spg-crypto 7.37.3

Self-built cryptographic primitives for SPG: BLAKE3 hash, CRC32, no_std.
Documentation 
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

//! Base64 (RFC 4648 standard alphabet) — encode + decode.
//!
//! Used by SPG v4.8 SCRAM-SHA-256, which exchanges client/server
//! proofs in base64. We don't pull `base64` from crates.io to keep
//! the no-external-crypto-deps story intact — the implementation
//! is ~30 LOC and easy to test.

use alloc::string::String;
use alloc::vec::Vec;

const ALPHA: &[u8; 64] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

pub fn encode(input: &[u8]) -> String {
    let mut out = String::with_capacity(input.len().div_ceil(3) * 4);
    let mut chunks = input.chunks_exact(3);
    for chunk in &mut chunks {
        let n = (u32::from(chunk[0]) << 16) | (u32::from(chunk[1]) << 8) | u32::from(chunk[2]);
        out.push(ALPHA[((n >> 18) & 0x3f) as usize] as char);
        out.push(ALPHA[((n >> 12) & 0x3f) as usize] as char);
        out.push(ALPHA[((n >> 6) & 0x3f) as usize] as char);
        out.push(ALPHA[(n & 0x3f) as usize] as char);
    }
    let rem = chunks.remainder();
    if rem.len() == 1 {
        let n = u32::from(rem[0]) << 16;
        out.push(ALPHA[((n >> 18) & 0x3f) as usize] as char);
        out.push(ALPHA[((n >> 12) & 0x3f) as usize] as char);
        out.push('=');
        out.push('=');
    } else if rem.len() == 2 {
        let n = (u32::from(rem[0]) << 16) | (u32::from(rem[1]) << 8);
        out.push(ALPHA[((n >> 18) & 0x3f) as usize] as char);
        out.push(ALPHA[((n >> 12) & 0x3f) as usize] as char);
        out.push(ALPHA[((n >> 6) & 0x3f) as usize] as char);
        out.push('=');
    }
    out
}

#[derive(Debug, PartialEq, Eq)]
pub enum DecodeError {
    InvalidLength,
    InvalidChar(u8),
}

pub fn decode(input: &str) -> Result<Vec<u8>, DecodeError> {
    let bytes = input.as_bytes();
    if !bytes.len().is_multiple_of(4) {
        return Err(DecodeError::InvalidLength);
    }
    let mut out = Vec::with_capacity(bytes.len() / 4 * 3);
    for chunk in bytes.chunks_exact(4) {
        let mut quad = [0u32; 4];
        let mut padding = 0;
        for (i, &b) in chunk.iter().enumerate() {
            if b == b'=' {
                padding += 1;
                continue;
            }
            if padding > 0 {
                return Err(DecodeError::InvalidChar(b));
            }
            quad[i] = u32::from(decode_char(b)?);
        }
        let n = (quad[0] << 18) | (quad[1] << 12) | (quad[2] << 6) | quad[3];
        out.push((n >> 16) as u8);
        if padding < 2 {
            out.push((n >> 8) as u8);
        }
        if padding < 1 {
            out.push(n as u8);
        }
    }
    Ok(out)
}

fn decode_char(b: u8) -> Result<u8, DecodeError> {
    Ok(match b {
        b'A'..=b'Z' => b - b'A',
        b'a'..=b'z' => b - b'a' + 26,
        b'0'..=b'9' => b - b'0' + 52,
        b'+' => 62,
        b'/' => 63,
        other => return Err(DecodeError::InvalidChar(other)),
    })
}

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

    #[test]
    fn rfc4648_test_vectors() {
        assert_eq!(encode(b""), "");
        assert_eq!(encode(b"f"), "Zg==");
        assert_eq!(encode(b"fo"), "Zm8=");
        assert_eq!(encode(b"foo"), "Zm9v");
        assert_eq!(encode(b"foob"), "Zm9vYg==");
        assert_eq!(encode(b"fooba"), "Zm9vYmE=");
        assert_eq!(encode(b"foobar"), "Zm9vYmFy");
    }

    #[test]
    fn decode_round_trip() {
        for original in [
            b"".as_slice(),
            b"f",
            b"fo",
            b"foo",
            b"foob",
            b"fooba",
            b"foobar",
        ] {
            let encoded = encode(original);
            let decoded = decode(&encoded).unwrap();
            assert_eq!(decoded, original);
        }
    }

    #[test]
    fn decode_rejects_bad_length() {
        assert_eq!(decode("Zg=").unwrap_err(), DecodeError::InvalidLength);
    }

    #[test]
    fn decode_rejects_bad_chars() {
        let err = decode("Zm9v!Yg=").unwrap_err();
        assert!(matches!(
            err,
            DecodeError::InvalidLength | DecodeError::InvalidChar(_)
        ));
    }
}