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Introduce a constant for the length of the output of hs_mac()

This commit is contained in:
Nick Mathewson 2023-03-01 11:26:35 -05:00
parent b36082255b
commit 5131703c22
2 changed files with 8 additions and 5 deletions
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6
crates/tor-cell/src/relaycell/hs/est_intro.rs
View File

@ -3,7 +3,7 @@
use caret::caret_int;
use tor_bytes::{EncodeError, EncodeResult, Readable, Reader, Result, Writeable, Writer};
use tor_error::bad_api_usage;
use tor_hscrypto::ops::hs_mac;
use tor_hscrypto::ops::{hs_mac, HS_MAC_LEN};
use tor_llcrypto::{
pk::ed25519::{self, Ed25519Identity, ED25519_ID_LEN, ED25519_SIGNATURE_LEN},
util::ct::CtByteArray,
@ -165,7 +165,7 @@ pub struct EstablishIntro {
///
/// This MAC binds the EstablishIntro message to a single circuit, and keeps
/// it from being replayed.
handshake_auth: CtByteArray<32>,
handshake_auth: CtByteArray<HS_MAC_LEN>,
/// A textual record of all the fields in the
#[educe(Debug(ignore))]
mac_plaintext: Vec<u8>,
@ -332,7 +332,7 @@ impl EstablishIntro {
#[cfg(feature = "testing")]
pub fn from_parts_for_test(
body: EstablishIntroDetails,
mac: CtByteArray<32>,
mac: CtByteArray<HS_MAC_LEN>,
signature: ed25519::Signature,
) -> Self {
use tor_llcrypto::pk::ed25519::ValidatableEd25519Signature;

7
crates/tor-hscrypto/src/ops.rs
View File

@ -5,10 +5,13 @@ use tor_llcrypto::util::ct::CtByteArray;
use digest::Digest;
/// The length of the MAC returned by [`hs_mac`].
pub const HS_MAC_LEN: usize = 32;
/// Compute the lightweight MAC function used in the onion service protocol.
///
/// (rend-spec-v3 section 0.3 `MAC`)
pub fn hs_mac(key: &[u8], msg: &[u8]) -> CtByteArray<32> {
pub fn hs_mac(key: &[u8], msg: &[u8]) -> CtByteArray<HS_MAC_LEN> {
// rend-spec-v3 says: "Instantiate H with SHA3-256... Instantiate MAC(key=k,
// message=m) with H(k_len | k | m), where k_len is htonll(len(k))."
@ -17,7 +20,7 @@ pub fn hs_mac(key: &[u8], msg: &[u8]) -> CtByteArray<32> {
hasher.update(klen.to_be_bytes());
hasher.update(key);
hasher.update(msg);
let a: [u8; 32] = hasher.finalize().into();
let a: [u8; HS_MAC_LEN] = hasher.finalize().into();
a.into()
}