Merge pull request #26 from garious/add-accountant

Add testnode and client-demo

.codecov.yml

@@ -0,0 +1,2 @@
+ignore:
+  - "src/bin" 

.travis.yml

@@ -9,7 +9,7 @@ matrix:
   - rust: stable
   - rust: nightly
     env:
-    - FEATURES='unstable'
+    - FEATURES='asm,unstable'
 before_script: |
   export PATH="$PATH:$HOME/.cargo/bin"
   rustup component add rustfmt-preview

Cargo.toml

@@ -1,19 +1,42 @@
 [package]
 name = "silk"
 description = "A silky smooth implementation of the Loom architecture"
-version = "0.1.1"
+version = "0.3.0"
+documentation = "https://docs.rs/silk"
+homepage = "http://loomprotocol.com/"
+repository = "https://github.com/loomprotocol/silk"
 authors = [
     "Anatoly Yakovenko <aeyakovenko@gmail.com>",
     "Greg Fitzgerald <garious@gmail.com>",
 ]
 license = "Apache-2.0"
 
+[[bin]]
+name = "silk-demo"
+path = "src/bin/demo.rs"
+
+[[bin]]
+name = "silk-client-demo"
+path = "src/bin/client-demo.rs"
+
+[[bin]]
+name = "silk-testnode"
+path = "src/bin/testnode.rs"
+
 [badges]
 codecov = { repository = "loomprotocol/silk", branch = "master", service = "github" }
 
 [features]
 unstable = []
+asm = ["sha2-asm"]
 
 [dependencies]
 rayon = "1.0.0"
-itertools = "0.7.6"
+sha2 = "0.7.0"
+sha2-asm = {version="0.3", optional=true}
+generic-array = { version = "0.9.0", default-features = false, features = ["serde"] }
+serde = "1.0.27"
+serde_derive = "1.0.27"
+ring = "0.12.1"
+untrusted = "0.5.1"
+bincode = "1.0.0"

README.md

@@ -3,18 +3,83 @@
 [![Build Status](https://travis-ci.org/loomprotocol/silk.svg?branch=master)](https://travis-ci.org/loomprotocol/silk)
 [![codecov](https://codecov.io/gh/loomprotocol/silk/branch/master/graph/badge.svg)](https://codecov.io/gh/loomprotocol/silk)
 
-# Silk, A Silky Smooth Implementation of the Loom Architecture
+# Silk, a silky smooth implementation of the Loom specification
 
 Loom is a new achitecture for a high performance blockchain. Its whitepaper boasts a theoretical
-throughput of 710k transactions per second on a 1 gbps network. The first implementation of the
-whitepaper is happening in the 'loomprotocol/loom' repository. That repo is aggressively moving
-forward, looking to de-risk technical claims as quickly as possible. This repo is quite a bit
-different philosophically. Here we assume the Loom architecture is sound and worthy of building
-a community around. We care a great deal about quality, clarity and short learning curve. We
-avoid the use of `unsafe` Rust and an write tests for *everything*.  Optimizations are only
-added when corresponding benchmarks are also added that demonstrate real performance boots. We
-expect the feature set here will always be a long ways behind the loom repo, but that this is
-an implementation you can take to the bank, literally.
+throughput of 710k transactions per second on a 1 gbps network. The specification is implemented
+in two git repositories. Reserach is performed in the loom repository. That work drives the
+Loom specification forward. This repository, on the other hand, aims to implement the specification
+as-is.  We care a great deal about quality, clarity and short learning curve. We avoid the use
+of `unsafe` Rust and write tests for *everything*.  Optimizations are only added when
+corresponding benchmarks are also added that demonstrate real performance boosts. We expect the
+feature set here will always be a ways behind the loom repo, but that this is an implementation
+you can take to the bank, literally.
+
+# Usage
+
+Add the latest [silk package](https://crates.io/crates/silk) to the `[dependencies]` section
+of your Cargo.toml.
+
+Create a *Historian* and send it *events* to generate an *event log*, where each log *entry*
+is tagged with the historian's latest *hash*. Then ensure the order of events was not tampered
+with by verifying each entry's hash can be generated from the hash in the previous entry:
+
+![historian](https://user-images.githubusercontent.com/55449/36633440-f76f7bb8-1952-11e8-8328-387861d3d464.png)
+
+```rust
+extern crate silk;
+
+use silk::historian::Historian;
+use silk::log::{verify_slice, Entry, Event, Sha256Hash};
+use std::thread::sleep;
+use std::time::Duration;
+use std::sync::mpsc::SendError;
+
+fn create_log(hist: &Historian) -> Result<(), SendError<Event>> {
+    sleep(Duration::from_millis(15));
+    let data = Sha256Hash::default();
+    hist.sender.send(Event::Discovery { data })?;
+    sleep(Duration::from_millis(10));
+    Ok(())
+}
+
+fn main() {
+    let seed = Sha256Hash::default();
+    let hist = Historian::new(&seed, Some(10));
+    create_log(&hist).expect("send error");
+    drop(hist.sender);
+    let entries: Vec<Entry> = hist.receiver.iter().collect();
+    for entry in &entries {
+        println!("{:?}", entry);
+    }
+
+    // Proof-of-History: Verify the historian learned about the events
+    // in the same order they appear in the vector.
+    assert!(verify_slice(&entries, &seed));
+}
+```
+
+Running the program should produce a log similar to:
+
+```rust
+Entry { num_hashes: 0, end_hash: [0, ...], event: Tick }
+Entry { num_hashes: 2, end_hash: [67, ...], event: Discovery { data: [37, ...] } }
+Entry { num_hashes: 3, end_hash: [123, ...], event: Tick }
+```
+
+Proof-of-History
+---
+
+Take note of the last line:
+
+```rust
+assert!(verify_slice(&entries, &seed));
+```
+
+[It's a proof!](https://en.wikipedia.org/wiki/Curry–Howard_correspondence) For each entry returned by the
+historian, we can verify that `end_hash` is the result of applying a sha256 hash to the previous `end_hash`
+exactly `num_hashes` times, and then hashing then event data on top of that. Because the event data is
+included in the hash, the events cannot be reordered without regenerating all the hashes.
 
