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MIT License
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This project is based on the sample VDF implementation at
https://github.com/Chia-Network/vdf-competition. This is licensed under the
Apache 2.0 License, which can be found in LICENSE-APACHE. It also carries the
following NOTICE file:
Chia vdf-toy
Copyright 2018 and onwards Chia Network Inc.
This product includes software developed at
Chia Network Inc (https://www.chia.net/).

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## What is a VDF?
A Verifiable Delay Function (VDF) is a function that requires substantial time to evaluate (even with a polynomial number of parallel processors) but can be very quickly verified as correct. VDFs can be used to construct randomness beacons with multiple applications in a distributed network environment. By introducing a time delay during evaluation, VDFs prevent malicious actors from influencing output. The output cannot be differentiated from a random number until the final result is computed.
See <https://eprint.iacr.org/2018/712.pdf> for more details.
A Verifiable Delay Function (VDF) is a function that requires substantial time
to evaluate (even with a polynomial number of parallel processors) but can be
very quickly verified as correct. VDFs can be used to construct randomness
beacons with multiple applications in a distributed network environment. By
introducing a time delay during evaluation, VDFs prevent malicious actors from
influencing output. The output cannot be differentiated from a random number
until the final result is computed. See <https://eprint.iacr.org/2018/712.pdf>
for more details.
## Description
This VDF implementation is written in Rust. We use class groups to implement 2 approaches.
This VDF implementation is written in Rust. The GMP library is used for
arithmetic and greatest common divisor (GCD) calculations. We use class groups
to implement the approaches described in the following papers:
1. [Simple Verifiable Delay Functions](https://eprint.iacr.org/2018/627.pdf). Pietrzak, 2018
2. [Efficient Verifiable Delay Functions](https://eprint.iacr.org/2018/623.pdf). Wesolowski, 2018
The chosen generator is (2, 1, c), where c is calculated from the provided
discriminant. A form is represented internally (a, b, c), with the
discriminant not being used in most omputations. This implementation performs
reduction is performed after every multiplication and squaring, as not doing so
did not give any gains in our benchmarks.
This repo includes three crates:
* `classgroup`: a class group implementation, as well as a trait for class groups.
* `vdf`: a Verifyable Delay Function (VDF) trait, as well as an implementation of that trait.
* `vdf-cli`: a command-line interface to the vdf crate. It also includes additional commands, which are deprecated and will be replaced by a CLI to the classgroup crate.
* `classgroup`: a class group implementation, as well as a trait for class
groups.
* `vdf`: a Verifyable Delay Function (VDF) trait, as well as an
implementation of that trait.
* `vdf-cli`: a command-line interface to the vdf crate. It also includes
additional commands, which are deprecated and will be replaced by a CLI to
the classgroup crate.
## Usage
- Install [Rust](https://doc.rust-lang.org/cargo/getting-started/installation.html). We (POA Networks) have tested the code with the latest stable, beta, and nightly versions of Rust. It may work with older versions, but this is not guaranteed.
- Install [Rust]. We (POA Networks) have tested the code with the latest
stable, beta, and nightly versions of Rust. It may work with older
versions, but this is not guaranteed.
- Install the [GNU Multiple Precision Library](https://gmplib.org/)
* On Debian and derivatives (including Ubuntu):
```sh
@ -35,6 +56,8 @@ This repo includes three crates:
```sh
$ git clone https://github.com/poanetwork/vdf.git
$ cargo install --path=vdf-cli
$ # or for the competition binary
$ cargo install --path=vdf-competition
```
### Command Line Interface
@ -44,9 +67,11 @@ To initiate, use the `vdf-cli` command followed by 2 arguments:
- _challenge_: byte string of arbitrary length
- _difficulty_: number of iterations, each iteration requires more time to evaluate
This generates the Weslowski proof of time. To generate the Pietrzak proof of time, pass `-tpietrzak`. For detailed usage information, run `vdf-cli --help`.
This generates the Weslowski proof of time. To generate the Pietrzak proof of
time, pass `-tpietrzak`. For detailed usage information, run `vdf-cli --help`.
Once complete you will see the output,returned as a `Vec<u8>`. The CLI tool hex-encodes its output.
Once complete you will see the output, returned as a `Vec<u8>`. The CLI tool
hex-encodes its output.
**Example**
@ -55,7 +80,8 @@ $ vdf-cli aa 100
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
```
To verify, use the `vdi-cli` command with the same arguments and include the output.
To verify, use the `vdi-cli` command with the same arguments and include the
output.
**Example**
@ -89,13 +115,20 @@ const CORRECT_SOLUTION: &[u8] =
\xdc\x42\x16\xbc\x16\xef\x7d\xac\x97\x0b\x0e\xe4\x6d\x69\x41\x6f\x9a\x9a\xce\xe6\x51\
\xd1\x58\xac\x64\x91\x5b";
fn main() {
let num_bits: u16 = 2048; // The length of the prime numbers generated, in bits.
let pietrzak_vdf = PietrzakVDFParams(num_bits).new();
assert_eq!(
&pietrzak_vdf.solve(b"\xaa", 100).unwrap()[..],
CORRECT_SOLUTION
);
assert!(pietrzak_vdf.verify(b"\xaa", 100, CORRECT_SOLUTION).is_ok());
// The length of the prime numbers generated, in bits.
let num_bits: u16 = 2048;
// An instance of the VDF. Instances can be used arbitrarily many times.
let pietrzak_vdf = PietrzakVDFParams(num_bits).new();
// Solve for the correct answer. This will take a minute or two.
assert_eq!(
&pietrzak_vdf.solve(b"\xaa", 10000).unwrap()[..],
CORRECT_SOLUTION
);
// Verify the answer. This should be far faster (less than a second).
assert!(pietrzak_vdf.verify(b"\xaa", 10000, CORRECT_SOLUTION).is_ok());
}
```
@ -111,7 +144,10 @@ Additional benchmarks are under development.
### Current Benchmarks
These were generated by `./bench.sh aadf`.
These were generated by `./bench.sh aadf`. Outliers could be due to preemption
by the OS and/or hypervisor. Changes are relative to the previous test run
done on the same machine. Since the previous run was done with different
settings and/or code than reported here, these changes are not meaningful.
```text
Benchmarking square with seed aadf: 512: Collecting 100 samples in estimated 5.0439 s (374k iteratio square with seed aadf: 512
@ -167,7 +203,21 @@ Found 13 outliers among 100 measurements (13.00%)
6 (6.00%) high severe
```
[Rust]: <https://doc.rust-lang.org/cargo/getting-started/installation.html>
## License
Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0) or MIT License (LICENSE-MIT) at your discretion.
Copyright 2018 Chia Network Inc and POA Networks Ltd.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
<http://www.apache.org/licenses/LICENSE-2.0>
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.