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use crate::anchor::AnchorSet;
use crate::bls::{BlsKeypair, BlsPubkey, BlsSig};
use crate::error::{Error, check, check_ssize};
use crate::ffi;
use crate::types::{MerkleHash, Tstamp};
/// `CHECKPOINT_MESSAGE_SIZE` is the byte length of the canonical message that anchors sign.
///
/// The message is `epoch (8) + timestamp (8) + merkle_root (32) + log_size (8) = 56` bytes.
pub const CHECKPOINT_MESSAGE_SIZE: usize = 56;
/// `Checkpoint` is a BLS-signed snapshot of the Merkle log at a given epoch.
///
/// `Checkpoint` records the Merkle root, log size, and the aggregate BLS signature
/// from anchor nodes that attested to this state. Use [`Checkpoint::verify`] to
/// confirm that a quorum of trusted anchors signed the checkpoint before trusting
/// any identity proofs that reference it.
#[derive(Clone, Debug)]
pub struct Checkpoint {
/// Monotonically increasing checkpoint sequence number.
pub epoch: u64,
/// Unix timestamp (nanoseconds) when the checkpoint was created.
pub timestamp: Tstamp,
/// Merkle root hash of the log at this checkpoint.
pub merkle_root: MerkleHash,
/// Number of entries in the log at this checkpoint.
pub log_size: u64,
/// Aggregated BLS signature from all signing anchor nodes.
pub signature: BlsSig,
/// BLS public keys of the anchors that contributed to `signature`.
pub signers: Vec<BlsPubkey>,
}
impl Checkpoint {
/// `new` creates an unsigned checkpoint for the given log state.
///
/// After creation, each anchor in the quorum must call [`sign`](Checkpoint::sign)
/// to add its BLS signature before the checkpoint can be verified.
///
/// # Errors
///
/// Returns `Err` if the C library call fails (e.g. invalid parameters).
pub fn new(
epoch: u64,
timestamp: Tstamp,
merkle_root: MerkleHash,
log_size: u64,
) -> Result<Self, Error> {
let mut cp = unsafe { std::mem::zeroed::<ffi::nwep_checkpoint>() };
let ffi_root = ffi::nwep_merkle_hash {
data: merkle_root.0,
};
check(unsafe { ffi::nwep_checkpoint_new(&mut cp, epoch, timestamp, &ffi_root, log_size) })?;
Ok(Checkpoint::from_ffi(&cp))
}
/// `sign` adds this anchor's BLS signature to the checkpoint.
///
/// Multiple anchors may call `sign` independently; the resulting signatures are
/// aggregated by the C library. Once enough anchors have signed, [`verify`](Checkpoint::verify)
/// will succeed against the corresponding [`AnchorSet`].
///
/// # Errors
///
/// Returns `Err` if signing fails (e.g. invalid keypair or message).
pub fn sign(&mut self, anchor_kp: &BlsKeypair) -> Result<(), Error> {
let mut ffi_cp = self.to_ffi();
check(unsafe { ffi::nwep_checkpoint_sign(&mut ffi_cp, anchor_kp.as_ffi()) })?;
*self = Checkpoint::from_ffi(&ffi_cp);
Ok(())
}
/// `verify` checks that a quorum of anchors from `anchor_set` have signed this checkpoint.
///
/// Confirms that the aggregate BLS signature in `self.signature` is a valid signature
/// by at least `anchor_set.threshold()` of the registered anchor keys over the canonical
/// checkpoint message (epoch + timestamp + merkle_root + log_size).
///
/// # Errors
///
/// Returns `Err` if the signature is invalid, insufficient signers, or a C error occurs.
pub fn verify(&self, anchor_set: &AnchorSet) -> Result<(), Error> {
let ffi_cp = self.to_ffi();
check(unsafe { ffi::nwep_checkpoint_verify(&ffi_cp, anchor_set.as_ptr()) })
}
/// `encode` serializes the checkpoint to a byte vector for storage or transmission.
///
/// # Errors
///
/// Returns `Err` if serialization fails.
pub fn encode(&self) -> Result<Vec<u8>, Error> {
let ffi_cp = self.to_ffi();
let mut buf = vec![0u8; 4096];
let n = check_ssize(unsafe {
ffi::nwep_checkpoint_encode(buf.as_mut_ptr(), buf.len(), &ffi_cp)
})?;
buf.truncate(n);
Ok(buf)
}
/// `decode` deserializes a checkpoint from bytes produced by [`encode`](Checkpoint::encode).
///
/// # Errors
///
/// Returns `Err` if `data` is truncated or malformed.
pub fn decode(data: &[u8]) -> Result<Self, Error> {
let mut cp = unsafe { std::mem::zeroed::<ffi::nwep_checkpoint>() };
check(unsafe { ffi::nwep_checkpoint_decode(&mut cp, data.as_ptr(), data.len()) })?;
Ok(Checkpoint::from_ffi(&cp))
}
/// `message` returns the canonical [`CHECKPOINT_MESSAGE_SIZE`]-byte byte string that anchors sign.
///
/// The message is the concatenation of epoch, timestamp, merkle_root, and log_size,
/// all in big-endian byte order. This is the exact byte string passed to BLS signing.
///
/// # Errors
///
/// Returns `Err` if the C library call fails.
pub fn message(&self) -> Result<Vec<u8>, Error> {
let ffi_cp = self.to_ffi();
let mut buf = vec![0u8; 64];
let n = check_ssize(unsafe {
ffi::nwep_checkpoint_message(buf.as_mut_ptr(), buf.len(), &ffi_cp)
})?;
buf.truncate(n);
Ok(buf)
}
pub(crate) fn to_ffi(&self) -> ffi::nwep_checkpoint {
let mut cp = unsafe { std::mem::zeroed::<ffi::nwep_checkpoint>() };
cp.epoch = self.epoch;
cp.timestamp = self.timestamp;
cp.merkle_root = ffi::nwep_merkle_hash {
data: self.merkle_root.0,
};
cp.log_size = self.log_size;
cp.signature = ffi::nwep_bls_sig {
data: self.signature.0,
};
cp.num_signers = self.signers.len().min(crate::types::MAX_ANCHORS);
for (i, s) in self
.signers
.iter()
.take(crate::types::MAX_ANCHORS)
.enumerate()
{
cp.signers[i] = ffi::nwep_bls_pubkey { data: s.0 };
}
cp
}
pub(crate) fn from_ffi(cp: &ffi::nwep_checkpoint) -> Self {
let signers = (0..cp.num_signers)
.map(|i| BlsPubkey(cp.signers[i].data))
.collect();
Checkpoint {
epoch: cp.epoch,
timestamp: cp.timestamp,
merkle_root: MerkleHash(cp.merkle_root.data),
log_size: cp.log_size,
signature: BlsSig(cp.signature.data),
signers,
}
}
}