lox_extensions/

lib.rs

/*! Implementation of a new style of bridge authority for Tor that
allows users to invite other users, while protecting the social graph
from the bridge authority itself.

We use uCMZ credentials (Orr`u, 2024 https://eprint.iacr.org/2024/1552.pdf) which improves issuer efficiency
over our original CMZ14 credential (GGM version, which is more efficient, but
makes a stronger security assumption) implementation: "Algebraic MACs and
Keyed-Verification Anonymous Credentials" (Chase, Meiklejohn, and
Zaverucha, CCS 2014)

The notation follows that of the paper "Hyphae: Social Secret Sharing"
(Lovecruft and de Valence, 2017), Section 4. */

// We want Scalars to be lowercase letters, and Points and credentials
// to be capital letters
#![allow(non_snake_case)]

#[cfg(feature = "bridgeauth")]
use ed25519_dalek::{Signature, SignatureError, Signer, SigningKey, Verifier, VerifyingKey};
use subtle::ConstantTimeEq;

#[cfg(feature = "bridgeauth")]
use chrono::{DateTime, Duration, Utc};
#[cfg(feature = "bridgeauth")]
use cmz::*;
use curve25519_dalek::ristretto::RistrettoPoint as G;
use group::Group;
#[cfg(feature = "bridgeauth")]
use rand::{rngs::OsRng, CryptoRng, Rng, RngCore};
#[cfg(feature = "bridgeauth")]
use std::collections::HashMap;
type Scalar = <G as Group>::Scalar;
#[cfg(feature = "bridgeauth")]
use sha2::Sha512;

pub mod bridge_table;
pub mod dup_filter;
pub mod lox_creds;
pub mod migration_table;
pub mod mock_auth;
pub mod proto {
    pub mod blockage_migration;
    pub mod check_blockage;
    pub mod errors;
    pub mod issue_invite;
    pub mod level_up;
    pub mod migration;
    pub mod open_invite;
    pub mod redeem_invite;
    pub mod trust_promotion;
    pub mod update_cred;
    pub mod update_invite;
}

#[cfg(feature = "bridgeauth")]
use bridge_table::{
    BridgeLine, BridgeTable, EncryptedBucket, MAX_BRIDGES_PER_BUCKET, MIN_BUCKET_REACHABILITY,
};
#[cfg(feature = "bridgeauth")]
use lox_creds::*;
#[cfg(feature = "bridgeauth")]
use migration_table::{MigrationTable, MigrationType};
#[cfg(feature = "bridgeauth")]
use serde::{Deserialize, Serialize};
#[cfg(feature = "bridgeauth")]
use std::collections::HashSet;
#[cfg(any(feature = "bridgeauth", test))]
use thiserror::Error;

// EXPIRY_DATE is set to EXPIRY_DATE days for open-entry and blocked buckets in order to match
// the expiry date for Lox credentials.This particular value (EXPIRY_DATE) is chosen because
// values that are 2^k − 1 make range proofs more efficient, but this can be changed to any value
pub const EXPIRY_DATE: u32 = 511;

/// ReplaceSuccess sends a signal to the lox-distributor to inform
/// whether or not a bridge was successfully replaced
#[derive(PartialEq, Eq)]
#[cfg(feature = "bridgeauth")]
pub enum ReplaceSuccess {
    NotFound = 0,
    NotReplaced = 1,
    Replaced = 2,
    Removed = 3,
}

/// This error is thrown if the number of buckets/keys in the bridge table
/// exceeds u32 MAX.It is unlikely this error will ever occur.
#[derive(Error, Debug)]
#[cfg(feature = "bridgeauth")]
pub enum NoAvailableIDError {
    #[error("Find key exhausted with no available index found!")]
    ExhaustedIndexer,
}

/// This error is thrown after the MAX_DAILY_BRIDGES threshold for bridges
/// distributed in a day has been reached
#[derive(Error, Debug)]
#[cfg(any(feature = "bridgeauth", test))]
pub enum OpenInvitationError {
    #[error("The maximum number of bridges has already been distributed today, please try again tomorrow!")]
    ExceededMaxBridges,

    #[error("There are no bridges available for open invitations.")]
    NoBridgesAvailable,
}

#[derive(Error, Debug)]
#[cfg(feature = "bridgeauth")]
pub enum BridgeTableError {
    #[error("The bucket corresponding to key {0} was not in the bridge table")]
    MissingBucket(u32),
}

/// Number of times a given invitation is ditributed
pub const OPENINV_K: u32 = 10;
/// TODO: Decide on maximum daily number of invitations to be distributed
pub const MAX_DAILY_BRIDGES: u32 = 100;

