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Further hardened delta #796

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merged 1 commit into from
Aug 8, 2024
+42 −26
Merged

Further hardened delta #796

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3 changes: 0 additions & 3 deletions chain-signatures/node/src/indexer.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
use crate::gcp::error::DatastoreStorageError;
use crate::gcp::GcpService;
use crate::kdf;
use crate::protocol::{SignQueue, SignRequest};
use crate::types::LatestBlockHeight;
use crypto_shared::{derive_epsilon, ScalarExt};
Expand Down Expand Up @@ -213,7 +212,6 @@ async fn handle_block(
continue;
};
let epsilon = derive_epsilon(&action.predecessor_id(), &arguments.request.path);
let delta = kdf::derive_delta(receipt_id, entropy);
tracing::info!(
receipt_id = %receipt_id,
caller_id = receipt.predecessor_id().to_string(),
Expand All @@ -232,7 +230,6 @@ async fn handle_block(
receipt_id,
request,
epsilon,
delta,
entropy,
// TODO: use indexer timestamp instead.
time_added: Instant::now(),
Expand Down
17 changes: 13 additions & 4 deletions chain-signatures/node/src/kdf.rs
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Original file line number Diff line number Diff line change
@@ -1,18 +1,27 @@
use anyhow::Context;
use crypto_shared::{kdf::recover, x_coordinate, ScalarExt, SignatureResponse};
use hkdf::Hkdf;
use k256::{ecdsa::RecoveryId, elliptic_curve::sec1::ToEncodedPoint, Scalar};
use k256::{ecdsa::RecoveryId, elliptic_curve::sec1::ToEncodedPoint, AffinePoint, Scalar};
use near_primitives::hash::CryptoHash;
use sha3::Sha3_256;

// In case there are multiple requests in the same block (hence same entropy), we need to ensure
// that we generate different random scalars as delta tweaks.
// Receipt ID should be unique inside of a block, so it serves us as the request identifier.
pub fn derive_delta(receipt_id: CryptoHash, entropy: [u8; 32]) -> Scalar {
pub fn derive_delta(
receipt_id: CryptoHash,
entropy: [u8; 32],
presignature_big_r: AffinePoint,
) -> Scalar {
let hk = Hkdf::<Sha3_256>::new(None, &entropy);
let info = format!("{DELTA_DERIVATION_PREFIX}:{}", receipt_id);
let mut okm = [0u8; 32];
hk.expand(info.as_bytes(), &mut okm).unwrap();
hk.expand(
presignature_big_r.to_encoded_point(true).as_bytes(),
&mut okm,
)
.unwrap();
Scalar::from_non_biased(okm)
}

Expand All @@ -31,7 +40,7 @@ pub fn into_eth_sig(
let signature = k256::ecdsa::Signature::from_scalars(x_coordinate(big_r), s)
.context("cannot create signature from cait_sith signature")?;
let pk0 = recover(
&msg_hash.to_bytes(),
&msg_hash.to_bytes()[..],
&signature,
RecoveryId::try_from(0).context("cannot create recovery_id=0")?,
)
Expand All @@ -42,7 +51,7 @@ pub fn into_eth_sig(
}

let pk1 = recover(
&msg_hash.to_bytes(),
&msg_hash.to_bytes()[..],
&signature,
RecoveryId::try_from(1).context("cannot create recovery_id=1")?,
)
Expand Down
6 changes: 3 additions & 3 deletions chain-signatures/node/src/protocol/message.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -68,7 +68,7 @@ pub struct SignatureMessage {
pub presignature_id: PresignatureId,
pub request: ContractSignRequest,
pub epsilon: Scalar,
pub delta: Scalar,
pub entropy: [u8; 32],
pub epoch: u64,
pub from: Participant,
pub data: MessageData,
Expand Down Expand Up @@ -387,7 +387,7 @@ impl MessageHandler for RunningState {
presignature_id,
request,
epsilon,
delta,
entropy,
..
} = queue.front().unwrap();

Expand Down Expand Up @@ -418,7 +418,7 @@ impl MessageHandler for RunningState {
*presignature_id,
request,
*epsilon,
*delta,
*entropy,
&mut presignature_manager,
protocol_cfg,
) {
Expand Down
42 changes: 26 additions & 16 deletions chain-signatures/node/src/protocol/signature.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,9 +2,10 @@ use super::contract::primitives::Participants;
use super::message::SignatureMessage;
use super::presignature::{GenerationError, Presignature, PresignatureId, PresignatureManager};
use crate::indexer::ContractSignRequest;
use crate::kdf::into_eth_sig;
use crate::kdf::{derive_delta, into_eth_sig};
use crate::types::SignatureProtocol;
use crate::util::AffinePointExt;
use near_primitives::hash::CryptoHash;

