Summary
HMAC signature comparison is not timing-safe and is vulnerable to timing attacks.
Details
SharedKey::sign() returns a Vec<u8> which has a non-constant-time equality implementation.
Hmac::finalize() returns a constant-time wrapper (CtOutput) which was discarded. Alternatively, Hmac has a constant-time verify() method.
The problem reported here is due to the following lines in SharedKey::sign() of the previous code:
let mut mac = HmacSha256::new_from_slice(key).unwrap();
mac.update(data);
Ok(mac.finalize().into_bytes().to_vec())
and the merged update changes the third line to directly verify with verify_slice.
Impact
Anyone who uses HS256 signature verification is vulnerably to Timing Attack that allows the attacker to forge a signature.
Summary
HMAC signature comparison is not timing-safe and is vulnerable to timing attacks.
Details
SharedKey::sign()returns aVec<u8>which has a non-constant-time equality implementation.Hmac::finalize()returns a constant-time wrapper (CtOutput) which was discarded. Alternatively,Hmachas a constant-timeverify()method.The problem reported here is due to the following lines in
SharedKey::sign()of the previous code:and the merged update changes the third line to directly verify with
verify_slice.Impact
Anyone who uses HS256 signature verification is vulnerably to Timing Attack that allows the attacker to forge a signature.