/// The BridgeDb. This will typically be a singleton object. The
/// BridgeDb's role is simply to issue signed "open invitations" to
/// people who are not yet part of the system.
#[derive(Debug, Serialize, Deserialize)]
#[cfg(feature = "bridgeauth")]
pub struct BridgeDb {
    /// The keypair for signing open invitations
    keypair: SigningKey,
    /// The public key for verifying open invitations
    pub pubkey: VerifyingKey,
    /// The set of open-invitation buckets
    openinv_buckets: HashSet<u32>,
    /// The set of open invitation buckets that have been distributed
    distributed_buckets: Vec<u32>,
    #[serde(skip)]
    today: DateTime<Utc>,
    pub current_k: u32,
    pub daily_bridges_distributed: u32,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
#[cfg(feature = "bridgeauth")]
pub struct OldKeyStore {
    //    /// Most recently outdated lox secret and private keys for verifying update_cred credentials
    priv_key: CMZPrivkey<G>,
    //    /// The public key for verifying update_cred credentials
    pub pub_key: CMZPubkey<G>,
}

#[derive(Debug, Default, Clone, Serialize, Deserialize)]
#[cfg(feature = "bridgeauth")]
pub struct OldKeys {
    /// Most recently outdated lox secret and private keys for verifying update_cred credentials
    lox_keys: Vec<OldKeyStore>,
    /// Most recently outdated open_invitation VerifyingKey for verifying update_openinv tokens
    bridgedb_key: Vec<VerifyingKey>,
    /// Most recently outdated invitation secret and private keys for verifying update_inv credentials
    invitation_keys: Vec<OldKeyStore>,
}

#[derive(Debug, Default, Clone, Serialize, Deserialize)]
#[cfg(feature = "bridgeauth")]
pub struct OldFilters {
    /// Most recently outdated lox id filter
    lox_filter: Vec<dup_filter::DupFilter<Scalar>>,
    /// Most recently outdated open invitation filter
    openinv_filter: Vec<dup_filter::DupFilter<Scalar>>,
    /// Most recently outdated invitation filter
    invitation_filter: Vec<dup_filter::DupFilter<Scalar>>,
}

/// An open invitation is a [u8; OPENINV_LENGTH] where the first 32
/// bytes are the serialization of a random Scalar (the invitation id),
/// the next 4 bytes are a little-endian bucket number, and the last
/// SIGNATURE_LENGTH bytes are the signature on the first 36 bytes.
pub const OPENINV_LENGTH: usize = 32 // the length of the random
                                     // invitation id (a Scalar)
    + 4 // the length of the u32 for the bucket number
    + ed25519_dalek::SIGNATURE_LENGTH; // the length of the signature

#[cfg(feature = "bridgeauth")]
impl Default for BridgeDb {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(feature = "bridgeauth")]
impl BridgeDb {
    /// Create the BridgeDb.
    pub fn new() -> Self {
        let mut csprng = OsRng {};
        let keypair = SigningKey::generate(&mut csprng);
        let pubkey = keypair.verifying_key();
        Self {
            keypair,
            pubkey,
            openinv_buckets: Default::default(),
            distributed_buckets: Default::default(),
            today: Utc::now(),
            current_k: 0,
            daily_bridges_distributed: 0,
        }
    }

    pub fn openinv_length(&mut self) -> usize {
        self.openinv_buckets.len()
    }

    /// Rotate Open Invitation keys
    pub fn rotate_open_inv_keys(&mut self) -> VerifyingKey {
        let mut csprng = OsRng {};
        self.keypair = SigningKey::generate(&mut csprng);
        self.pubkey = self.keypair.verifying_key();
        self.pubkey
    }

    /// Insert an open-invitation bucket into the set
    pub fn insert_openinv(&mut self, bucket: u32) {
        self.openinv_buckets.insert(bucket);
    }

    /// Remove an open-invitation bucket from the set
    pub fn remove_openinv(&mut self, bucket: &u32) {
        self.openinv_buckets.remove(bucket);
    }

    /// Remove open invitation and/or otherwise distributed buckets that have
    /// become blocked or are expired to free up the index for a new bucket
    pub fn remove_blocked_or_expired_buckets(&mut self, bucket: &u32) {
        if self.openinv_buckets.contains(bucket) {
            println!("Removing a bucket that has not been distributed yet!");
            self.openinv_buckets.remove(bucket);
        } else if self.distributed_buckets.contains(bucket) {
            self.distributed_buckets.retain(|&x| x != *bucket);
        }
    }

    /// Mark a bucket as distributed
    pub fn mark_distributed(&mut self, bucket: u32) {
        self.distributed_buckets.push(bucket);
    }

