mirror of https://github.com/poanetwork/hbbft.git
254 lines
9.3 KiB
Rust
254 lines
9.3 KiB
Rust
//! # Collaborative Threshold Decryption
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//!
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//! Each node inputs the same encrypted data, and after at least _f + 1_ correct validators have
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//! done so, each node outputs the decrypted data.
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//!
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//! ## How it works
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//!
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//! The algorithm uses a threshold encryption scheme: A message encrypted to the network's public
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//! key can be collaboratively decrypted by combining at least _f + 1_ decryption shares. Each
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//! validator holds a secret key share, and uses it to produce and multicast a decryption share once
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//! a ciphertext is provided. The algorithm outputs as soon as it receives a ciphertext and _f + 1_
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//! threshold shares.
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use std::collections::BTreeMap;
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use std::sync::Arc;
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use crate::crypto::{self, Ciphertext, DecryptionShare};
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use failure::Fail;
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use rand::Rng;
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use rand_derive::Rand;
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use serde::{Deserialize, Serialize};
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use crate::fault_log::{self, Fault};
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use crate::{ConsensusProtocol, NetworkInfo, NodeIdT, Target};
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/// A threshold decryption error.
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#[derive(Clone, Eq, PartialEq, Debug, Fail)]
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pub enum Error {
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/// Redundant input provided.
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#[fail(display = "Redundant input provided: {:?}", _0)]
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MultipleInputs(Box<Ciphertext>),
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/// Invalid ciphertext.
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#[fail(display = "Invalid ciphertext: {:?}", _0)]
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InvalidCiphertext(Box<Ciphertext>),
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/// Unknown sender.
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#[fail(display = "Unknown sender")]
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UnknownSender,
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/// Decryption failed.
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#[fail(display = "Decryption failed: {:?}", _0)]
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Decryption(crypto::error::Error),
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/// Tried to decrypt before setting a cipherext.
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#[fail(display = "Tried to decrypt before setting ciphertext")]
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CiphertextIsNone,
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}
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/// A threshold decryption result.
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pub type Result<T> = ::std::result::Result<T, Error>;
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/// A threshold decryption message fault
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#[derive(Clone, Debug, Fail, PartialEq)]
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pub enum FaultKind {
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/// `ThresholdDecrypt` received multiple shares from the same sender.
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#[fail(display = "`ThresholdDecrypt` received multiple shares from the same sender.")]
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MultipleDecryptionShares,
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/// `HoneyBadger` received a decryption share from an unverified sender.
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#[fail(display = "`HoneyBadger` received a decryption share from an unverified sender.")]
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UnverifiedDecryptionShareSender,
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}
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/// The type of fault log whose entries are `ThresholdDecrypt` faults.
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pub type FaultLog<N> = fault_log::FaultLog<N, FaultKind>;
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/// A Threshold Decryption message.
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#[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Rand)]
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pub struct Message(pub DecryptionShare);
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/// A Threshold Decrypt algorithm instance. If every node inputs the same data, encrypted to the
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/// network's public key, every node will output the decrypted data.
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#[derive(Debug)]
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pub struct ThresholdDecrypt<N> {
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netinfo: Arc<NetworkInfo<N>>,
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/// The encrypted data.
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ciphertext: Option<Ciphertext>,
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/// All received threshold decryption shares.
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shares: BTreeMap<N, (usize, DecryptionShare)>,
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/// Whether we already sent our shares.
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had_input: bool,
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/// Whether we have already returned the output.
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terminated: bool,
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}
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/// A `ThresholdDecrypt` step. It will contain at most one output.
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pub type Step<N> = crate::CpStep<ThresholdDecrypt<N>>;
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impl<N: NodeIdT> ConsensusProtocol for ThresholdDecrypt<N> {
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type NodeId = N;
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type Input = ();
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type Output = Vec<u8>;
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type Message = Message;
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type Error = Error;
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type FaultKind = FaultKind;
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fn handle_input<R: Rng>(&mut self, _input: (), _rng: &mut R) -> Result<Step<N>> {
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self.start_decryption()
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}
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fn handle_message<R: Rng>(
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&mut self,
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sender_id: &Self::NodeId,
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message: Message,
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_rng: &mut R,
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) -> Result<Step<N>> {
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self.handle_message(sender_id, message)
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}
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fn terminated(&self) -> bool {
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self.terminated
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}
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fn our_id(&self) -> &N {
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self.netinfo.our_id()
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}
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}
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impl<N: NodeIdT> ThresholdDecrypt<N> {
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/// Creates a new Threshold Decrypt instance.
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pub fn new(netinfo: Arc<NetworkInfo<N>>) -> Self {
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ThresholdDecrypt {
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netinfo,
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ciphertext: None,
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shares: BTreeMap::new(),
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had_input: false,
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terminated: false,
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}
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}
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/// Creates a new instance of `ThresholdDecrypt`, including setting the ciphertext to
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/// decrypt.