 # Developing
 
@@ -57,5 +122,5 @@ $ rustup install nightly
 Run the benchmarks:
 
 ```bash
-$ cargo +nightly bench --features="unstable"
+$ cargo +nightly bench --features="asm,unstable"
 ```

diagrams/historian.msc

@@ -0,0 +1,18 @@
+msc {
+  client,historian,logger;
+
+  logger=>historian [ label = "e0 = Entry{hash: h0, n: 0, event: Tick}" ] ;
+  logger=>logger [ label = "h1 = hash(h0)" ] ;
+  logger=>logger [ label = "h2 = hash(h1)" ] ;
+  client=>historian [ label = "Discovery(d0)" ] ;
+  historian=>logger [ label = "Discovery(d0)" ] ;
+  logger=>logger [ label = "h3 = hash(h2 + d0)" ] ;
+  logger=>historian [ label = "e1 = Entry{hash: hash(h3), n: 2, event: Discovery(d0)}" ] ;
+  logger=>logger [ label = "h4 = hash(h3)" ] ;
+  logger=>logger [ label = "h5 = hash(h4)" ] ;
+  logger=>logger [ label = "h6 = hash(h5)" ] ;
+  logger=>historian [ label = "e2 = Entry{hash: h6, n: 3, event: Tick}" ] ;
+  client=>historian [ label = "collect()" ] ;
+  historian=>client [ label = "entries = [e0, e1, e2]" ] ;
+  client=>client [ label = "verify_slice(entries, h0)" ] ;
+}

src/accountant.rs

@@ -0,0 +1,229 @@
+//! The `accountant` is a client of the `historian`. It uses the historian's
+//! event log to record transactions. Its users can deposit funds and
+//! transfer funds to other users.
+
+use log::{Event, PublicKey, Sha256Hash, Signature};
+use historian::Historian;
+use ring::signature::Ed25519KeyPair;
+use std::sync::mpsc::{RecvError, SendError};
+use std::collections::HashMap;
+
+pub struct Accountant {
+    pub historian: Historian<u64>,
+    pub balances: HashMap<PublicKey, u64>,
+    pub end_hash: Sha256Hash,
+}
+
+impl Accountant {
+    pub fn new(start_hash: &Sha256Hash, ms_per_tick: Option<u64>) -> Self {
+        let hist = Historian::<u64>::new(start_hash, ms_per_tick);
+        Accountant {
+            historian: hist,
+            balances: HashMap::new(),
+            end_hash: *start_hash,
+        }
+    }
+
+    pub fn process_event(self: &mut Self, event: &Event<u64>) {
+        match *event {
+            Event::Claim { key, data, .. } => {
+                if self.balances.contains_key(&key) {
+                    if let Some(x) = self.balances.get_mut(&key) {
+                        *x += data;
+                    }
+                } else {
+                    self.balances.insert(key, data);
+                }
+            }
+            Event::Transaction { from, to, data, .. } => {
+                if let Some(x) = self.balances.get_mut(&from) {
+                    *x -= data;
+                }
+                if self.balances.contains_key(&to) {
+                    if let Some(x) = self.balances.get_mut(&to) {
+                        *x += data;
+                    }
+                } else {
+                    self.balances.insert(to, data);
+                }
+            }
+            _ => (),
+        }
+    }
+
+    pub fn sync(self: &mut Self) {
+        let mut entries = vec![];
+        while let Ok(entry) = self.historian.receiver.try_recv() {
+            entries.push(entry);
+        }
+        // TODO: Does this cause the historian's channel to get blocked?
+        //use log::verify_slice_u64;
+        //println!("accountant: verifying {} entries...", entries.len());
+        //assert!(verify_slice_u64(&entries, &self.end_hash));
+        //println!("accountant: Done verifying {} entries.", entries.len());
+        if let Some(last_entry) = entries.last() {
+            self.end_hash = last_entry.end_hash;
+        }
+        for e in &entries {
+            self.process_event(&e.event);
+        }
+    }
+
+    pub fn deposit_signed(
+        self: &Self,
+        key: PublicKey,
+        data: u64,
+        sig: Signature,
+    ) -> Result<(), SendError<Event<u64>>> {
+        let event = Event::Claim { key, data, sig };
+        self.historian.sender.send(event)
+    }
+
+    pub fn deposit(
+        self: &Self,
+        n: u64,
+        keypair: &Ed25519KeyPair,
+    ) -> Result<(), SendError<Event<u64>>> {
+        use log::{get_pubkey, sign_serialized};
+        let key = get_pubkey(keypair);
+        let sig = sign_serialized(&n, keypair);
+        self.deposit_signed(key, n, sig)
+    }
+
+    pub fn transfer_signed(
+        self: &mut Self,
+        from: PublicKey,
+        to: PublicKey,
+        data: u64,
+        sig: Signature,
+    ) -> Result<(), SendError<Event<u64>>> {
+        if self.get_balance(&from).unwrap() < data {
+            // TODO: Replace the SendError result with a custom one.
+            println!("Error: Insufficient funds");
+            return Ok(());
+        }
+        let event = Event::Transaction {
+            from,
+            to,
+            data,
+            sig,
+        };
+        self.historian.sender.send(event)
+    }
+
+    pub fn transfer(
+        self: &mut Self,
+        n: u64,
+        keypair: &Ed25519KeyPair,
+        to: PublicKey,
+    ) -> Result<(), SendError<Event<u64>>> {
+        use log::{get_pubkey, sign_transaction_data};
+
+        let from = get_pubkey(keypair);
+        let sig = sign_transaction_data(&n, keypair, &to);
+        self.transfer_signed(from, to, n, sig)
+    }
+
+    pub fn get_balance(self: &mut Self, pubkey: &PublicKey) -> Result<u64, RecvError> {
+        self.sync();
+        Ok(*self.balances.get(pubkey).unwrap_or(&0))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::thread::sleep;
+    use std::time::Duration;
+    use log::{generate_keypair, get_pubkey};
+    use historian::ExitReason;
+
+    #[test]
+    fn test_accountant() {
+        let zero = Sha256Hash::default();
+        let mut acc = Accountant::new(&zero, Some(2));
+        let alice_keypair = generate_keypair();
+        let bob_keypair = generate_keypair();
+        acc.deposit(10_000, &alice_keypair).unwrap();
+        acc.deposit(1_000, &bob_keypair).unwrap();
+
+        sleep(Duration::from_millis(30));
+        let bob_pubkey = get_pubkey(&bob_keypair);
+        acc.transfer(500, &alice_keypair, bob_pubkey).unwrap();
+
+        sleep(Duration::from_millis(30));
+        assert_eq!(acc.get_balance(&bob_pubkey).unwrap(), 1_500);
+
+        drop(acc.historian.sender);
+        assert_eq!(
+            acc.historian.thread_hdl.join().unwrap().1,
+            ExitReason::RecvDisconnected
+        );
+    }
+
+    #[test]
+    fn test_invalid_transfer() {
+        let zero = Sha256Hash::default();
+        let mut acc = Accountant::new(&zero, Some(2));
+        let alice_keypair = generate_keypair();
+        let bob_keypair = generate_keypair();
+        acc.deposit(10_000, &alice_keypair).unwrap();
+        acc.deposit(1_000, &bob_keypair).unwrap();
+
+        sleep(Duration::from_millis(30));
+        let bob_pubkey = get_pubkey(&bob_keypair);
+        acc.transfer(10_001, &alice_keypair, bob_pubkey).unwrap();
+
+        sleep(Duration::from_millis(30));
+        let alice_pubkey = get_pubkey(&alice_keypair);
+        assert_eq!(acc.get_balance(&alice_pubkey).unwrap(), 10_000);
+        assert_eq!(acc.get_balance(&bob_pubkey).unwrap(), 1_000);
+
+        drop(acc.historian.sender);
+        assert_eq!(
+            acc.historian.thread_hdl.join().unwrap().1,
+            ExitReason::RecvDisconnected
+        );
+    }
+
+    #[test]
+    fn test_multiple_claims() {
+        let zero = Sha256Hash::default();
+        let mut acc = Accountant::new(&zero, Some(2));
+        let keypair = generate_keypair();
+        acc.deposit(1, &keypair).unwrap();
+        acc.deposit(2, &keypair).unwrap();
+
+        let pubkey = get_pubkey(&keypair);
+        sleep(Duration::from_millis(30));
+        assert_eq!(acc.get_balance(&pubkey).unwrap(), 3);
+
+        drop(acc.historian.sender);
+        assert_eq!(
+            acc.historian.thread_hdl.join().unwrap().1,
+            ExitReason::RecvDisconnected
+        );
+    }
+
+    #[test]
+    fn test_transfer_to_newb() {
+        let zero = Sha256Hash::default();
+        let mut acc = Accountant::new(&zero, Some(2));
+        let alice_keypair = generate_keypair();
+        let bob_keypair = generate_keypair();
+        acc.deposit(10_000, &alice_keypair).unwrap();
+
+        sleep(Duration::from_millis(30));
+        let bob_pubkey = get_pubkey(&bob_keypair);
+        acc.transfer(500, &alice_keypair, bob_pubkey).unwrap();
+
+        sleep(Duration::from_millis(30));
+        assert_eq!(acc.get_balance(&bob_pubkey).unwrap(), 500);
+
+        drop(acc.historian.sender);
+        assert_eq!(
+            acc.historian.thread_hdl.join().unwrap().1,
+            ExitReason::RecvDisconnected
+        );
+    }
+}