    /// Produce an open invitation such that the next k users, where k is <
    /// OPENINV_K, will receive the same open invitation bucket
    /// chosen randomly from the set of open-invitation buckets.
    pub fn invite(&mut self) -> Result<[u8; OPENINV_LENGTH], OpenInvitationError> {
        let mut res: [u8; OPENINV_LENGTH] = [0; OPENINV_LENGTH];
        let mut rng = rand::rngs::OsRng;
        // Choose a random invitation id (a Scalar) and serialize it
        let id = Scalar::random(&mut rng);
        res[0..32].copy_from_slice(&id.to_bytes());
        let bucket_num: u32;
        if Utc::now() >= (self.today + Duration::days(1)) {
            self.today = Utc::now();
            self.daily_bridges_distributed = 0;
        }
        if self.daily_bridges_distributed < MAX_DAILY_BRIDGES {
            if self.current_k < OPENINV_K && !self.distributed_buckets.is_empty() {
                bucket_num = *self.distributed_buckets.last().unwrap();
                self.current_k += 1;
            } else {
                if self.openinv_buckets.is_empty() {
                    return Err(OpenInvitationError::NoBridgesAvailable);
                }
                // Choose a random bucket number (from the set of open
                // invitation buckets) and serialize it
                let openinv_vec: Vec<&u32> = self.openinv_buckets.iter().collect();
                bucket_num = *openinv_vec[rng.gen_range(0..openinv_vec.len())];
                self.mark_distributed(bucket_num);
                self.remove_openinv(&bucket_num);
                self.current_k = 1;
                self.daily_bridges_distributed += 1;
            }
            res[32..(32 + 4)].copy_from_slice(&bucket_num.to_le_bytes());
            // Sign the first 36 bytes and serialize it
            let sig = self.keypair.sign(&res[0..(32 + 4)]);
            res[(32 + 4)..].copy_from_slice(&sig.to_bytes());
            Ok(res)
        } else {
            Err(OpenInvitationError::ExceededMaxBridges)
        }
    }

    /// Verify an open invitation. Returns the invitation id and the
    /// bucket number if the signature checked out. It is up to the
    /// caller to then check that the invitation id has not been used
    /// before.
    pub fn verify(
        invitation: [u8; OPENINV_LENGTH],
        pubkey: VerifyingKey,
    ) -> Result<(Scalar, u32), SignatureError> {
        // Pull out the signature and verify it
        let sig = Signature::try_from(&invitation[(32 + 4)..])?;
        pubkey.verify(&invitation[0..(32 + 4)], &sig)?;
        // The signature passed. Pull out the bucket number and then
        // the invitation id
        let bucket = u32::from_le_bytes(invitation[32..(32 + 4)].try_into().unwrap());
        let s = Scalar::from_canonical_bytes(invitation[0..32].try_into().unwrap());
        if s.is_some().into() {
            Ok((s.unwrap(), bucket))
        } else {
            // It should never happen that there's a valid signature on
            // an invalid serialization of a Scalar, but check anyway.
            Err(SignatureError::new())
        }
    }

    /// For testing only: manually advance the day by the        given number
    /// of days
    pub fn advance_days(&mut self, days: u16) {
        if days > 0 {
            self.today += Duration::days(days.into()); // Reset daily bridges distributed count
            self.daily_bridges_distributed = 0;
        }
    }
}

/// The bridge authority. This will typically be a singleton object.
#[cfg(feature = "bridgeauth")]
#[derive(Default, Debug, Serialize, Deserialize)]
pub struct BridgeAuth {
    /// The private key for the main Lox credential
    lox_priv: CMZPrivkey<G>,
    /// The public key for the main Lox credential
    pub lox_pub: CMZPubkey<G>,
    /// The private key for migration credentials
    migration_priv: CMZPrivkey<G>,
    /// The public key for migration credentials
    pub migration_pub: CMZPubkey<G>,
    /// The private key for migration key credentials
    migrationkey_priv: CMZPrivkey<G>,
    /// The public key for migration key credentials
    pub migrationkey_pub: CMZPubkey<G>,
    /// The private key for bucket reachability credentials
    reachability_priv: CMZPrivkey<G>,
    /// The public key for bucket reachability credentials
    pub reachability_pub: CMZPubkey<G>,
    /// The private key for invitation credentials
    invitation_priv: CMZPrivkey<G>,
    /// The public key for invitation credentials
    pub invitation_pub: CMZPubkey<G>,

    /// The public key of the BridgeDb issuing open invitations
    pub bridgedb_pub: VerifyingKey,

    /// The bridge table
    bridge_table: BridgeTable,

    // Map of bridge fingerprint to values needed to verify TP reports
    //pub tp_bridge_infos: HashMap<String, BridgeVerificationInfo>,
    /// The migration tables
    trustup_migration_table: MigrationTable,
    blockage_migration_table: MigrationTable,

    /// Duplicate filter for open invitations
    bridgedb_pub_filter: dup_filter::DupFilter<Scalar>,
    /// Duplicate filter for Lox credential ids
    id_filter: dup_filter::DupFilter<Scalar>,
    /// Duplicate filter for Invitation credential ids
    inv_id_filter: dup_filter::DupFilter<Scalar>,
    /// Duplicate filter for trust promotions (from untrusted level 0 to
    /// trusted level 1)
    trust_promotion_filter: dup_filter::DupFilter<Scalar>,
    // Outdated Lox Keys to be populated with the old Lox private and public keys
    // after a key rotation
    old_keys: OldKeys,
    old_filters: OldFilters,

    /// For testing only: offset of the true time to the simulated time
    #[serde(skip)]
    time_offset: time::Duration,
}