use cait_sith::protocol::{Action, InitializationError, Participant, ProtocolError};
use cait_sith::{FullSignature, PresignOutput};
Expand All @@ -30,7 +31,6 @@ pub struct SignRequest {
pub receipt_id: ReceiptId,
pub request: ContractSignRequest,
pub epsilon: Scalar,
pub delta: Scalar,
pub entropy: [u8; 32],
pub time_added: Instant,
}
Expand Down Expand Up @@ -162,7 +162,8 @@ pub struct SignatureGenerator {
pub presignature_id: PresignatureId,
pub request: ContractSignRequest,
pub epsilon: Scalar,
pub delta: Scalar,
pub receipt_id: CryptoHash,
pub entropy: [u8; 32],
pub sign_request_timestamp: Instant,
pub generator_timestamp: Instant,
pub timeout: Duration,
Expand All @@ -178,7 +179,8 @@ impl SignatureGenerator {
presignature_id: PresignatureId,
request: ContractSignRequest,
epsilon: Scalar,
delta: Scalar,
receipt_id: CryptoHash,
entropy: [u8; 32],
sign_request_timestamp: Instant,
cfg: &ProtocolConfig,
) -> Self {
Expand All @@ -189,7 +191,8 @@ impl SignatureGenerator {
presignature_id,
request,
epsilon,
delta,
receipt_id,
entropy,
sign_request_timestamp,
generator_timestamp: Instant::now(),
timeout: Duration::from_millis(cfg.signature.generation_timeout),
Expand Down Expand Up @@ -221,7 +224,8 @@ pub struct GenerationRequest {
pub proposer: Participant,
pub request: ContractSignRequest,
pub epsilon: Scalar,
pub delta: Scalar,
pub receipt_id: CryptoHash,
pub entropy: [u8; 32],
pub sign_request_timestamp: Instant,
}

Expand Down Expand Up @@ -302,10 +306,12 @@ impl SignatureManager {
proposer,
request,
epsilon,
delta,
receipt_id,
entropy,
sign_request_timestamp,
} = req;
let PresignOutput { big_r, k, sigma } = presignature.output;
let delta = derive_delta(receipt_id, entropy, big_r);
// TODO: Check whether it is okay to use invert_vartime instead
let output: PresignOutput<Secp256k1> = PresignOutput {
big_r: (big_r * delta).to_affine(),
Expand All @@ -330,7 +336,8 @@ impl SignatureManager {
presignature_id,
request,
epsilon,
delta,
receipt_id,
entropy,
sign_request_timestamp,
cfg,
))
Expand Down Expand Up @@ -368,7 +375,7 @@ impl SignatureManager {
presignature: Presignature,
request: ContractSignRequest,
epsilon: Scalar,
delta: Scalar,
entropy: [u8; 32],
sign_request_timestamp: Instant,
cfg: &ProtocolConfig,
) -> Result<(), (Presignature, InitializationError)> {
Expand All @@ -388,7 +395,8 @@ impl SignatureManager {
proposer: self.me,
request,
epsilon,
delta,
receipt_id,
entropy,
sign_request_timestamp,
},
cfg,
Expand All @@ -412,7 +420,7 @@ impl SignatureManager {
presignature_id: PresignatureId,
request: &ContractSignRequest,
epsilon: Scalar,
delta: Scalar,
entropy: [u8; 32],
presignature_manager: &mut PresignatureManager,
cfg: &ProtocolConfig,
) -> Result<&mut SignatureProtocol, GenerationError> {
Expand Down Expand Up @@ -449,7 +457,8 @@ impl SignatureManager {
proposer,
request: request.clone(),
epsilon,
delta,
entropy,
receipt_id,
sign_request_timestamp: Instant::now(),
},
cfg,
Expand Down Expand Up @@ -490,7 +499,8 @@ impl SignatureManager {
proposer: generator.proposer,
request: generator.request.clone(),
epsilon: generator.epsilon,
delta: generator.delta,
receipt_id: generator.receipt_id,
entropy: generator.entropy,
sign_request_timestamp: generator.sign_request_timestamp
},
));
Expand Down Expand Up @@ -518,7 +528,7 @@ impl SignatureManager {
presignature_id: generator.presignature_id,
request: generator.request.clone(),
epsilon: generator.epsilon,
delta: generator.delta,
entropy: generator.entropy,
epoch: self.epoch,
from: self.me,
data: data.clone(),
Expand All @@ -535,7 +545,7 @@ impl SignatureManager {
presignature_id: generator.presignature_id,
request: generator.request.clone(),
epsilon: generator.epsilon,
delta: generator.delta,
entropy: generator.entropy,
epoch: self.epoch,
from: self.me,
data,
Expand Down Expand Up @@ -641,7 +651,7 @@ impl SignatureManager {
presignature,
my_request.request,
my_request.epsilon,
my_request.delta,
my_request.entropy,
my_request.time_added,
cfg,
) {
Expand Down
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