Function hmac_sha256

rust/stringzilla.rs:625–654

Computes HMAC-SHA256 (Hash-based Message Authentication Code) for the given key and message. # Arguments `key` - The secret key (can be any length, will be hashed if > 64 bytes) `message` - The message to authenticate # Returns A 32-byte HMAC-SHA256 digest # Example ``` use stringzilla::stringzilla::hmac_sha256; let key = b"secret_key"; let message = b"important message"; let mac = hmac_sha2

(key: &[u8], message: &[u8])

/// assert_eq!(mac.len(), 32);
/// ```
pub fn hmac_sha256(key: &[u8], message: &[u8]) -> [u8; 32] {
    // Prepare key: hash if > 64 bytes, zero-pad to 64 bytes
    let mut key_pad = [0u8; 64];
    if key.len() > 64 {
        let key_hash = Sha256::hash(key);
        key_pad[..32].copy_from_slice(&key_hash);
    } else {
        key_pad[..key.len()].copy_from_slice(key);
    }

    // Compute inner hash: SHA256((key ^ 0x36) || message)
    let mut inner_hasher = Sha256::new();
    let mut inner_pad = [0u8; 64];
    for i in 0..64 {
        inner_pad[i] = key_pad[i] ^ 0x36;
    }
    inner_hasher.update(&inner_pad);
    inner_hasher.update(message);
    let inner_hash = inner_hasher.digest();

    // Compute outer hash: SHA256((key ^ 0x5c) || inner_hash)
    let mut outer_hasher = Sha256::new();
    let mut outer_pad = [0u8; 64];
    for i in 0..64 {
        outer_pad[i] = key_pad[i] ^ 0x5c;
    }
    outer_hasher.update(&outer_pad);
    outer_hasher.update(&inner_hash);
    outer_hasher.digest()
}

/// Standard Hasher trait to interoperate with `std::collections`.
impl core::hash::Hasher for Hasher {