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pub fn new_with_ciphertext(netinfo: Arc<NetworkInfo<N>>, ct: Ciphertext) -> Result<Self> {
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let mut td = ThresholdDecrypt::new(netinfo);
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td.set_ciphertext(ct)?;
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Ok(td)
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}
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/// Sets the ciphertext, sends the decryption share, and tries to decrypt it.
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/// This must be called exactly once, with the same ciphertext in all participating nodes.
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/// If we have enough shares, outputs the plaintext.
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pub fn set_ciphertext(&mut self, ct: Ciphertext) -> Result<()> {
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if self.ciphertext.is_some() {
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return Err(Error::MultipleInputs(Box::new(ct)));
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}
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if !ct.verify() {
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return Err(Error::InvalidCiphertext(Box::new(ct)));
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}
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self.ciphertext = Some(ct);
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Ok(())
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}
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/// Sends our decryption shares to peers, and if we have collected enough, returns the decrypted
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/// message. Returns an error if the ciphertext hasn't been received yet.
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pub fn start_decryption(&mut self) -> Result<Step<N>> {
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if self.had_input {
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return Ok(Step::default()); // Don't waste time on redundant shares.
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}
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let ct = self.ciphertext.clone().ok_or(Error::CiphertextIsNone)?;
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let mut step = Step::default();
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step.fault_log.extend(self.remove_invalid_shares());
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self.had_input = true;
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let opt_idx = self.netinfo.node_index(self.our_id());
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let (idx, share) = match (opt_idx, self.netinfo.secret_key_share()) {
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(Some(idx), Some(sks)) => (idx, sks.decrypt_share_no_verify(&ct)),
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(_, _) => return Ok(step.join(self.try_output()?)), // Not a validator.
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};
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let our_id = self.our_id().clone();
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let msg = Target::all().message(Message(share.clone()));
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step.messages.push(msg);
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self.shares.insert(our_id, (idx, share));
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step.extend(self.try_output()?);
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Ok(step)
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}
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/// Returns an iterator over the IDs of all nodes who sent a share.
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pub fn sender_ids(&self) -> impl Iterator<Item = &N> {
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self.shares.keys()
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}
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/// Handles a message with a decryption share received from `sender_id`.
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///
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/// This must be called with every message we receive from another node.
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///
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/// If we have collected enough, returns the decrypted message.
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pub fn handle_message(&mut self, sender_id: &N, message: Message) -> Result<Step<N>> {
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if self.terminated {
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return Ok(Step::default()); // Don't waste time on redundant shares.
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}
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// Before checking the share, ensure the sender is a known validator
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let idx = self
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.netinfo
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.node_index(sender_id)
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.ok_or(Error::UnknownSender)?;
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let Message(share) = message;
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if !self.is_share_valid(sender_id, &share) {
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let fault_kind = FaultKind::UnverifiedDecryptionShareSender;
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return Ok(Fault::new(sender_id.clone(), fault_kind).into());
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}
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let entry = (idx, share);
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if self.shares.insert(sender_id.clone(), entry).is_some() {
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return Ok(Fault::new(sender_id.clone(), FaultKind::MultipleDecryptionShares).into());
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}
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self.try_output()
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}
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/// Removes all shares that are invalid, and returns faults for their senders.
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fn remove_invalid_shares(&mut self) -> FaultLog<N> {
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let faulty_senders: Vec<N> = self
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.shares
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.iter()
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.filter(|(id, (_, share))| !self.is_share_valid(id, share))
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.map(|(id, _)| id.clone())
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.collect();
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let mut fault_log = FaultLog::default();
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for id in faulty_senders {
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self.shares.remove(&id);
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fault_log.append(id, FaultKind::UnverifiedDecryptionShareSender);
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}
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fault_log
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}
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/// Returns `true` if the share is valid, or if we don't have the ciphertext yet.
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fn is_share_valid(&self, id: &N, share: &DecryptionShare) -> bool {
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let ct = match self.ciphertext {
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None => return true, // No ciphertext yet. Verification postponed.
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Some(ref ct) => ct,
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};
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match self.netinfo.public_key_share(id) {
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None => false, // Unknown sender.
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Some(pk) => pk.verify_decryption_share(share, ct),
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}
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}
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/// Outputs the decrypted message, if we have the ciphertext and enough shares.
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fn try_output(&mut self) -> Result<Step<N>> {
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if self.terminated || self.shares.len() <= self.netinfo.num_faulty() {
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return Ok(Step::default()); // Not enough shares yet, or already terminated.
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}
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let ct = match self.ciphertext {
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None => return Ok(Step::default()), // Still waiting for the ciphertext.
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Some(ref ct) => ct.clone(),
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};
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self.terminated = true;
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let step = self.start_decryption()?; // Before terminating, make sure we sent our share.
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let share_itr = self
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.shares
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.values()
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.map(|&(ref idx, ref share)| (idx, share));
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let plaintext = self
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.netinfo
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.public_key_set()
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.decrypt(share_itr, &ct)
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.map_err(Error::Decryption)?;
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Ok(step.with_output(plaintext))
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}
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}
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