#[cfg(feature = "bridgeauth")]
impl BridgeAuth {
    pub fn new(bridgedb_pub: VerifyingKey, rng: &mut (impl CryptoRng + RngCore)) -> Self {
        // Initialization
        cmz_group_init(G::hash_from_bytes::<Sha512>(b"CMZ Generator A"));
        // Create the private and public keys for each of the types of
        // credential with 'true' to indicate uCMZ
        let (lox_priv, lox_pub) = Lox::gen_keys(rng, true);
        let (migration_priv, migration_pub) = Migration::gen_keys(rng, true);
        let (migrationkey_priv, migrationkey_pub) = MigrationKey::gen_keys(rng, true);
        let (reachability_priv, reachability_pub) = BucketReachability::gen_keys(rng, true);
        let (invitation_priv, invitation_pub) = Invitation::gen_keys(rng, true);
        Self {
            lox_priv,
            lox_pub,
            migration_priv,
            migration_pub,
            migrationkey_priv,
            migrationkey_pub,
            reachability_priv,
            reachability_pub,
            invitation_priv,
            invitation_pub,
            bridgedb_pub,
            bridge_table: Default::default(),
            //            tp_bridge_infos: HashMap::<String, BridgeVerificationInfo>::new(),
            trustup_migration_table: MigrationTable::new(MigrationType::TrustUpgrade),
            blockage_migration_table: MigrationTable::new(MigrationType::Blockage),
            bridgedb_pub_filter: Default::default(),
            id_filter: Default::default(),
            inv_id_filter: Default::default(),
            trust_promotion_filter: Default::default(),
            time_offset: time::Duration::ZERO,
            old_keys: Default::default(),
            old_filters: Default::default(),
        }
    }

    pub fn rotate_lox_keys(&mut self, rng: &mut (impl CryptoRng + RngCore)) {
        let (updated_lox_priv, updated_lox_pub) = Lox::gen_keys(rng, true);
        // Store the old keys until the next key rotation (this should happen no more than 511 days after the
        // last rotation to ensure that all credentials issued with the old key can be updated
        self.old_keys.lox_keys.push(OldKeyStore {
            priv_key: self.lox_priv.clone(),
            pub_key: self.lox_pub.clone(),
        });
        // Move the old lox id filter to the old_lox_id_filter
        self.old_filters.lox_filter.push(self.id_filter.clone());
        // TODO: Commit to the new keys and post the commitment somewhere public that can be verified
        // by users, ideally
        self.lox_priv = updated_lox_priv;
        self.lox_pub = updated_lox_pub;
        self.id_filter = Default::default();
    }

    pub fn rotate_invitation_keys(&mut self, rng: &mut (impl CryptoRng + RngCore)) {
        let (updated_invitation_priv, updated_invitation_pub) = Invitation::gen_keys(rng, true);
        // Store the old keys until the next key rotation (this should happen no more than 511 days after the
        // last rotation to ensure that all credentials issued with the old key can be updated
        self.old_keys.invitation_keys.push(OldKeyStore {
            priv_key: self.invitation_priv.clone(),
            pub_key: self.invitation_pub.clone(),
        });
        // Move the old invitation id filter to the old_invitation_id_filter
        self.old_filters
            .invitation_filter
            .push(self.inv_id_filter.clone());
        // TODO: Commit to the new keys and post the commitment somewhere public that can be verified
        // by users, ideally
        self.invitation_priv = updated_invitation_priv;
        self.invitation_pub = updated_invitation_pub;
        self.inv_id_filter = Default::default();
    }

    pub fn rotate_bridgedb_keys(&mut self, new_bridgedb_pub: VerifyingKey) {
        // Store the old verifying key until the next key rotation (this should happen no more often than the
        // we would reasonably expect a user to redeem an open invitation token to ensure that all invitations
        // issued with the old key can be updated)
        self.old_keys.bridgedb_key.push(self.bridgedb_pub);
        // Move the old lox id filter to the old_lox_id_filter
        self.old_filters
            .openinv_filter
            .push(self.bridgedb_pub_filter.clone());
        // TODO: Commit to the new keys and post the commitment somewhere public that can be verified
        // by users, ideally
        self.bridgedb_pub = new_bridgedb_pub;
        self.bridgedb_pub_filter = Default::default();
    }

    /// Insert a set of open invitation bridges.
    ///
    /// Each of the bridges will be given its own open invitation
    /// bucket, and the BridgeDb will be informed. A single bucket
    /// containing all of the bridges will also be created, with a trust
    /// upgrade migration from each of the single-bridge buckets.
    pub fn add_openinv_bridges(
        &mut self,
        bridges: [BridgeLine; MAX_BRIDGES_PER_BUCKET],
        bdb: &mut BridgeDb,
    ) -> Result<(), NoAvailableIDError> {
        let bindex = self.find_next_available_key(bdb)?;
        self.bridge_table.new_bucket(bindex, &bridges);
        let mut single = [BridgeLine::default(); MAX_BRIDGES_PER_BUCKET];
        for b in bridges.iter() {
            let sindex = self.find_next_available_key(bdb)?;
            single[0] = *b;
            self.bridge_table.new_bucket(sindex, &single);
            self.bridge_table.open_inv_keys.push((sindex, self.today()));
            bdb.insert_openinv(sindex);
            self.trustup_migration_table.table.insert(sindex, bindex);
        }
        Ok(())
    }

    pub fn is_empty(&self) -> bool {
        self.bridge_table.buckets.is_empty()
    }

    pub fn reachable_length(&self) -> usize {
        self.bridge_table.reachable.len()
    }

    pub fn unallocated_length(&self) -> usize {
        self.bridge_table.unallocated_bridges.len()
    }

    pub fn spares_length(&self) -> usize {
        self.bridge_table.spares.len()
    }

    pub fn openinv_length(&self, bdb: &mut BridgeDb) -> usize {
        bdb.openinv_length()
    }