src/accountant_skel.rs

@@ -0,0 +1,75 @@
+use std::io;
+use accountant::Accountant;
+use log::{PublicKey, Signature};
+//use serde::Serialize;
+
+pub struct AccountantSkel {
+    pub obj: Accountant,
+}
+
+#[derive(Serialize, Deserialize, Debug)]
+pub enum Request {
+    Deposit {
+        key: PublicKey,
+        val: u64,
+        sig: Signature,
+    },
+    Transfer {
+        from: PublicKey,
+        to: PublicKey,
+        val: u64,
+        sig: Signature,
+    },
+    GetBalance {
+        key: PublicKey,
+    },
+}
+
+#[derive(Serialize, Deserialize, Debug)]
+pub enum Response {
+    Balance { key: PublicKey, val: u64 },
+}
+
+impl AccountantSkel {
+    pub fn new(obj: Accountant) -> Self {
+        AccountantSkel { obj }
+    }
+
+    pub fn process_request(self: &mut Self, msg: Request) -> Option<Response> {
+        match msg {
+            Request::Deposit { key, val, sig } => {
+                let _ = self.obj.deposit_signed(key, val, sig);
+                None
+            }
+            Request::Transfer { from, to, val, sig } => {
+                let _ = self.obj.transfer_signed(from, to, val, sig);
+                None
+            }
+            Request::GetBalance { key } => {
+                let val = self.obj.get_balance(&key).unwrap();
+                Some(Response::Balance { key, val })
+            }
+        }
+    }
+
+    /// TCP Server that forwards messages to Accountant methods.
+    pub fn serve(self: &mut Self, addr: &str) -> io::Result<()> {
+        use std::net::TcpListener;
+        use std::io::{Read, Write};
+        use bincode::{deserialize, serialize};
+        let listener = TcpListener::bind(addr)?;
+        let mut buf = vec![0u8; 1024];
+        loop {
+            //println!("skel: Waiting for incoming connections...");
+            let (mut stream, _from_addr) = listener.accept()?;
+            let _sz = stream.read(&mut buf)?;
+
+            // TODO: Return a descriptive error message if deserialization fails.
+            let req = deserialize(&buf).expect("deserialize request");
+
+            if let Some(resp) = self.process_request(req) {
+                stream.write(&serialize(&resp).expect("serialize response"))?;
+            }
+        }
+    }
+}

src/accountant_stub.rs

@@ -0,0 +1,116 @@
+//! The `accountant` is a client of the `historian`. It uses the historian's
+//! event log to record transactions. Its users can deposit funds and
+//! transfer funds to other users.
+
+use std::net::TcpStream;
+use std::io;
+use std::io::{Read, Write};
+use bincode::{deserialize, serialize};
+use log::{PublicKey, Signature};
+use ring::signature::Ed25519KeyPair;
+use accountant_skel::{Request, Response};
+
+pub struct AccountantStub {
+    pub addr: String,
+}
+
+impl AccountantStub {
+    pub fn new(addr: &str) -> Self {
+        AccountantStub {
+            addr: addr.to_string(),
+        }
+    }
+
+    pub fn deposit_signed(
+        self: &mut Self,
+        key: PublicKey,
+        val: u64,
+        sig: Signature,
+    ) -> io::Result<usize> {
+        let req = Request::Deposit { key, val, sig };
+        let data = serialize(&req).unwrap();
+        let mut stream = TcpStream::connect(&self.addr)?;
+        stream.write(&data)
+    }
+
+    pub fn deposit(self: &mut Self, n: u64, keypair: &Ed25519KeyPair) -> io::Result<usize> {
+        use log::{get_pubkey, sign_serialized};
+        let key = get_pubkey(keypair);
+        let sig = sign_serialized(&n, keypair);
+        self.deposit_signed(key, n, sig)
+    }
+
+    pub fn transfer_signed(
+        self: &mut Self,
+        from: PublicKey,
+        to: PublicKey,
+        val: u64,
+        sig: Signature,
+    ) -> io::Result<usize> {
+        let req = Request::Transfer { from, to, val, sig };
+        let data = serialize(&req).unwrap();
+        let mut stream = TcpStream::connect(&self.addr)?;
+        stream.write(&data)
+    }
+
+    pub fn transfer(
+        self: &mut Self,
+        n: u64,
+        keypair: &Ed25519KeyPair,
+        to: PublicKey,
+    ) -> io::Result<usize> {
+        use log::{get_pubkey, sign_transaction_data};
+        let from = get_pubkey(keypair);
+        let sig = sign_transaction_data(&n, keypair, &to);
+        self.transfer_signed(from, to, n, sig)
+    }
+
+    pub fn get_balance(self: &mut Self, pubkey: &PublicKey) -> io::Result<u64> {
+        let mut stream = TcpStream::connect(&self.addr)?;
+        let req = Request::GetBalance { key: *pubkey };
+        let data = serialize(&req).expect("serialize GetBalance");
+        stream.write(&data)?;
+        let mut buf = vec![0u8; 1024];
+        stream.read(&mut buf)?;
+        let resp = deserialize(&buf).expect("deserialize balance");
+        let Response::Balance { key, val } = resp;
+        assert_eq!(key, *pubkey);
+        Ok(val)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use accountant::Accountant;
+    use accountant_skel::AccountantSkel;
+    use std::thread::{sleep, spawn};
+    use std::time::Duration;
+    use log::{generate_keypair, get_pubkey, Sha256Hash};
+
+    #[test]
+    fn test_accountant_stub() {
+        let addr = "127.0.0.1:8000";
+        spawn(move || {
+            let zero = Sha256Hash::default();
+            let acc = Accountant::new(&zero, None);
+            let mut skel = AccountantSkel::new(acc);
+            skel.serve(addr).unwrap();
+        });
+
+        sleep(Duration::from_millis(30));
+
+        let mut acc = AccountantStub::new(addr);
+        let alice_keypair = generate_keypair();
+        let bob_keypair = generate_keypair();
+        acc.deposit(10_000, &alice_keypair).unwrap();
+        acc.deposit(1_000, &bob_keypair).unwrap();
+
+        sleep(Duration::from_millis(30));
+        let bob_pubkey = get_pubkey(&bob_keypair);
+        acc.transfer(500, &alice_keypair, bob_pubkey).unwrap();
+
+        sleep(Duration::from_millis(300));
+        assert_eq!(acc.get_balance(&bob_pubkey).unwrap(), 1_500);
+    }
+}

