processing(&mut self, plaintext: &[u8]) -> Vec<u8> {
         let mut ciphertext = Vec::with_capacity(plaintext.len());
 
@@ -89,7 +98,8 @@ impl KeccakAead {
 
             input[..chunk.len()].copy_from_slice(&ciphertext[start..]);
 
-            input[RATE_SIZE..STATE_SIZE].copy_from_slice(&self.state[RATE_SIZE..STATE_SIZE]);
+            input[RATE_SIZE..STATE_SIZE]
+                .copy_from_slice(&self.state[RATE_SIZE..STATE_SIZE]);
 
             self.state = shake256_state(&input);
         }
@@ -112,7 +122,8 @@ impl KeccakAead {
             // input = ciphertext || c
             input[..chunk.len()].copy_from_slice(chunk);
 
-            input[RATE_SIZE..STATE_SIZE].copy_from_slice(&self.state[RATE_SIZE..STATE_SIZE]);
+            input[RATE_SIZE..STATE_SIZE]
+                .copy_from_slice(&self.state[RATE_SIZE..STATE_SIZE]);
 
             self.state = shake256_state(&input);
         }
@@ -123,11 +134,7 @@ impl KeccakAead {
     /// Finalize and generate the authentication tag.
     /// The tag has the same length as the key.
     pub fn finalize(&mut self, key: &[u8]) -> Vec<u8> {
-        assert!(
-            key.len() <= CAPACITY_SIZE,
-            "key must be at most {} bytes",
-            CAPACITY_SIZE
-        );
+        Self::assert_valid_key_size(key);
 
         // Construct padded key:
         let mut padded_key = [0u8; CAPACITY_SIZE];
@@ -137,22 +144,23 @@ impl KeccakAead {
         padded_key[padding_len..].copy_from_slice(key);
 
         // XOR padded key into c.
-        for (i, &byte) in padded_key.iter().enumerate().take(CAPACITY_SIZE) {
-            self.state[RATE_SIZE + i] ^= byte;
+        for (state_byte, &key_byte) in self.state[RATE_SIZE..STATE_SIZE]
+            .iter_mut()
+            .zip(padded_key.iter())
+        {
+            *state_byte ^= key_byte;
         }
 
-        // SHAKE256(state, 40)
+        // SHAKE256(state, 48)
         let output = shake256(&self.state, STATE_SIZE);
 
+        // Take the last `key.len()` bytes from the output.
         let tag_start = STATE_SIZE - key.len();
 
-        let mut tag = Vec::with_capacity(key.len());
-
-        for i in 0..key.len() {
-            tag.push(key[i] ^ output[tag_start + i]);
-        }
-
-        tag
+        key.iter()
+            .zip(&output[tag_start..])
+            .map(|(&key_byte, &output_byte)| key_byte ^ output_byte)
+            .collect()
     }
 
     /// Encrypt:
@@ -199,7 +207,7 @@ impl KeccakAead {
     }
 }
 
-/// SHAKE256 wrapper returning exactly a 40-byte AEAD state.
+/// SHAKE256 wrapper returning exactly a 48-byte AEAD state.
 #[inline]
 fn shake256_state(state: &[u8; STATE_SIZE]) -> [u8; STATE_SIZE] {
     let output = shake256(state, STATE_SIZE);
@@ -217,38 +225,44 @@ mod tests {
 
     #[test]
     fn encrypt_decrypt_roundtrip() {
-        let key = [0x00u8; 16];
+        for key_len in [16, 17, 24, 25, 31, 32] {
+            let key = vec![0x00u8; key_len];
             let iv = [0x11u8; 16];
             let nonce = [0x22u8; 16];
 
             let associated_data = b"associated data";
-
             let plaintext = b"Hello, Keccak AEAD!";
 
-        let encrypted = KeccakAead::encrypt(&key, plaintext, &iv, associated_data, &nonce);
+            let encrypted =
+                KeccakAead::encrypt(&key, plaintext, &iv, associated_data, &nonce);
 
-        let decrypted = KeccakAead::decrypt(&key, &encrypted.cipher, &iv, associated_data, &nonce);
+            let decrypted =
+                KeccakAead::decrypt(&key, &encrypted.cipher, &iv, associated_data, &nonce);
 
             assert_eq!(decrypted.plaintext, plaintext);
-
             assert_eq!(decrypted.tag, encrypted.tag);
+            assert_eq!(encrypted.tag.len(), key_len);
+        }
     }
 