    /// Insert a hot spare bucket of bridges
    pub fn add_spare_bucket(
        &mut self,
        bucket: [BridgeLine; MAX_BRIDGES_PER_BUCKET],
        bdb: &mut BridgeDb,
    ) -> Result<(), NoAvailableIDError> {
        let index = self.find_next_available_key(bdb)?;
        self.bridge_table.new_bucket(index, &bucket);
        self.bridge_table.spares.insert(index);
        Ok(())
    }

    /// When syncing the Lox bridge table with rdsys, this function returns any bridges
    /// that are found in the Lox bridge table that are not found in the Vector
    /// of bridges received from rdsys through the Lox distributor.
    pub fn find_and_remove_unaccounted_for_bridges(
        &mut self,
        accounted_for_bridges: Vec<u64>,
    ) -> Vec<BridgeLine> {
        let mut unaccounted_for: Vec<BridgeLine> = Vec::new();
        for (k, _v) in self.bridge_table.reachable.clone() {
            if !accounted_for_bridges.contains(&k.uid_fingerprint) {
                unaccounted_for.push(k);
            }
        }
        unaccounted_for
    }

    /// Allocate single left over bridges to an open invitation bucket
    pub fn allocate_bridges(
        &mut self,
        distributor_bridges: &mut Vec<BridgeLine>,
        bdb: &mut BridgeDb,
    ) {
        while let Some(bridge) = distributor_bridges.pop() {
            self.bridge_table.unallocated_bridges.push(bridge);
        }
        while self.bridge_table.unallocated_bridges.len() >= MAX_BRIDGES_PER_BUCKET {
            let mut bucket = [BridgeLine::default(); MAX_BRIDGES_PER_BUCKET];
            for bridge in bucket.iter_mut() {
                *bridge = self.bridge_table.unallocated_bridges.pop().unwrap();
            }
            match self.add_openinv_bridges(bucket, bdb) {
                Ok(_) => continue,
                Err(e) => {
                    println!("Error: {:?}", e);
                    for bridge in bucket {
                        self.bridge_table.unallocated_bridges.push(bridge);
                    }
                }
            }
        }
    }

    // Update the details of a bridge in the bridge table. This assumes that the IP and Port
    // of a given bridge remains the same and thus can be updated.
    // First we must retrieve the list of reachable bridges, then we must search for any matching our partial key
    // which will include the IP and Port. Finally we can replace the original bridge with the updated bridge.
    // Returns true if the bridge has successfully updated
    pub fn bridge_update(&mut self, bridge: &BridgeLine) -> bool {
        let mut res: bool = false; //default False to assume that update failed
        let reachable_bridges = self.bridge_table.reachable.clone();
        for reachable_bridge in reachable_bridges {
            if reachable_bridge.0.uid_fingerprint == bridge.uid_fingerprint {
                // Now we must remove the old bridge from the table and insert the new bridge in its place
                // i.e., in the same bucket and with the same permissions.
                let positions = self.bridge_table.reachable.get(&reachable_bridge.0);
                if let Some(v) = positions {
                    for (bucketnum, offset) in v.iter() {
                        let mut bridgelines = match self.bridge_table.buckets.get(bucketnum) {
                            Some(bridgelines) => *bridgelines,
                            None => return res,
                        };
                        assert!(bridgelines[*offset] == reachable_bridge.0);
                        bridgelines[*offset] = *bridge;
                        self.bridge_table.buckets.insert(*bucketnum, bridgelines);
                        /*                   #[cfg(feature = "blockage-detection")]
                        let (fingerprint_str, bucket) =
                            self.get_tp_bucket_and_fingerprint(bridge, bucketnum);
                        // Add bucket to existing entry or add new entry
                        #[cfg(feature = "blockage-detection")]
                        match self.tp_bridge_infos.get_mut(&fingerprint_str) {
                            Some(info) => {
                                info.buckets.insert(bucket);
                            }
                            None => {
                                let mut buckets = HashSet::<Scalar>::new();
                                buckets.insert(bucket);
                                self.tp_bridge_infos.insert(
                                    fingerprint_str,
                                    BridgeVerificationInfo {
                                        bridge_line: *bridge,
                                        buckets,
                                    },
                                );
                            }
                        }; */
                        if !self.bridge_table.buckets.contains_key(bucketnum) {
                            return res;
                        }
                    }
                    res = true;
                } else {
                    return res;
                }
                // We must also remove the old bridge from the reachable bridges table
                // and add the new bridge
                self.bridge_table.reachable.remove(&reachable_bridge.0);
                self.bridge_table
                    .reachable
                    .insert(*bridge, reachable_bridge.1);
                return res;
            }
        }
        // Also check the unallocated bridges just in case there is a bridge that should be updated there
        let unallocated_bridges = self.bridge_table.unallocated_bridges.clone();
        for (i, unallocated_bridge) in unallocated_bridges.iter().enumerate() {
            if unallocated_bridge.uid_fingerprint == bridge.uid_fingerprint {
                // Now we must remove the old bridge from the unallocated bridges and insert the new bridge
                // in its place
                self.bridge_table.unallocated_bridges.remove(i);
                self.bridge_table.unallocated_bridges.push(*bridge);
                res = true;
            }
        }
        // If this is returned, we assume that the bridge wasn't found in the bridge table
        // and therefore should be treated as a "new bridge"
        res
    }