src/bin/client-demo.rs

@@ -0,0 +1,45 @@
+extern crate silk;
+
+fn main() {
+    use silk::accountant_stub::AccountantStub;
+    use std::thread::sleep;
+    use std::time::Duration;
+    use silk::log::{generate_keypair, get_pubkey};
+
+    let addr = "127.0.0.1:8000";
+    let mut acc = AccountantStub::new(addr);
+    let alice_keypair = generate_keypair();
+    let bob_keypair = generate_keypair();
+    let txs = 10_000;
+    println!("Depositing {} units in Alice's account...", txs);
+    acc.deposit(txs, &alice_keypair).unwrap();
+    //acc.deposit(1_000, &bob_keypair).unwrap();
+    println!("Done.");
+
+    sleep(Duration::from_millis(30));
+    let alice_pubkey = get_pubkey(&alice_keypair);
+    let bob_pubkey = get_pubkey(&bob_keypair);
+    println!("Transferring 1 unit {} times...", txs);
+    for _ in 0..txs {
+        acc.transfer(1, &alice_keypair, bob_pubkey).unwrap();
+    }
+    println!("Done.");
+
+    sleep(Duration::from_millis(20));
+    let mut alice_val = acc.get_balance(&alice_pubkey).unwrap();
+    while alice_val > 0 {
+        println!("Checking on Alice's Balance {}", alice_val);
+        sleep(Duration::from_millis(20));
+        alice_val = acc.get_balance(&alice_pubkey).unwrap();
+    }
+    println!("Done. Checking balances.");
+    println!(
+        "Alice's Final Balance {}",
+        acc.get_balance(&alice_pubkey).unwrap()
+    );
+
+    println!(
+        "Bob's Final Balance {}",
+        acc.get_balance(&bob_pubkey).unwrap()
+    );
+}

src/bin/demo.rs

@@ -0,0 +1,27 @@
+extern crate silk;
+
+use silk::historian::Historian;
+use silk::log::{verify_slice, Entry, Event, Sha256Hash};
+use std::thread::sleep;
+use std::time::Duration;
+use std::sync::mpsc::SendError;
+
+fn create_log(hist: &Historian<Sha256Hash>) -> Result<(), SendError<Event<Sha256Hash>>> {
+    sleep(Duration::from_millis(15));
+    let data = Sha256Hash::default();
+    hist.sender.send(Event::Discovery { data })?;
+    sleep(Duration::from_millis(10));
+    Ok(())
+}
+
+fn main() {
+    let seed = Sha256Hash::default();
+    let hist = Historian::new(&seed, Some(10));
+    create_log(&hist).expect("send error");
+    drop(hist.sender);
+    let entries: Vec<Entry<Sha256Hash>> = hist.receiver.iter().collect();
+    for entry in &entries {
+        println!("{:?}", entry);
+    }
+    assert!(verify_slice(&entries, &seed));
+}

src/bin/testnode.rs

@@ -0,0 +1,14 @@
+extern crate silk;
+
+use silk::accountant_skel::AccountantSkel;
+use silk::accountant::Accountant;
+use silk::log::Sha256Hash;
+
+fn main() {
+    let addr = "127.0.0.1:8000";
+    let zero = Sha256Hash::default();
+    let acc = Accountant::new(&zero, Some(1000));
+    let mut skel = AccountantSkel::new(acc);
+    println!("Listening on {}", addr);
+    skel.serve(addr).unwrap();
+}

