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

#[repr(C)]
pub struct BigModExpParams {
    pub base: *const u8,
    pub base_len: u64,
    pub exponent: *const u8,
    pub exponent_len: u64,
    pub modulus: *const u8,
    pub modulus_len: u64,
}

/// Big integer modular exponentiation
pub fn big_mod_exp(base: &[u8], exponent: &[u8], modulus: &[u8]) -> Vec<u8> {
    #[cfg(not(target_os = "solana"))]
    {
        use {
            num_bigint::BigUint,
            num_traits::{One, Zero},
        };

        let modulus_len = modulus.len();
        let base = BigUint::from_bytes_be(base);
        let exponent = BigUint::from_bytes_be(exponent);
        let modulus = BigUint::from_bytes_be(modulus);

        if modulus.is_zero() || modulus.is_one() {
            return vec![0_u8; modulus_len];
        }

        let ret_int = base.modpow(&exponent, &modulus);
        let ret_int = ret_int.to_bytes_be();
        let mut return_value = vec![0_u8; modulus_len.saturating_sub(ret_int.len())];
        return_value.extend(ret_int);
        return_value
    }

    #[cfg(target_os = "solana")]
    {
        let mut return_value = vec![0_u8; modulus.len()];

        let param = BigModExpParams {
            base: base as *const _ as *const u8,
            base_len: base.len() as u64,
            exponent: exponent as *const _ as *const u8,
            exponent_len: exponent.len() as u64,
            modulus: modulus as *const _ as *const u8,
            modulus_len: modulus.len() as u64,
        };
        unsafe {
            crate::syscalls::sol_big_mod_exp(
                &param as *const _ as *const u8,
                return_value.as_mut_slice() as *mut _ as *mut u8,
            )
        };

        return_value
    }
}

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

    #[test]
    fn big_mod_exp_test() {
        #[derive(serde::Deserialize)]
        #[serde(rename_all = "PascalCase")]
        struct TestCase {
            base: String,
            exponent: String,
            modulus: String,
            expected: String,
        }

        let test_data = r#"[
        {
            "Base":     "1111111111111111111111111111111111111111111111111111111111111111",
            "Exponent": "1111111111111111111111111111111111111111111111111111111111111111",
            "Modulus":  "111111111111111111111111111111111111111111111111111111111111110A",
            "Expected": "0A7074864588D6847F33A168209E516F60005A0CEC3F33AAF70E8002FE964BCD"
        },
        {
            "Base":     "2222222222222222222222222222222222222222222222222222222222222222",
            "Exponent": "2222222222222222222222222222222222222222222222222222222222222222",
            "Modulus":  "1111111111111111111111111111111111111111111111111111111111111111",
            "Expected": "0000000000000000000000000000000000000000000000000000000000000000"
        },
        {
            "Base":     "3333333333333333333333333333333333333333333333333333333333333333",
            "Exponent": "3333333333333333333333333333333333333333333333333333333333333333",
            "Modulus":  "2222222222222222222222222222222222222222222222222222222222222222",
            "Expected": "1111111111111111111111111111111111111111111111111111111111111111"
        },
        {
            "Base":     "9874231472317432847923174392874918237439287492374932871937289719",
            "Exponent": "0948403985401232889438579475812347232099080051356165126166266222",
            "Modulus":  "25532321a214321423124212222224222b242222222222222222222222222444",
            "Expected": "220ECE1C42624E98AEE7EB86578B2FE5C4855DFFACCB43CCBB708A3AB37F184D"
        },
        {
            "Base":     "3494396663463663636363662632666565656456646566786786676786768766",
            "Exponent": "2324324333246536456354655645656616169896565698987033121934984955",
            "Modulus":  "0218305479243590485092843590249879879842313131156656565565656566",
            "Expected": "012F2865E8B9E79B645FCE3A9E04156483AE1F9833F6BFCF86FCA38FC2D5BEF0"
        },
        {
            "Base":     "0000000000000000000000000000000000000000000000000000000000000005",
            "Exponent": "0000000000000000000000000000000000000000000000000000000000000002",
            "Modulus":  "0000000000000000000000000000000000000000000000000000000000000007",
            "Expected": "0000000000000000000000000000000000000000000000000000000000000004"
        },
        {
            "Base":     "0000000000000000000000000000000000000000000000000000000000000019",
            "Exponent": "0000000000000000000000000000000000000000000000000000000000000019",
            "Modulus":  "0000000000000000000000000000000000000000000000000000000000000064",
            "Expected": "0000000000000000000000000000000000000000000000000000000000000019"
        },
        {
            "Base":     "0000000000000000000000000000000000000000000000000000000000000019",
            "Exponent": "0000000000000000000000000000000000000000000000000000000000000019",
            "Modulus":  "0000000000000000000000000000000000000000000000000000000000000000",
            "Expected": "0000000000000000000000000000000000000000000000000000000000000000"
        },
        {
            "Base":     "0000000000000000000000000000000000000000000000000000000000000019",
            "Exponent": "0000000000000000000000000000000000000000000000000000000000000019",
            "Modulus":  "0000000000000000000000000000000000000000000000000000000000000001",
            "Expected": "0000000000000000000000000000000000000000000000000000000000000000"
        }
        ]"#;

        let test_cases: Vec<TestCase> = serde_json::from_str(test_data).unwrap();
        test_cases.iter().for_each(|test| {
            let base = array_bytes::hex2bytes_unchecked(&test.base);
            let exponent = array_bytes::hex2bytes_unchecked(&test.exponent);
            let modulus = array_bytes::hex2bytes_unchecked(&test.modulus);
            let expected = array_bytes::hex2bytes_unchecked(&test.expected);
            let result = big_mod_exp(base.as_slice(), exponent.as_slice(), modulus.as_slice());
            assert_eq!(result, expected);
        });
    }
}