     #[test]
     fn handles_empty_plaintext() {
-        let key = [0x42u8; 16];
+        for key_len in [16, 24, 32] {
+            let key = vec![0x42u8; key_len];
             let iv = [0x11u8; 16];
             let nonce = [0x22u8; 16];
 
             let result = KeccakAead::encrypt(&key, &[], &iv, b"test", &nonce);
 
             assert_eq!(result.cipher.len(), 0);
-        assert_eq!(result.tag.len(), key.len());
+            assert_eq!(result.tag.len(), key_len);
+        }
     }
 
     #[test]
     fn handles_empty_associated_data() {
-        let key = [0x42u8; 16];
+        for key_len in [16, 24, 32] {
+            let key = vec![0x42u8; key_len];
             let iv = [0x11u8; 16];
             let nonce = [0x22u8; 16];
 
@@ -256,16 +270,17 @@ mod tests {
 
             let result = KeccakAead::encrypt(&key, plaintext, &iv, &[], &nonce);
 
-        let decrypted = KeccakAead::decrypt(&key, &result.cipher, &iv, &[], &nonce);
+            let decrypted =
+                KeccakAead::decrypt(&key, &result.cipher, &iv, &[], &nonce);
 
             assert_eq!(decrypted.plaintext, plaintext);
-
             assert_eq!(decrypted.tag, result.tag);
         }
+    }
 
     #[test]
     fn handles_multiple_chunks() {
-        let key = [0x42u8; 16];
+        let key = [0x42u8; 32];
         let iv = [0x11u8; 16];
         let nonce = [0x22u8; 16];
 
@@ -274,39 +289,61 @@ mod tests {
 
         let associated_data = b"abcdefghijklmnopqrstuvwxyz";
 
-        let encrypted = KeccakAead::encrypt(&key, plaintext, &iv, associated_data, &nonce);
+        let encrypted =
+            KeccakAead::encrypt(&key, plaintext, &iv, associated_data, &nonce);
 
         assert_eq!(encrypted.cipher.len(), plaintext.len());
+        assert_eq!(encrypted.tag.len(), key.len());
 
         let decrypted = KeccakAead::decrypt(
             &key,
             &encrypted.cipher,
-            iv.as_slice(),
+            &iv,
             associated_data,
-            nonce.as_slice(),
+            &nonce,
         );
 
         assert_eq!(decrypted.plaintext, plaintext);
-
         assert_eq!(decrypted.tag, encrypted.tag);
     }
 
     #[test]
     fn tag_changes_when_ciphertext_changes() {
-        let key = [0x42u8; 16];
+        let key = [0x42u8; 32];
         let iv = [0x11u8; 16];
         let nonce = [0x22u8; 16];
 
         let plaintext = b"test plaintext";
 
-        let encrypted = KeccakAead::encrypt(&key, plaintext, &iv, b"ad", &nonce);
+        let encrypted =
+            KeccakAead::encrypt(&key, plaintext, &iv, b"ad", &nonce);
 
         let mut modified = encrypted.cipher.clone();
-
         modified[0] ^= 1;
 
-        let decrypted = KeccakAead::decrypt(&key, &modified, &iv, b"ad", &nonce);
+        let decrypted =
+            KeccakAead::decrypt(&key, &modified, &iv, b"ad", &nonce);
 
         assert_ne!(decrypted.tag, encrypted.tag);
     }
+
+    #[test]
+    #[should_panic(expected = "key must be between 16 and 64 bytes")]
+    fn rejects_short_key() {
+        let key = [0u8; 15];
+        let iv = [0u8; 16];
+        let nonce = [0u8; 16];
+
+        KeccakAead::encrypt(&key, b"test", &iv, b"", &nonce);
+    }
+
+    #[test]
+    #[should_panic(expected = "key must be between 16 and 64 bytes")]
+    fn rejects_long_key() {
+        let key = [0u8; 65];
+        let iv = [0u8; 16];
+        let nonce = [0u8; 16];
+
+        KeccakAead::encrypt(&key, b"test", &iv, b"", &nonce);
+    }
 }