src/event.rs

@@ -1,151 +0,0 @@
-//! The `event` crate provides the foundational data structures for Proof-of-History
-
-/// A Proof-of-History is an ordered log of events in time. Each entry contains three
-/// pieces of data. The 'num_hashes' field is the number of hashes performed since the previous
-/// entry.  The 'end_hash' field is the result of hashing 'end_hash' from the previous entry
-/// 'num_hashes' times.  The 'data' field is an optional foreign key (a hash) pointing to some
-/// arbitrary data that a client is looking to associate with the entry.
-///
-/// If you divide 'num_hashes' by the amount of time it takes to generate a new hash, you
-/// get a duration estimate since the last event. Since processing power increases
-/// over time, one should expect the duration 'num_hashes' represents to decrease proportionally.
-/// Though processing power varies across nodes, the network gives priority to the
-/// fastest processor. Duration should therefore be estimated by assuming that the hash
-/// was generated by the fastest processor at the time the entry was logged.
-pub struct Event {
-    pub num_hashes: u64,
-    pub end_hash: u64,
-    pub data: EventData,
-}
-
-/// When 'data' is Tick, the event represents a simple clock tick, and exists for the
-/// sole purpose of improving the performance of event log verification. A tick can
-/// be generated in 'num_hashes' hashes and verified in 'num_hashes' hashes.  By logging
-/// a hash alongside the tick, each tick and be verified in parallel using the 'end_hash'
-/// of the preceding tick to seed its hashing.
-pub enum EventData {
-    Tick,
-    UserDataKey(u64),
-}
-
-impl Event {
-    /// Creates an Event from the number of hashes 'num_hashes' since the previous event
-    /// and that resulting 'end_hash'.
-    pub fn new_tick(num_hashes: u64, end_hash: u64) -> Self {
-        let data = EventData::Tick;
-        Event {
-            num_hashes,
-            end_hash,
-            data,
-        }
-    }
-
-    /// Verifies self.end_hash is the result of hashing a 'start_hash' 'self.num_hashes' times.
-    pub fn verify(self: &Self, start_hash: u64) -> bool {
-        self.end_hash == next_tick(start_hash, self.num_hashes).end_hash
-    }
-}
-
-/// Creates the next Tick Event 'num_hashes' after 'start_hash'.
-pub fn next_tick(start_hash: u64, num_hashes: u64) -> Event {
-    use std::collections::hash_map::DefaultHasher;
-    use std::hash::{Hash, Hasher};
-    let mut end_hash = start_hash;
-    let mut hasher = DefaultHasher::new();
-    for _ in 0..num_hashes {
-        end_hash.hash(&mut hasher);
-        end_hash = hasher.finish();
-    }
-    Event::new_tick(num_hashes, end_hash)
-}
-
-/// Verifies the hashes and counts of a slice of events are all consistent.
-pub fn verify_slice(events: &[Event], start_hash: u64) -> bool {
-    use rayon::prelude::*;
-    let genesis = [Event::new_tick(0, start_hash)];
-    let event_pairs = genesis.par_iter().chain(events).zip(events);
-    event_pairs.all(|(x0, x1)| x1.verify(x0.end_hash))
-}
-
-/// Verifies the hashes and events serially. Exists only for reference.
-pub fn verify_slice_seq(events: &[Event], start_hash: u64) -> bool {
-    let genesis = [Event::new_tick(0, start_hash)];
-    let mut event_pairs = genesis.iter().chain(events).zip(events);
-    event_pairs.all(|(x0, x1)| x1.verify(x0.end_hash))
-}
-
-/// Create a vector of Ticks of length 'len' from 'start_hash' hash and 'num_hashes'.
-pub fn create_ticks(start_hash: u64, num_hashes: u64, len: usize) -> Vec<Event> {
-    use itertools::unfold;
-    let mut events = unfold(start_hash, |state| {
-        let event = next_tick(*state, num_hashes);
-        *state = event.end_hash;
-        return Some(event);
-    });
-    events.by_ref().take(len).collect()
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_event_verify() {
-        assert!(Event::new_tick(0, 0).verify(0)); // base case
-        assert!(!Event::new_tick(0, 0).verify(1)); // base case, bad
-        assert!(next_tick(0, 1).verify(0)); // inductive step
-        assert!(!next_tick(0, 1).verify(1)); // inductive step, bad
-    }
-
-    #[test]
-    fn test_next_tick() {
-        assert_eq!(next_tick(0, 1).num_hashes, 1)
-    }
-
-    fn verify_slice_generic(verify_slice: fn(&[Event], u64) -> bool) {
-        assert!(verify_slice(&vec![], 0)); // base case
-        assert!(verify_slice(&vec![Event::new_tick(0, 0)], 0)); // singleton case 1
-        assert!(!verify_slice(&vec![Event::new_tick(0, 0)], 1)); // singleton case 2, bad
-        assert!(verify_slice(&create_ticks(0, 0, 2), 0)); // inductive step
-
-        let mut bad_ticks = create_ticks(0, 0, 2);
-        bad_ticks[1].end_hash = 1;
-        assert!(!verify_slice(&bad_ticks, 0)); // inductive step, bad
-    }
-
-    #[test]
-    fn test_verify_slice() {
-        verify_slice_generic(verify_slice);
-    }
-
-    #[test]
-    fn test_verify_slice_seq() {
-        verify_slice_generic(verify_slice_seq);
-    }
-
-}
-
-#[cfg(all(feature = "unstable", test))]
-mod bench {
-    extern crate test;
-    use self::test::Bencher;
-    use event;
-
-    #[bench]
-    fn event_bench(bencher: &mut Bencher) {
-        let start_hash = 0;
-        let events = event::create_ticks(start_hash, 100_000, 8);
-        bencher.iter(|| {
-            assert!(event::verify_slice(&events, start_hash));
-        });
-    }
-
-    #[bench]
-    fn event_bench_seq(bencher: &mut Bencher) {
-        let start_hash = 0;
-        let events = event::create_ticks(start_hash, 100_000, 8);
-        bencher.iter(|| {
-            assert!(event::verify_slice_seq(&events, start_hash));
-        });
-    }
-}

