Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Correctly clamp Curve25519 secret keys #323

Merged
merged 1 commit into from
May 22, 2023
Merged

Correctly clamp Curve25519 secret keys #323

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
3 changes: 1 addition & 2 deletions Cargo.toml
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ version = "3.0.0-pre.2"

[features]
argon2 = ["dep:argon2"]
curve25519 = ["dep:curve25519-dalek", "curve25519-dalek?/precomputed-tables"]
curve25519 = ["dep:curve25519-dalek"]
default = ["ristretto255-voprf", "serde"]
ristretto255 = ["dep:curve25519-dalek", "voprf/ristretto255"]
ristretto255-voprf = ["ristretto255", "voprf/ristretto255-ciphersuite"]
Expand All @@ -25,7 +25,6 @@ argon2 = { version = "0.5", default-features = false, features = [
"alloc",
], optional = true }
curve25519-dalek = { version = "=4.0.0-rc.2", default-features = false, features = [
"rand_core",
"zeroize",
], optional = true }
derive-where = { version = "1", features = ["zeroize-on-drop"] }
Expand Down
15 changes: 11 additions & 4 deletions src/key_exchange/group/curve25519.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@

//! Key Exchange group implementation for Curve25519

use curve25519_dalek::constants::ED25519_BASEPOINT_TABLE;
use curve25519_dalek::constants::X25519_BASEPOINT;
use curve25519_dalek::montgomery::MontgomeryPoint;
use curve25519_dalek::scalar::Scalar;
use curve25519_dalek::traits::Identity;
Expand Down Expand Up @@ -47,7 +47,10 @@ impl KeGroup for Curve25519 {

fn random_sk<R: RngCore + CryptoRng>(rng: &mut R) -> Self::Sk {
loop {
let scalar = Scalar::random(rng);
// Sample 32 random bytes and then clamp, as described in https://cr.yp.to/ecdh.html
let mut scalar_bytes = [0u8; 32];
rng.fill_bytes(&mut scalar_bytes);
let scalar = Scalar::from_bits_clamped(scalar_bytes);

if scalar != Scalar::ZERO {
break scalar;
Expand All @@ -68,6 +71,7 @@ impl KeGroup for Curve25519 {
.fill_bytes(&mut uniform_bytes);

let scalar = Scalar::from_bytes_mod_order_wide(&uniform_bytes.into());
let scalar = Scalar::from_bits_clamped(scalar.to_bytes());

if scalar == Scalar::ZERO {
Err(InternalError::HashToScalar)
Expand All @@ -81,7 +85,7 @@ impl KeGroup for Curve25519 {
}

fn public_key(sk: Self::Sk) -> Self::Pk {
(ED25519_BASEPOINT_TABLE * &sk).to_montgomery()
X25519_BASEPOINT * sk
}

fn diffie_hellman(pk: Self::Pk, sk: Self::Sk) -> GenericArray<u8, Self::PkLen> {
Expand All @@ -96,7 +100,10 @@ impl KeGroup for Curve25519 {
bytes
.try_into()
.ok()
.and_then(|bytes| Scalar::from_canonical_bytes(bytes).into())
.and_then(|bytes| {
let scalar = Scalar::from_bits_clamped(bytes);
(scalar.as_bytes() == &bytes).then_some(scalar)
})
.filter(|scalar| scalar != &Scalar::ZERO)
.ok_or(InternalError::PointError)
}
Expand Down
Loading