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Ban zero ECDH keys, document non-zero requirements

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This commit is contained in:
Luke Parker
2024-07-28 01:35:11 -04:00
parent f93bd42b99
commit 681010f422
2 changed files with 23 additions and 3 deletions
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11
crypto/dkg/src/evrf/mod.rs
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@@ -208,6 +208,8 @@ pub enum EvrfError {
TooManyParticipants,
#[error("the threshold t wasn't in range 1 <= t <= n")]
InvalidThreshold,
#[error("a public key was the identity point")]
PublicKeyWasIdentity,
#[error("participating in a DKG we aren't a participant in")]
NotAParticipant,
#[error("a participant with an unrecognized ID participated")]
@@ -244,6 +246,8 @@ where
///
/// The context MUST be unique across invocations. Reuse of context will lead to sharing
/// prior-shared secrets.
///
/// Public keys are not allowed to be the identity point. This will error if any are.
pub fn participate(
rng: &mut (impl RngCore + CryptoRng),
generators: &EvrfGenerators<C>,
@@ -257,6 +261,9 @@ where
if (t == 0) || (t > n) {
Err(EvrfError::InvalidThreshold)?;
}
if evrf_public_keys.iter().any(|key| bool::from(key.is_identity())) {
Err(EvrfError::PublicKeyWasIdentity)?;
};
if !evrf_public_keys.iter().any(|key| *key == evrf_public_key) {
Err(EvrfError::NotAParticipant)?;
};
@@ -314,6 +321,9 @@ where
if (t == 0) || (t > n) {
Err(EvrfError::InvalidThreshold)?;
}
if evrf_public_keys.iter().any(|key| bool::from(key.is_identity())) {
Err(EvrfError::PublicKeyWasIdentity)?;
};
for i in participations.keys() {
if u16::from(*i) > n {
Err(EvrfError::NonExistentParticipant)?;
@@ -492,7 +502,6 @@ where
let mut ecdh = Zeroizing::new(C::F::ZERO);
for point in ecdh_keys {
// TODO: Explicitly ban 0-ECDH commitments, 0-eVRF public keys, and gen non-zero keys
let (mut x, mut y) =
<C::EmbeddedCurve as Ciphersuite>::G::to_xy(point * evrf_private_key.deref()).unwrap();
*ecdh += x;