src/historian.rs

@@ -0,0 +1,210 @@
+//! The `historian` crate provides a microservice for generating a Proof-of-History.
+//! It logs Event items on behalf of its users. It continuously generates
+//! new hashes, only stopping to check if it has been sent an Event item. It
+//! tags each Event with an Entry and sends it back. The Entry includes the
+//! Event, the latest hash, and the number of hashes since the last event.
+//! The resulting stream of entries represents ordered events in time.
+
+use std::thread::JoinHandle;
+use std::sync::mpsc::{Receiver, SyncSender};
+use std::time::{Duration, SystemTime};
+use log::{hash, hash_event, verify_event, Entry, Event, Sha256Hash};
+use serde::Serialize;
+use std::fmt::Debug;
+
+pub struct Historian<T> {
+    pub sender: SyncSender<Event<T>>,
+    pub receiver: Receiver<Entry<T>>,
+    pub thread_hdl: JoinHandle<(Entry<T>, ExitReason)>,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum ExitReason {
+    RecvDisconnected,
+    SendDisconnected,
+}
+fn log_event<T: Serialize + Clone + Debug>(
+    sender: &SyncSender<Entry<T>>,
+    num_hashes: &mut u64,
+    end_hash: &mut Sha256Hash,
+    event: Event<T>,
+) -> Result<(), (Entry<T>, ExitReason)> {
+    *end_hash = hash_event(end_hash, &event);
+    let entry = Entry {
+        end_hash: *end_hash,
+        num_hashes: *num_hashes,
+        event,
+    };
+    if let Err(_) = sender.send(entry.clone()) {
+        return Err((entry, ExitReason::SendDisconnected));
+    }
+    *num_hashes = 0;
+    Ok(())
+}
+
+fn log_events<T: Serialize + Clone + Debug>(
+    receiver: &Receiver<Event<T>>,
+    sender: &SyncSender<Entry<T>>,
+    num_hashes: &mut u64,
+    end_hash: &mut Sha256Hash,
+    epoch: SystemTime,
+    num_ticks: &mut u64,
+    ms_per_tick: Option<u64>,
+) -> Result<(), (Entry<T>, ExitReason)> {
+    use std::sync::mpsc::TryRecvError;
+    loop {
+        if let Some(ms) = ms_per_tick {
+            let now = SystemTime::now();
+            if now > epoch + Duration::from_millis((*num_ticks + 1) * ms) {
+                log_event(sender, num_hashes, end_hash, Event::Tick)?;
+                *num_ticks += 1;
+            }
+        }
+        match receiver.try_recv() {
+            Ok(event) => {
+                if verify_event(&event) {
+                    log_event(sender, num_hashes, end_hash, event)?;
+                }
+            }
+            Err(TryRecvError::Empty) => {
+                return Ok(());
+            }
+            Err(TryRecvError::Disconnected) => {
+                let entry = Entry {
+                    end_hash: *end_hash,
+                    num_hashes: *num_hashes,
+                    event: Event::Tick,
+                };
+                return Err((entry, ExitReason::RecvDisconnected));
+            }
+        }
+    }
+}
+
+/// A background thread that will continue tagging received Event messages and
+/// sending back Entry messages until either the receiver or sender channel is closed.
+pub fn create_logger<T: 'static + Serialize + Clone + Debug + Send>(
+    start_hash: Sha256Hash,
+    ms_per_tick: Option<u64>,
+    receiver: Receiver<Event<T>>,
+    sender: SyncSender<Entry<T>>,
+) -> JoinHandle<(Entry<T>, ExitReason)> {
+    use std::thread;
+    thread::spawn(move || {
+        let mut end_hash = start_hash;
+        let mut num_hashes = 0;
+        let mut num_ticks = 0;
+        let epoch = SystemTime::now();
+        loop {
+            if let Err(err) = log_events(
+                &receiver,
+                &sender,
+                &mut num_hashes,
+                &mut end_hash,
+                epoch,
+                &mut num_ticks,
+                ms_per_tick,
+            ) {
+                return err;
+            }
+            end_hash = hash(&end_hash);
+            num_hashes += 1;
+        }
+    })
+}
+
+impl<T: 'static + Serialize + Clone + Debug + Send> Historian<T> {
+    pub fn new(start_hash: &Sha256Hash, ms_per_tick: Option<u64>) -> Self {
+        use std::sync::mpsc::sync_channel;
+        let (sender, event_receiver) = sync_channel(4000);
+        let (entry_sender, receiver) = sync_channel(4000);
+        let thread_hdl = create_logger(*start_hash, ms_per_tick, event_receiver, entry_sender);
+        Historian {
+            sender,
+            receiver,
+            thread_hdl,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use log::*;
+    use std::thread::sleep;
+    use std::time::Duration;
+
+    #[test]
+    fn test_historian() {
+        let zero = Sha256Hash::default();
+        let hist = Historian::new(&zero, None);
+
+        hist.sender.send(Event::Tick).unwrap();
+        sleep(Duration::new(0, 1_000_000));
+        hist.sender.send(Event::Discovery { data: zero }).unwrap();
+        sleep(Duration::new(0, 1_000_000));
+        hist.sender.send(Event::Tick).unwrap();
+
+        let entry0 = hist.receiver.recv().unwrap();
+        let entry1 = hist.receiver.recv().unwrap();
+        let entry2 = hist.receiver.recv().unwrap();
+
+        drop(hist.sender);
+        assert_eq!(
+            hist.thread_hdl.join().unwrap().1,
+            ExitReason::RecvDisconnected
+        );
+
+        assert!(verify_slice(&[entry0, entry1, entry2], &zero));
+    }
+
+    #[test]
+    fn test_historian_closed_sender() {
+        let zero = Sha256Hash::default();
+        let hist = Historian::<u8>::new(&zero, None);
+        drop(hist.receiver);
+        hist.sender.send(Event::Tick).unwrap();
+        assert_eq!(
+            hist.thread_hdl.join().unwrap().1,
+            ExitReason::SendDisconnected
+        );
+    }
+
+    #[test]
+    fn test_ticking_historian() {
+        let zero = Sha256Hash::default();
+        let hist = Historian::new(&zero, Some(20));
+        sleep(Duration::from_millis(30));
+        hist.sender.send(Event::Discovery { data: zero }).unwrap();
+        sleep(Duration::from_millis(15));
+        drop(hist.sender);
+        assert_eq!(
+            hist.thread_hdl.join().unwrap().1,
+            ExitReason::RecvDisconnected
+        );
+
+        let entries: Vec<Entry<Sha256Hash>> = hist.receiver.iter().collect();
+        assert!(entries.len() > 1);
+        assert!(verify_slice(&entries, &zero));
+    }
+
+    #[test]
+    fn test_bad_event_attack() {
+        let zero = Sha256Hash::default();
+        let hist = Historian::new(&zero, None);
+        let keypair = generate_keypair();
+        let event0 = Event::Claim {
+            key: get_pubkey(&keypair),
+            data: hash(b"goodbye cruel world"),
+            sig: sign_serialized(&hash(b"hello, world"), &keypair),
+        };
+        hist.sender.send(event0).unwrap();
+        drop(hist.sender);
+        assert_eq!(
+            hist.thread_hdl.join().unwrap().1,
+            ExitReason::RecvDisconnected
+        );
+        let entries: Vec<Entry<Sha256Hash>> = hist.receiver.iter().collect();
+        assert_eq!(entries.len(), 0);
+    }
+}

src/lib.rs

@@ -1,4 +1,15 @@
 #![cfg_attr(feature = "unstable", feature(test))]
-pub mod event;
-extern crate itertools;
+pub mod log;
+pub mod historian;
+pub mod accountant;
+pub mod accountant_skel;
+pub mod accountant_stub;
+extern crate bincode;
+extern crate generic_array;
 extern crate rayon;
+extern crate ring;
+extern crate serde;
+#[macro_use]
+extern crate serde_derive;
+extern crate sha2;
+extern crate untrusted;

