ethqr_gen/
crc.rs

1// CRC-16-CCITT lookup table for fast calculation
2const CRC16_CCITT_TABLE: [u16; 256] = [
3    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a, 0xb16b,
4    0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
5    0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401,
6    0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
7    0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738,
8    0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
9    0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b, 0x5af5, 0x4ad4, 0x7ab7, 0x6a96,
10    0x1a71, 0x0a50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
11    0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd,
12    0xad2a, 0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
13    0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca, 0xa1eb,
14    0xd10c, 0xc12d, 0xf14e, 0xe16f, 0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
15    0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e, 0x02b1, 0x1290, 0x22f3, 0x32d2,
16    0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
17    0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799, 0x97b8,
18    0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
19    0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806, 0x6827,
20    0x18c0, 0x08e1, 0x3882, 0x28a3, 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
21    0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92, 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d,
22    0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
23    0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, 0x6e17, 0x7e36, 0x4e55, 0x5e74,
24    0x2e93, 0x3eb2, 0x0ed1, 0x1ef0,
25];
26
27/// Calculate CRC-16-CCITT checksum according to `EMVCo` specification
28///
29/// This function calculates the CRC-16 checksum using the CCITT polynomial (0x1021)
30/// with initial value 0xFFFF, as required by the `EMVCo` QR Code specification.
31///
32/// # Arguments
33/// * `data` - The string data to calculate CRC for
34///
35/// # Returns
36/// A 4-character uppercase hexadecimal string representing the CRC
37///
38/// # Examples
39///
40/// ```
41/// use ethqr_gen::crc::calculate_crc16;
42///
43/// let data = "000201010212020140001234567890120415534512345678901252045999530358654041.005802CN5914BEST TRANSPORT6009GUANGZHOU6304";
44/// assert_eq!(calculate_crc16(data), "A9AD");
45/// ```
46#[must_use]
47pub fn calculate_crc16(data: &str) -> String {
48    let mut crc: u16 = 0xFFFF;
49
50    for byte in data.bytes() {
51        let table_index = ((crc >> 8) ^ u16::from(byte)) & 0xFF;
52        crc = (crc << 8) ^ CRC16_CCITT_TABLE[table_index as usize];
53    }
54
55    // EMVCo specification requires the CRC to be formatted as 4-digit uppercase hex
56    format!("{crc:04X}")
57}
58
59/// Verify CRC of QR code string according to `EMVCo` specification
60///
61/// This function verifies that the CRC at the end of a QR code string matches
62/// the calculated CRC for the payload data.
63///
64/// # Arguments
65/// * `qr_string` - The complete QR code string including CRC
66///
67/// # Returns
68/// `true` if CRC is valid, `false` otherwise
69///
70/// # Examples
71///
72/// ```
73/// use ethqr_gen::crc::verify_crc;
74///
75/// let qr_string = "000201010212020140001234567890120415534512345678901252045999530358654041.005802CN5914BEST TRANSPORT6009GUANGZHOU6304A9AD";
76/// assert!(verify_crc(qr_string));
77/// ```
78#[must_use]
79pub fn verify_crc(qr_string: &str) -> bool {
80    if qr_string.len() < 8 {
81        return false;
82    }
83
84    // CRC should be the last 8 characters: 6304XXXX (tag 63, length 04, 4-char CRC)
85    let crc_tag_start = qr_string.len().saturating_sub(8);
86
87    // Verify CRC tag format
88    if &qr_string[crc_tag_start..crc_tag_start + 4] != "6304" {
89        return false;
90    }
91
92    // Extract the provided CRC
93    let provided_crc = &qr_string[crc_tag_start + 4..];
94
95    // Calculate CRC for everything except the CRC value itself
96    let payload_for_crc = &qr_string[..crc_tag_start + 4];
97    let calculated_crc = calculate_crc16(payload_for_crc);
98
99    // Compare CRCs (case-insensitive)
100    provided_crc.to_uppercase() == calculated_crc.to_uppercase()
101}
102
103#[cfg(test)]
104mod tests {
105    use super::*;
106
107    #[test]
108    fn test_crc_calculation() {
109        // Test with known EMVCo example data
110        let test_data = "000201010212020140001234567890120415534512345678901252045999530358654041.005802CN5914BEST TRANSPORT6009GUANGZHOU6304";
111        let crc = calculate_crc16(test_data);
112
113        // Verify CRC format
114        assert_eq!(crc.len(), 4);
115        assert!(crc.chars().all(|c| c.is_ascii_hexdigit()));
116
117        // Test the complete verification process
118        let complete_qr = format!("{test_data}{crc}");
119        assert!(verify_crc(&complete_qr));
120    }
121
122    #[test]
123    fn test_crc_verification() {
124        // Test with simple data
125        let payload = "00020101121502014000123456789012345260116304";
126        let crc = calculate_crc16(payload);
127        let complete_qr = format!("{payload}{crc}");
128
129        // Should pass CRC verification
130        assert!(verify_crc(&complete_qr));
131
132        // Corrupted QR should fail verification
133        let mut corrupted = complete_qr.clone();
134        corrupted.pop(); // Remove last character
135        corrupted.push('X'); // Replace with wrong character
136        assert!(!verify_crc(&corrupted));
137    }
138
139    #[test]
140    fn test_empty_and_invalid_input() {
141        // Empty string should fail
142        assert!(!verify_crc(""));
143
144        // Too short string should fail
145        assert!(!verify_crc("1234567"));
146
147        // String without proper CRC tag should fail
148        assert!(!verify_crc("12345678901234567890"));
149    }
150}
ethqr_gen/crc.rs

ethqr_gen/
crc.rs
