reth_ecies/
mac.rs

1//! # Ethereum MAC Module
2//!
3//! This module provides the implementation of the Ethereum MAC (Message Authentication Code)
4//! construction, as specified in the Ethereum `RLPx` protocol.
5//!
6//! The Ethereum MAC is a nonstandard MAC construction that utilizes AES-256 (as a block cipher)
7//! and Keccak-256. It is specifically designed for messages of 128 bits in length and is not
8//! intended for general MAC use.
9//!
10//! For more information, refer to the [Ethereum MAC specification](https://github.com/ethereum/devp2p/blob/master/rlpx.md#mac).
11
12use aes::Aes256Enc;
13use alloy_primitives::{Keccak256, B128, B256};
14use block_padding::NoPadding;
15use cipher::BlockEncrypt;
16use digest::KeyInit;
17
18/// [`Ethereum MAC`](https://github.com/ethereum/devp2p/blob/master/rlpx.md#mac) state.
19///
20/// The ethereum MAC is a cursed MAC construction.
21///
22/// The ethereum MAC is a nonstandard MAC construction that uses AES-256 (without a mode, as a
23/// block cipher) and Keccak-256. However, it only ever encrypts messages that are 128 bits long,
24/// and is not defined as a general MAC.
25#[derive(Debug)]
26pub struct MAC {
27    secret: B256,
28    hasher: Keccak256,
29}
30
31impl MAC {
32    /// Initialize the MAC with the given secret
33    pub fn new(secret: B256) -> Self {
34        Self { secret, hasher: Keccak256::new() }
35    }
36
37    /// Update the internal keccak256 hasher with the given data
38    pub fn update(&mut self, data: &[u8]) {
39        self.hasher.update(data)
40    }
41
42    /// Accumulate the given header bytes into the MAC's internal state.
43    pub fn update_header(&mut self, data: &[u8; 16]) {
44        let aes = Aes256Enc::new_from_slice(self.secret.as_ref()).unwrap();
45        let mut encrypted = self.digest().0;
46
47        aes.encrypt_padded::<NoPadding>(&mut encrypted, B128::len_bytes()).unwrap();
48        for i in 0..data.len() {
49            encrypted[i] ^= data[i];
50        }
51        self.hasher.update(encrypted);
52    }
53
54    /// Accumulate the given message body into the MAC's internal state.
55    pub fn update_body(&mut self, data: &[u8]) {
56        self.hasher.update(data);
57        let prev = self.digest();
58        let aes = Aes256Enc::new_from_slice(self.secret.as_ref()).unwrap();
59        let mut encrypted = prev.0;
60
61        aes.encrypt_padded::<NoPadding>(&mut encrypted, B128::len_bytes()).unwrap();
62        for i in 0..16 {
63            encrypted[i] ^= prev[i];
64        }
65        self.hasher.update(encrypted);
66    }
67
68    /// Produce a digest by finalizing the internal keccak256 hasher and returning the first 128
69    /// bits.
70    pub fn digest(&self) -> B128 {
71        B128::from_slice(&self.hasher.clone().finalize()[..16])
72    }
73}
reth_ecies/mac.rs

reth_ecies/
mac.rs