src/log.rs

@@ -0,0 +1,440 @@
+//! The `log` crate provides the foundational data structures for Proof-of-History,
+//! an ordered log of events in time.
+
+/// Each log entry contains three pieces of data. The 'num_hashes' field is the number
+/// of hashes performed since the previous entry.  The 'end_hash' field is the result
+/// of hashing 'end_hash' from the previous entry 'num_hashes' times.  The 'event'
+/// field points to an Event that took place shortly after 'end_hash' was generated.
+///
+/// If you divide 'num_hashes' by the amount of time it takes to generate a new hash, you
+/// get a duration estimate since the last event. Since processing power increases
+/// over time, one should expect the duration 'num_hashes' represents to decrease proportionally.
+/// Though processing power varies across nodes, the network gives priority to the
+/// fastest processor. Duration should therefore be estimated by assuming that the hash
+/// was generated by the fastest processor at the time the entry was logged.
+
+use generic_array::GenericArray;
+use generic_array::typenum::{U32, U64};
+use ring::signature::Ed25519KeyPair;
+use serde::Serialize;
+
+pub type Sha256Hash = GenericArray<u8, U32>;
+pub type PublicKey = GenericArray<u8, U32>;
+pub type Signature = GenericArray<u8, U64>;
+
+#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
+pub struct Entry<T> {
+    pub num_hashes: u64,
+    pub end_hash: Sha256Hash,
+    pub event: Event<T>,
+}
+
+/// When 'event' is Tick, the event represents a simple clock tick, and exists for the
+/// sole purpose of improving the performance of event log verification. A tick can
+/// be generated in 'num_hashes' hashes and verified in 'num_hashes' hashes.  By logging
+/// a hash alongside the tick, each tick and be verified in parallel using the 'end_hash'
+/// of the preceding tick to seed its hashing.
+#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
+pub enum Event<T> {
+    Tick,
+    Discovery {
+        data: T,
+    },
+    Claim {
+        key: PublicKey,
+        data: T,
+        sig: Signature,
+    },
+    Transaction {
+        from: PublicKey,
+        to: PublicKey,
+        data: T,
+        sig: Signature,
+    },
+}
+
+impl<T> Entry<T> {
+    /// Creates a Entry from the number of hashes 'num_hashes' since the previous event
+    /// and that resulting 'end_hash'.
+    pub fn new_tick(num_hashes: u64, end_hash: &Sha256Hash) -> Self {
+        Entry {
+            num_hashes,
+            end_hash: *end_hash,
+            event: Event::Tick,
+        }
+    }
+}
+
+/// Return a new ED25519 keypair
+pub fn generate_keypair() -> Ed25519KeyPair {
+    use ring::{rand, signature};
+    use untrusted;
+    let rng = rand::SystemRandom::new();
+    let pkcs8_bytes = signature::Ed25519KeyPair::generate_pkcs8(&rng).unwrap();
+    signature::Ed25519KeyPair::from_pkcs8(untrusted::Input::from(&pkcs8_bytes)).unwrap()
+}
+
+/// Return the public key for the given keypair
+pub fn get_pubkey(keypair: &Ed25519KeyPair) -> PublicKey {
+    GenericArray::clone_from_slice(keypair.public_key_bytes())
+}
+
+/// Return a signature for the given data using the private key from the given keypair.
+pub fn sign_serialized<T: Serialize>(data: &T, keypair: &Ed25519KeyPair) -> Signature {
+    use bincode::serialize;
+    let serialized = serialize(data).unwrap();
+    GenericArray::clone_from_slice(keypair.sign(&serialized).as_ref())
+}
+
+/// Return a signature for the given transaction data using the private key from the given keypair.
+pub fn sign_transaction_data<T: Serialize>(
+    data: &T,
+    keypair: &Ed25519KeyPair,
+    to: &PublicKey,
+) -> Signature {
+    sign_serialized(&(data, to), keypair)
+}
+
+/// Return a Sha256 hash for the given data.
+pub fn hash(val: &[u8]) -> Sha256Hash {
+    use sha2::{Digest, Sha256};
+    let mut hasher = Sha256::default();
+    hasher.input(val);
+    hasher.result()
+}
+
+/// Return the hash of the given hash extended with the given value.
+pub fn extend_and_hash(end_hash: &Sha256Hash, ty: u8, val: &[u8]) -> Sha256Hash {
+    let mut hash_data = end_hash.to_vec();
+    hash_data.push(ty);
+    hash_data.extend_from_slice(val);
+    hash(&hash_data)
+}
+
+pub fn hash_event<T: Serialize>(end_hash: &Sha256Hash, event: &Event<T>) -> Sha256Hash {
+    use bincode::serialize;
+    match *event {
+        Event::Tick => *end_hash,
+        Event::Discovery { ref data } => extend_and_hash(end_hash, 1, &serialize(&data).unwrap()),
+        Event::Claim { key, ref data, sig } => {
+            let mut event_data = serialize(&data).unwrap();
+            event_data.extend_from_slice(&sig);
+            event_data.extend_from_slice(&key);
+            extend_and_hash(end_hash, 2, &event_data)
+        }
+        Event::Transaction {
+            from,
+            to,
+            ref data,
+            sig,
+        } => {
+            let mut event_data = serialize(&data).unwrap();
+            event_data.extend_from_slice(&sig);
+            event_data.extend_from_slice(&from);
+            event_data.extend_from_slice(&to);
+            extend_and_hash(end_hash, 2, &event_data)
+        }
+    }
+}
+
+/// Creates the hash 'num_hashes' after start_hash, plus an additional hash for any event data.
+pub fn next_hash<T: Serialize>(
+    start_hash: &Sha256Hash,
+    num_hashes: u64,
+    event: &Event<T>,
+) -> Sha256Hash {
+    let mut end_hash = *start_hash;
+    for _ in 0..num_hashes {
+        end_hash = hash(&end_hash);
+    }
+    hash_event(&end_hash, event)
+}
+
+/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
+pub fn next_entry<T: Serialize>(
+    start_hash: &Sha256Hash,
+    num_hashes: u64,
+    event: Event<T>,
+) -> Entry<T> {
+    Entry {
+        num_hashes,
+        end_hash: next_hash(start_hash, num_hashes, &event),
+        event,
+    }
+}
+
+/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
+pub fn next_entry_mut<T: Serialize>(
+    start_hash: &mut Sha256Hash,
+    num_hashes: u64,
+    event: Event<T>,
+) -> Entry<T> {
+    let entry = next_entry(start_hash, num_hashes, event);
+    *start_hash = entry.end_hash;
+    entry
+}
+
+/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
+pub fn next_tick<T: Serialize>(start_hash: &Sha256Hash, num_hashes: u64) -> Entry<T> {
+    next_entry(start_hash, num_hashes, Event::Tick)
+}
+
+pub fn verify_event<T: Serialize>(event: &Event<T>) -> bool {
+    use bincode::serialize;
+    if let Event::Claim { key, ref data, sig } = *event {
+        let mut claim_data = serialize(&data).unwrap();
+        if !verify_signature(&key, &claim_data, &sig) {
+            return false;
+        }
+    }
+    if let Event::Transaction {
+        from,
+        to,
+        ref data,
+        sig,
+    } = *event
+    {
+        let sign_data = serialize(&(&data, &to)).unwrap();
+        if !verify_signature(&from, &sign_data, &sig) {
+            return false;
+        }
+    }
+    true
+}
+
+/// Verifies self.end_hash is the result of hashing a 'start_hash' 'self.num_hashes' times.
+/// If the event is not a Tick, then hash that as well.
+pub fn verify_entry<T: Serialize>(entry: &Entry<T>, start_hash: &Sha256Hash) -> bool {
+    if !verify_event(&entry.event) {
+        return false;
+    }
+    entry.end_hash == next_hash(start_hash, entry.num_hashes, &entry.event)
+}
+
+/// Verifies the hashes and counts of a slice of events are all consistent.
+pub fn verify_slice(events: &[Entry<Sha256Hash>], start_hash: &Sha256Hash) -> bool {
+    use rayon::prelude::*;
+    let genesis = [Entry::new_tick(Default::default(), start_hash)];
+    let event_pairs = genesis.par_iter().chain(events).zip(events);
+    event_pairs.all(|(x0, x1)| verify_entry(&x1, &x0.end_hash))
+}
+