    // Repurpose a bucket of spares into unallocated bridges
    pub fn dissolve_spare_bucket(&mut self, key: u32) -> Result<(), BridgeTableError> {
        self.bridge_table.spares.remove(&key);
        // Get the actual bridges from the spare bucket
        let spare_bucket = self
            .bridge_table
            .buckets
            .remove(&key)
            .ok_or(BridgeTableError::MissingBucket(key))?;
        for bridge in spare_bucket.iter() {
            self.bridge_table.unallocated_bridges.push(*bridge);
            // Mark bucket as unreachable while it is unallocated
            self.bridge_table.reachable.remove(bridge);
        }
        self.bridge_table.keys.remove(&key);
        self.bridge_table.recycleable_keys.push(key);
        Ok(())
    }

    // Removes an unallocated bridge and returns it if it was present
    pub fn remove_unallocated(&mut self, bridge: &BridgeLine) -> Option<BridgeLine> {
        //    #[cfg(feature = "blockage-detection")]
        //    let fingerprint_str = self.fingerprint_hasher(bridge.unhashed_fingerprint);
        match self
            .bridge_table
            .unallocated_bridges
            .iter()
            .position(|x| x == bridge)
        {
            Some(index) => Some({
                //          #[cfg(feature = "blockage-detection")]
                //        self.tp_bridge_infos.remove_entry(&fingerprint_str);
                self.bridge_table.unallocated_bridges.swap_remove(index)
            }),
            None => None,
        }
    }

    /// Attempt to remove a bridge that is failing tests and replace it with a bridge from
    /// available_bridge or from a spare bucket
    pub fn bridge_replace(
        &mut self,
        bridge: &BridgeLine,
        available_bridge: Option<BridgeLine>,
    ) -> ReplaceSuccess {
        let reachable_bridges = &self.bridge_table.reachable.clone();
        let Some(positions) = reachable_bridges.get(bridge) else {
            match self.remove_unallocated(bridge) {
                Some(_) => {
                    return ReplaceSuccess::Removed;
                }
                None => {
                    return ReplaceSuccess::NotFound;
                }
            }
        };
        // Check if the bridge is in a spare bucket first, if it is, dissolve the bucket
        if let Some(spare) = self
            .bridge_table
            .spares
            .iter()
            .find(|x| positions.iter().any(|(bucketnum, _)| &bucketnum == x))
            .cloned()
        {
            let Ok(_) = self.dissolve_spare_bucket(spare) else {
                return ReplaceSuccess::NotReplaced;
            };
            // Next Check if the bridge is in the unallocated bridges and remove the bridge if so
            // Bridges in spare buckets should have been moved to the unallocated bridges
            match self.remove_unallocated(bridge) {
                Some(_) => {
                    return ReplaceSuccess::Removed;
                }
                None => {
                    return ReplaceSuccess::NotFound;
                }
            }
        }
        // select replacement:
        //   - first try the given bridge
        //   - second try to pick one from the set of available bridges
        //   - third dissolve a spare bucket to create more available bridges
        let Some(replacement) = available_bridge.or_else(|| {
            self.bridge_table.unallocated_bridges.pop().or_else(|| {
                let spare = self
                    .bridge_table
                    .spares
                    .iter()
                    // in case bridge is a spare, avoid replacing it with itself
                    .find(|x| !positions.iter().any(|(bucketnum, _)| &bucketnum == x))
                    .cloned()?;
                let Ok(_) = self.dissolve_spare_bucket(spare) else {
                    return None;
                };
                self.bridge_table.unallocated_bridges.pop()
            })
        }) else {
            // If there are no available bridges that can be assigned here, the only thing
            // that can be done is return an indication that updating the gone bridge
            // didn't work.
            // In this case, we do not mark the bridge as unreachable or remove it from the
            // reachable bridges so that we can still find it when a new bridge does become available
            println!("No available bridges");
            return ReplaceSuccess::NotReplaced;
        };
        for (bucketnum, offset) in positions.iter() {
            let mut bridgelines = match self.bridge_table.buckets.get(bucketnum) {
                Some(bridgelines) => *bridgelines,
                None => return ReplaceSuccess::NotFound,
            };
            assert!(bridgelines[*offset] == *bridge);
            bridgelines[*offset] = replacement;
            self.bridge_table.buckets.insert(*bucketnum, bridgelines);
            // Remove the bridge from the reachable bridges and add new bridge
            self.bridge_table
                .reachable
                .insert(replacement, positions.clone());
            // Remove the bridge from the bucket
            self.bridge_table.reachable.remove(bridge);
        }
        ReplaceSuccess::Replaced
    }

