1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
//! MCaptch's SHA256 based Proof of Work library
//!
//! # Example:
//! ```rust
//!   use pow_sha256::{ConfigBuilder, PoW};
//!
//!   fn main() {
//!       let config = ConfigBuilder::default()
//!         .salt("myrandomsaltisnotlongenoug".into())
//!         .build()
//!         .unwrap();
//!
//!       let phrase = "ironmansucks";
//!
//!       const DIFFICULTY: u128 = u128::MAX / 32;
//!
//!       let work = config.prove_work(&phrase, DIFFICULTY).unwrap();
//!       assert!(config.calculate(&work, &phrase).unwrap() >= DIFFICULTY);
//!       assert!(config.is_valid_proof(&work, &phrase));
//!       assert!(config.is_sufficient_difficulty(&work, DIFFICULTY));
//!   }    
//! ```

use std::marker::PhantomData;

use derive_builder::Builder;
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};

/// Proof of Work over concrete type T. T can be any type that implements serde::Serialize.
#[derive(Serialize, Builder, Deserialize, PartialEq, Clone, Debug)]
pub struct PoW<T> {
    pub nonce: u64,
    pub result: String,
    #[builder(default = "PhantomData", setter(skip))]
    _spook: PhantomData<T>,
}

/// Configuration for generting proof of work
/// Please choose a long, unique value for salt
/// Resistance to dictionary/rainbow attacks depend on uniqueness
/// of the salt
#[derive(Serialize, Deserialize, Builder, PartialEq, Clone, Debug)]
pub struct Config {
    pub salt: String,
}

impl Config {
    /// Create Proof of Work over item of type T.
    ///
    /// Make sure difficulty is not too high. A 64 bit difficulty,
    /// for example, takes a long time on a general purpose processor.
    /// Returns bincode::Error if serialization fails.
    pub fn prove_work<T>(&self, t: &T, difficulty: u128) -> bincode::Result<PoW<T>>
    where
        T: Serialize,
    {
        bincode::serialize(t).map(|v| self.prove_work_serialized(&v, difficulty))
    }

    /// Create Proof of Work on an already serialized item of type T.
    /// The input is assumed to be serialized using network byte order.
    ///
    /// Make sure difficulty is not too high. A 64 bit difficulty,
    /// for example, takes a long time on a general purpose processor.
    pub fn prove_work_serialized<T>(&self, prefix: &[u8], difficulty: u128) -> PoW<T>
    where
        T: Serialize,
    {
        let prefix_sha = Sha256::new().chain(&self.salt).chain(prefix);
        let mut n = 0;
        let mut result = 0;
        while result < difficulty {
            n += 1;
            result = score(prefix_sha.clone(), n);
        }
        PoW {
            nonce: n,
            result: result.to_string(),
            _spook: PhantomData,
        }
    }

    /// Calculate the PoW score with the provided input T.
    pub fn calculate<T>(&self, pow: &PoW<T>, t: &T) -> bincode::Result<u128>
    where
        T: Serialize,
    {
        bincode::serialize(t).map(|v| self.calculate_serialized(pow, &v))
    }

    /// Calculate the PoW score of an already serialized T and self.
    /// The input is assumed to be serialized using network byte order.
    pub fn calculate_serialized<T>(&self, pow: &PoW<T>, target: &[u8]) -> u128
    where
        T: Serialize,
    {
        score(Sha256::new().chain(&self.salt).chain(target), pow.nonce)
    }

    /// Verifies that the PoW is indeed generated out of the phrase provided.
    pub fn is_valid_proof<T>(&self, pow: &PoW<T>, t: &T) -> bool
    where
        T: Serialize,
    {
        match self.calculate(pow, t) {
            Ok(res) => {
                return if pow.result == res.to_string() {
                    true
                } else {
                    false
                }
            }
            Err(_) => return false,
        }
    }

    /// Checks if the PoW result is of sufficient difficulty
    pub fn is_sufficient_difficulty<T>(&self, pow: &PoW<T>, target_diff: u128) -> bool
    where
        T: Serialize,
    {
        match pow.result.parse::<u128>() {
            Ok(res) => return res >= target_diff,
            Err(_) => return false,
        }
    }
}

fn score(prefix_sha: Sha256, nonce: u64) -> u128 {
    first_bytes_as_u128(
        prefix_sha
            .chain(&nonce.to_be_bytes()) // to_be_bytes() converts to network endian
            .finalize()
            .as_slice(),
    )
}

/// # Panics
///
/// panics if inp.len() < 16
fn first_bytes_as_u128(inp: &[u8]) -> u128 {
    bincode::deserialize(&inp).unwrap()
}

#[cfg(test)]
mod test {
    use super::*;

    const DIFFICULTY: u128 = 0xff000000000000000000000000000000;

    fn get_config() -> Config {
        ConfigBuilder::default()
            .salt(
                "79ziepia7vhjgviiwjhnend3ofjqocsi2winc4ptqhmkvcajihywxcizewvckg9h6gs4j83v9".into(),
            )
            .build()
            .unwrap()
    }

    #[test]
    fn base_functionality() {
        // Let's prove we did work targeting a phrase.
        let phrase = b"Ex nihilo nihil fit.".to_vec();
        let config = get_config();
        let pw = config.prove_work(&phrase, DIFFICULTY).unwrap();
        assert!(config.calculate(&pw, &phrase).unwrap() >= DIFFICULTY);
        assert!(config.is_valid_proof(&pw, &phrase));
        assert!(config.is_sufficient_difficulty(&pw, DIFFICULTY));
    }

    #[test]
    fn double_pow() {
        let phrase = "Ex nihilo nihil fit.".to_owned();
        let config = get_config();

        let pw = config.prove_work(&phrase, DIFFICULTY).unwrap();
        let pwpw = config.prove_work(&pw, DIFFICULTY).unwrap();

        assert!(config.calculate(&pw, &phrase).unwrap() >= DIFFICULTY);
        assert!(config.is_valid_proof(&pw, &phrase));
        assert!(config.is_sufficient_difficulty(&pw, DIFFICULTY));

        assert!(config.calculate(&pwpw, &pw).unwrap() >= DIFFICULTY);
        assert!(config.is_valid_proof(&pwpw, &pw));
        assert!(config.is_sufficient_difficulty(&pwpw, DIFFICULTY));
    }

    #[test]
    fn is_not_valid_proof() {
        let phrase = "Ex nihilo nihil fit.".to_owned();
        let phrase2 = "Omne quod movetur ab alio movetur.".to_owned();

        let config = get_config();
        let pw = config.prove_work(&phrase, DIFFICULTY).unwrap();

        let pw2 = config.prove_work(&phrase2, DIFFICULTY).unwrap();

        assert!(!config.is_valid_proof(&pw, &phrase2));
        assert!(!config.is_valid_proof(&pw2, &phrase));
    }

    #[test]
    fn serialization_test() {
        let target: u8 = 1;
        let config = get_config();
        let pw = config.prove_work(&target, DIFFICULTY).unwrap();

        let message: (u8, PoW<u8>) = (target, pw);
        let message_ser = bincode::serialize(&message).unwrap();
        let recieved_message: (u8, PoW<u8>) = bincode::deserialize(&message_ser).unwrap();
        assert_eq!(recieved_message, message);
        assert!(config.is_sufficient_difficulty(&message.1, DIFFICULTY));
        assert!(config.is_valid_proof(&message.1, &target));
    }
}