+/// Verifies the hashes and counts of a slice of events are all consistent.
+pub fn verify_slice_u64(events: &[Entry<u64>], start_hash: &Sha256Hash) -> bool {
+    use rayon::prelude::*;
+    let genesis = [Entry::new_tick(Default::default(), start_hash)];
+    let event_pairs = genesis.par_iter().chain(events).zip(events);
+    event_pairs.all(|(x0, x1)| verify_entry(&x1, &x0.end_hash))
+}
+
+/// Verifies the hashes and events serially. Exists only for reference.
+pub fn verify_slice_seq<T: Serialize>(events: &[Entry<T>], start_hash: &Sha256Hash) -> bool {
+    let genesis = [Entry::new_tick(0, start_hash)];
+    let mut event_pairs = genesis.iter().chain(events).zip(events);
+    event_pairs.all(|(x0, x1)| verify_entry(&x1, &x0.end_hash))
+}
+
+/// Verify a signed message with the given public key.
+pub fn verify_signature(peer_public_key_bytes: &[u8], msg_bytes: &[u8], sig_bytes: &[u8]) -> bool {
+    use untrusted;
+    use ring::signature;
+    let peer_public_key = untrusted::Input::from(peer_public_key_bytes);
+    let msg = untrusted::Input::from(msg_bytes);
+    let sig = untrusted::Input::from(sig_bytes);
+    signature::verify(&signature::ED25519, peer_public_key, msg, sig).is_ok()
+}
+
+pub fn create_entries<T: Serialize>(
+    start_hash: &Sha256Hash,
+    num_hashes: u64,
+    events: Vec<Event<T>>,
+) -> Vec<Entry<T>> {
+    let mut end_hash = *start_hash;
+    events
+        .into_iter()
+        .map(|event| next_entry_mut(&mut end_hash, num_hashes, event))
+        .collect()
+}
+
+/// Create a vector of Ticks of length 'len' from 'start_hash' hash and 'num_hashes'.
+pub fn create_ticks(
+    start_hash: &Sha256Hash,
+    num_hashes: u64,
+    len: usize,
+) -> Vec<Entry<Sha256Hash>> {
+    use std::iter;
+    let mut end_hash = *start_hash;
+    iter::repeat(Event::Tick)
+        .take(len)
+        .map(|event| next_entry_mut(&mut end_hash, num_hashes, event))
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_event_verify() {
+        let zero = Sha256Hash::default();
+        let one = hash(&zero);
+        assert!(verify_entry::<u8>(&Entry::new_tick(0, &zero), &zero)); // base case
+        assert!(!verify_entry::<u8>(&Entry::new_tick(0, &zero), &one)); // base case, bad
+        assert!(verify_entry::<u8>(&next_tick(&zero, 1), &zero)); // inductive step
+        assert!(!verify_entry::<u8>(&next_tick(&zero, 1), &one)); // inductive step, bad
+    }
+
+    #[test]
+    fn test_next_tick() {
+        let zero = Sha256Hash::default();
+        assert_eq!(next_tick::<Sha256Hash>(&zero, 1).num_hashes, 1)
+    }
+
+    fn verify_slice_generic(verify_slice: fn(&[Entry<Sha256Hash>], &Sha256Hash) -> bool) {
+        let zero = Sha256Hash::default();
+        let one = hash(&zero);
+        assert!(verify_slice(&vec![], &zero)); // base case
+        assert!(verify_slice(&vec![Entry::new_tick(0, &zero)], &zero)); // singleton case 1
+        assert!(!verify_slice(&vec![Entry::new_tick(0, &zero)], &one)); // singleton case 2, bad
+        assert!(verify_slice(&create_ticks(&zero, 0, 2), &zero)); // inductive step
+
+        let mut bad_ticks = create_ticks(&zero, 0, 2);
+        bad_ticks[1].end_hash = one;
+        assert!(!verify_slice(&bad_ticks, &zero)); // inductive step, bad
+    }
+
+    #[test]
+    fn test_verify_slice() {
+        verify_slice_generic(verify_slice);
+    }
+
+    #[test]
+    fn test_verify_slice_seq() {
+        verify_slice_generic(verify_slice_seq::<Sha256Hash>);
+    }
+
+    #[test]
+    fn test_reorder_attack() {
+        let zero = Sha256Hash::default();
+        let one = hash(&zero);
+
+        // First, verify Discovery events
+        let events = vec![
+            Event::Discovery { data: zero },
+            Event::Discovery { data: one },
+        ];
+        let mut entries = create_entries(&zero, 0, events);
+        assert!(verify_slice(&entries, &zero));
+
+        // Next, swap two Discovery events and ensure verification fails.
+        let event0 = entries[0].event.clone();
+        let event1 = entries[1].event.clone();
+        entries[0].event = event1;
+        entries[1].event = event0;
+        assert!(!verify_slice(&entries, &zero));
+    }
+
+    #[test]
+    fn test_claim() {
+        let keypair = generate_keypair();
+        let data = hash(b"hello, world");
+        let event0 = Event::Claim {
+            key: get_pubkey(&keypair),
+            data,
+            sig: sign_serialized(&data, &keypair),
+        };
+        let zero = Sha256Hash::default();
+        let entries = create_entries(&zero, 0, vec![event0]);
+        assert!(verify_slice(&entries, &zero));
+    }
+
+    #[test]
+    fn test_wrong_data_claim_attack() {
+        let keypair = generate_keypair();
+        let event0 = Event::Claim {
+            key: get_pubkey(&keypair),
+            data: hash(b"goodbye cruel world"),
+            sig: sign_serialized(&hash(b"hello, world"), &keypair),
+        };
+        let zero = Sha256Hash::default();
+        let entries = create_entries(&zero, 0, vec![event0]);
+        assert!(!verify_slice(&entries, &zero));
+    }
+
+    #[test]
+    fn test_transfer() {
+        let keypair0 = generate_keypair();
+        let keypair1 = generate_keypair();
+        let pubkey1 = get_pubkey(&keypair1);
+        let data = hash(b"hello, world");
+        let event0 = Event::Transaction {
+            from: get_pubkey(&keypair0),
+            to: pubkey1,
+            data,
+            sig: sign_transaction_data(&data, &keypair0, &pubkey1),
+        };
+        let zero = Sha256Hash::default();
+        let entries = create_entries(&zero, 0, vec![event0]);
+        assert!(verify_slice(&entries, &zero));
+    }
+
+    #[test]
+    fn test_wrong_data_transfer_attack() {
+        let keypair0 = generate_keypair();
+        let keypair1 = generate_keypair();
+        let pubkey1 = get_pubkey(&keypair1);
+        let data = hash(b"hello, world");
+        let event0 = Event::Transaction {
+            from: get_pubkey(&keypair0),
+            to: pubkey1,
+            data: hash(b"goodbye cruel world"), // <-- attack!
+            sig: sign_transaction_data(&data, &keypair0, &pubkey1),
+        };
+        let zero = Sha256Hash::default();
+        let entries = create_entries(&zero, 0, vec![event0]);
+        assert!(!verify_slice(&entries, &zero));
+    }
+
+    #[test]
+    fn test_transfer_hijack_attack() {
+        let keypair0 = generate_keypair();
+        let keypair1 = generate_keypair();
+        let thief_keypair = generate_keypair();
+        let pubkey1 = get_pubkey(&keypair1);
+        let data = hash(b"hello, world");
+        let event0 = Event::Transaction {
+            from: get_pubkey(&keypair0),
+            to: get_pubkey(&thief_keypair), // <-- attack!
+            data: hash(b"goodbye cruel world"),
+            sig: sign_transaction_data(&data, &keypair0, &pubkey1),
+        };
+        let zero = Sha256Hash::default();
+        let entries = create_entries(&zero, 0, vec![event0]);
+        assert!(!verify_slice(&entries, &zero));
+    }
+}
+
+#[cfg(all(feature = "unstable", test))]
+mod bench {
+    extern crate test;
+    use self::test::Bencher;
+    use log::*;
+
+    #[bench]
+    fn event_bench(bencher: &mut Bencher) {
+        let start_hash = Default::default();
+        let events = create_ticks(&start_hash, 10_000, 8);
+        bencher.iter(|| {
+            assert!(verify_slice(&events, &start_hash));
+        });
+    }
+
+    #[bench]
+    fn event_bench_seq(bencher: &mut Bencher) {
+        let start_hash = Default::default();
+        let events = create_ticks(&start_hash, 10_000, 8);
+        bencher.iter(|| {
+            assert!(verify_slice_seq(&events, &start_hash));
+        });
+    }
+}