    /*    pub fn get_bridge_verification_info(
            &mut self,
            bridge_str: &String,
        ) -> Option<&BridgeVerificationInfo> {
            self.tp_bridge_infos.get(bridge_str)
        }

        // Remove Bridge Info for blocked bridge and return the bridgeline with the given fingerprint
        pub fn block_by_string(&mut self, bridge_str: &String) -> Option<BridgeLine> {
            if let Some(bridge_verification_info) = self.tp_bridge_infos.remove(bridge_str) {
                return Some(bridge_verification_info.bridge_line);
            }
            None
        }
    */

    /// Mark a bridge as blocked
    ///
    /// This bridge will be removed from each of the buckets that
    /// contains it. If any of those are open-invitation buckets, the
    /// trust upgrade migration for that bucket will be removed and the
    /// BridgeDb will be informed to stop handing out that bridge. If
    /// any of those are trusted buckets where the number of reachable
    /// bridges has fallen below the threshold, a blockage migration
    /// from that bucket to a spare bucket will be added, and the spare
    /// bucket will be removed from the list of hot spares. In
    /// addition, if the blocked bucket was the _target_ of a blockage
    /// migration, change the target to the new (formerly spare) bucket.
    /// Returns true if sucessful, or false if it needed a hot spare but
    /// there was none available.
    pub fn bridge_blocked(&mut self, bridge: &BridgeLine, bdb: &mut BridgeDb) -> bool {
        let mut res: bool = true;
        if self.remove_unallocated(bridge).is_some() {
            return true;
        }
        if let Some(positions) = self.bridge_table.reachable.get(bridge) {
            for (bucketnum, offset) in positions.iter() {
                // Count how many bridges in this bucket are reachable
                let mut bucket = match self.bridge_table.buckets.get(bucketnum) {
                    Some(bridgelines) => *bridgelines,
                    None => return false, // This should not happen
                };
                // Remove the bridge from the bucket
                assert!(bucket[*offset] == *bridge);
                bucket[*offset] = BridgeLine::default();

                // If this is an open invitation bucket, there is only one bridge, remove bucket
                if bdb.openinv_buckets.contains(bucketnum)
                    || bdb.distributed_buckets.contains(bucketnum)
                {
                    bdb.remove_blocked_or_expired_buckets(bucketnum);
                    self.trustup_migration_table.table.remove(bucketnum);
                    continue;
                }

                // If this bucket still has an acceptable number of bridges, continue
                let numreachable = bucket
                    .iter()
                    .filter(|br| self.bridge_table.reachable.contains_key(br))
                    .count();
                if numreachable != MIN_BUCKET_REACHABILITY {
                    // No
                    continue;
                }

                // Remove any trust upgrade migrations to this bucket
                self.trustup_migration_table
                    .table
                    .retain(|_, &mut v| v != *bucketnum);

                // If there are no spares, delete blockage migrations leading to this bucket
                if self.bridge_table.spares.is_empty() {
                    res = false;
                    self.blockage_migration_table
                        .table
                        .retain(|_, &mut v| v != *bucketnum);
                    continue;
                }
                // Get the first spare and remove it from the spares
                // set.
                let spare = *self.bridge_table.spares.iter().next().unwrap();
                self.bridge_table.spares.remove(&spare);
                self.bridge_table
                    .blocked_keys
                    .push((*bucketnum, self.today()));
                // Add a blockage migration from this bucket to the spare
                self.blockage_migration_table
                    .table
                    .insert(*bucketnum, spare);
                // Change any blockage migrations with this bucket
                // as the destination to the spare
                for (_, v) in self.blockage_migration_table.table.iter_mut() {
                    if *v == *bucketnum {
                        *v = spare;
                    }
                }
            }
        }
        self.bridge_table.reachable.remove(bridge);

        res
    }

    // Since buckets are moved around in the bridge_table, finding a lookup key that
    // does not overwrite existing bridges could become an issue.We keep a list
    // of recycleable lookup keys from buckets that have been removed and prioritize
    // this list before increasing the counter
    fn find_next_available_key(&mut self, bdb: &mut BridgeDb) -> Result<u32, NoAvailableIDError> {
        self.clean_up_expired_buckets(bdb);
        if self.bridge_table.recycleable_keys.is_empty() {
            let mut test_index = 1;
            let mut test_counter = self.bridge_table.counter.wrapping_add(test_index);
            let mut i = 0;
            while self.bridge_table.buckets.contains_key(&test_counter) && i < 5000 {
                test_index += 1;
                test_counter = self.bridge_table.counter.wrapping_add(test_index);
                i += 1;
                if i == 5000 {
                    return Err(NoAvailableIDError::ExhaustedIndexer);
                }
            }
            self.bridge_table.counter = self.bridge_table.counter.wrapping_add(test_index);
            Ok(self.bridge_table.counter)
        } else {
            Ok(self.bridge_table.recycleable_keys.pop().unwrap())
        }
    }

    // This function looks for and removes buckets so their indexes can be reused
    // This should include buckets that have been blocked for a sufficiently long period
    // that we no longer want to allow migration to, or else, open-entry buckets that
    // have been unblocked long enough to become trusted and who's users' credentials
    // would have expired (after EXPIRY_DATE)
    pub fn clean_up_expired_buckets(&mut self, bdb: &mut BridgeDb) {
        // First check if there are any blocked indexes that are old enough to be replaced
        self.clean_up_blocked();
        // Next do the same for open_invitations buckets
        self.clean_up_open_entry(bdb);
    }

    /// Cleans up exipred blocked buckets
    fn clean_up_blocked(&mut self) {
        // If there are expired blockages, separate them from the fresh blockages
        #[allow(clippy::type_complexity)]
        let (expired, fresh): (Vec<(u32, u32)>, Vec<(u32, u32)>) = self
            .bridge_table
            .blocked_keys
            .iter()
            .partition(|&x| x.1 + EXPIRY_DATE < self.today());
        for item in expired {
            let key = item.0;
            // check each single bridge line and ensure none are still marked as reachable.
            // if any are still reachable, remove from reachable bridges.
            // When syncing resources, we will likely have to reallocate this bridge but if it hasn't already been
            // blocked, this might be fine?
            let bridgelines = self.bridge_table.buckets.get(&key).unwrap();
            for bridgeline in bridgelines {
                // If the bridge hasn't been set to default, assume it's still reachable
                if bridgeline.port > 0 {
                    // Move to unallocated bridges
                    self.bridge_table.unallocated_bridges.push(*bridgeline);
                    // Make sure bridge is removed from reachable bridges
                    self.bridge_table.reachable.remove(bridgeline);
                }
            }
            // Then remove the bucket and keys at the specified index
            self.bridge_table.buckets.remove(&key);
            self.bridge_table.keys.remove(&key);
            //and add them to the recyclable keys
            self.bridge_table.recycleable_keys.push(key);
            // Remove the expired blocked bucket from the blockage migration table,
            // assuming that anyone that has still not attempted to migrate from their
            // blocked bridge after the EXPIRY_DATE probably doesn't still need to migrate.
            self.blockage_migration_table.table.retain(|&k, _| k != key);
        }
        // Finally, update the blocked_keys vector to only include the fresh keys
        self.bridge_table.blocked_keys = fresh
    }

    /// Cleans up expired open invitation buckets
    fn clean_up_open_entry(&mut self, bdb: &mut BridgeDb) {
        // Separate exipred from fresh open invitation indexes
        #[allow(clippy::type_complexity)]
        let (expired, fresh): (Vec<(u32, u32)>, Vec<(u32, u32)>) = self
            .bridge_table
            .open_inv_keys
            .iter()
            .partition(|&x| x.1 + EXPIRY_DATE < self.today());
        for item in expired {
            let key = item.0;
            // We should check that the items were actually distributed before they are removed
            if !bdb.distributed_buckets.contains(&key) {
                // TODO: Add prometheus metric for this?
                println!("This bucket was not actually distributed!");
            }
            bdb.remove_blocked_or_expired_buckets(&key);
            // Remove any trust upgrade migrations from this
            // bucket
            self.trustup_migration_table.table.retain(|&k, _| k != key);
            self.bridge_table.buckets.remove(&key);
            self.bridge_table.keys.remove(&key);
            //and add them to the recyclable keys
            self.bridge_table.recycleable_keys.push(key);
        }
        // update the open_inv_keys vector to only include the fresh keys
        self.bridge_table.open_inv_keys = fresh
    }

    /// Get today's (real or simulated) date as u32
    pub fn today(&self) -> u32 {
        // We will not encounter negative Julian dates (~6700 years ago)
        // or ones larger than 32 bits
        (time::OffsetDateTime::now_utc().date() + self.time_offset)
            .to_julian_day()
            .try_into()
            .unwrap()
    }

    /// Get today's (real or simulated) date as a DateTime<Utc> value
    pub fn today_date(&self) -> DateTime<Utc> {
        Utc::now()
    }

    /// Get a reference to the encrypted bridge table.
    ///
    /// Be sure to call this function when you want the latest version
    /// of the table, since it will put fresh Bucket Reachability
    /// credentials in the buckets each day.
    pub fn enc_bridge_table(&mut self) -> &HashMap<u32, EncryptedBucket> {
        let today = self.today();
        if self.bridge_table.date_last_enc != today {
            self.bridge_table
                .encrypt_table(today, &self.reachability_priv);
        }
        &self.bridge_table.encbuckets
    }

    // For testing only: manually advance the day by the given number
    // of days
    #[cfg(feature = "test")]
    pub fn advance_days(&mut self, days: u16) {
        self.time_offset += time::Duration::days(days.into());
    }
}

pub fn scalar_u32(s: &Scalar) -> Option<u32> {
    // Check that the top 28 bytes of the Scalar are 0
    let sbytes: &[u8; 32] = s.as_bytes();
    if sbytes[4..].ct_eq(&[0u8; 28]).unwrap_u8() == 0 {
        return None;
    }
    Some(u32::from_le_bytes(sbytes[..4].try_into().unwrap()))
}