bitwarden_crypto/keys/
utils.rs

1use std::{cmp::max, pin::Pin};
2
3use generic_array::GenericArray;
4use typenum::U32;
5
6use super::Aes256CbcHmacKey;
7use crate::{CryptoError, Result, util::hkdf_expand};
8
9/// Stretch the given key using HKDF.
10/// This can be either a kdf-derived key (PIN/Master password) or
11/// a random key from key connector
12pub(super) fn stretch_key(key: &Pin<Box<GenericArray<u8, U32>>>) -> Aes256CbcHmacKey {
13    Aes256CbcHmacKey {
14        // this is safe because the key length is always 32 bytes
15        enc_key: hkdf_expand(key, Some("enc")).expect("HKDF expand to succeed"),
16        mac_key: hkdf_expand(key, Some("mac")).expect("HKDF expand to succeed"),
17    }
18}
19
20/// Pads bytes to a minimum length using PKCS7-like padding.
21/// The last N bytes of the padded bytes all have the value N. Minimum of 1 padding byte. maximum of
22/// 255 bytes. For example, padded to size 4, the value 0,0 becomes 0,0,2,2.
23/// If the more than 255 bytes of padding is required, this will return an error.
24pub(crate) fn pad_bytes(bytes: &mut Vec<u8>, min_length: usize) -> Result<(), CryptoError> {
25    // at least 1 byte of padding is required
26    let pad_bytes = min_length.saturating_sub(bytes.len()).max(1);
27    // Since each byte represents the padding size, the maximum padding is 255.
28    // If more padding is required, this will return an error.
29    if pad_bytes > 255 {
30        return Err(CryptoError::InvalidPadding);
31    }
32    let padded_length = max(min_length, bytes.len() + 1);
33    bytes.resize(padded_length, pad_bytes as u8);
34    Ok(())
35}
36
37/// Unpads bytes that is padded using the PKCS7-like padding defined by [pad_bytes].
38/// The last N bytes of the padded bytes all have the value N. Minimum of 1 padding byte.
39/// For example, padded to size 4, the value 0,0 becomes 0,0,2,2.
40pub(crate) fn unpad_bytes(padded_bytes: &[u8]) -> Result<&[u8], CryptoError> {
41    let pad_len = *padded_bytes.last().ok_or(CryptoError::InvalidPadding)? as usize;
42    // The padding is at minimum 1 as noted in `pad_bytes`
43    if pad_len == 0 || pad_len > padded_bytes.len() {
44        return Err(CryptoError::InvalidPadding);
45    }
46    Ok(padded_bytes[..(padded_bytes.len() - pad_len)].as_ref())
47}
48
49#[cfg(test)]
50mod tests {
51    use super::*;
52
53    #[test]
54    fn test_stretch_kdf_key() {
55        let key = Box::pin(
56            [
57                31, 79, 104, 226, 150, 71, 177, 90, 194, 80, 172, 209, 17, 129, 132, 81, 138, 167,
58                69, 167, 254, 149, 2, 27, 39, 197, 64, 42, 22, 195, 86, 75,
59            ]
60            .into(),
61        );
62        let stretched = stretch_key(&key);
63
64        assert_eq!(
65            [
66                111, 31, 178, 45, 238, 152, 37, 114, 143, 215, 124, 83, 135, 173, 195, 23, 142,
67                134, 120, 249, 61, 132, 163, 182, 113, 197, 189, 204, 188, 21, 237, 96
68            ],
69            stretched.enc_key.as_slice()
70        );
71        assert_eq!(
72            [
73                221, 127, 206, 234, 101, 27, 202, 38, 86, 52, 34, 28, 78, 28, 185, 16, 48, 61, 127,
74                166, 209, 247, 194, 87, 232, 26, 48, 85, 193, 249, 179, 155
75            ],
76            stretched.mac_key.as_slice()
77        );
78    }
79
80    #[test]
81    fn test_pad_bytes_256_error() {
82        let mut bytes = vec![1u8; 0];
83        let result = pad_bytes(&mut bytes, 256);
84        assert!(matches!(result, Err(CryptoError::InvalidPadding)));
85    }
86
87    #[test]
88    fn test_pad_bytes_roundtrip() {
89        let original_bytes = vec![1u8; 10];
90        let mut cloned_bytes = original_bytes.clone();
91        let mut encoded_bytes = vec![1u8; 12];
92        encoded_bytes[10] = 2;
93        encoded_bytes[11] = 2;
94        pad_bytes(&mut cloned_bytes, 12).expect("Padding failed");
95        assert_eq!(encoded_bytes, cloned_bytes);
96        let unpadded_bytes = unpad_bytes(&cloned_bytes).unwrap();
97        assert_eq!(original_bytes, unpadded_bytes);
98    }
99
100    #[test]
101    fn test_pad_bytes_roundtrip_empty() {
102        let original_bytes = Vec::new();
103        let mut cloned_bytes = original_bytes.clone();
104        pad_bytes(&mut cloned_bytes, 32).expect("Padding failed");
105        let unpadded = unpad_bytes(&cloned_bytes).unwrap();
106        assert_eq!(Vec::<u8>::new(), unpadded);
107    }
108
109    #[test]
110    fn test_unpad_bytes_invalid_empty() {
111        let data: Vec<u8> = vec![];
112        let result = unpad_bytes(&data);
113        assert!(matches!(result, Err(CryptoError::InvalidPadding)));
114    }
115
116    #[test]
117    fn test_unpad_bytes_invalid_too_large() {
118        // Last byte is 5, but only 4 bytes in total
119        let data = vec![1, 2, 3, 5];
120        let result = unpad_bytes(&data);
121        assert!(matches!(result, Err(CryptoError::InvalidPadding)));
122    }
123
124    #[test]
125    fn test_unpad_bytes_invalid_0_padding() {
126        // Padding value of 0 is invalid
127        let data = vec![1, 2, 3, 0];
128        let result = unpad_bytes(&data);
129        assert!(matches!(result, Err(CryptoError::InvalidPadding)));
130    }
131
132    #[test]
133    fn test_pad_and_unpad_bytes_range_0_to_1024() {
134        let cases: Vec<_> = (0..=1024)
135            .flat_map(|data_size| (2..=1024).map(move |padding_size| (data_size, padding_size)))
136            .collect();
137
138        let data_larger_than_padding_cases: Vec<_> = cases
139            .clone()
140            .into_iter()
141            .filter(|(data_size, padding_size)| data_size > padding_size)
142            .collect();
143        for (data_size, padding_size) in data_larger_than_padding_cases {
144            let mut data: Vec<u8> = vec![0x12; data_size];
145            let original = data.clone();
146            pad_bytes(&mut data, padding_size).expect("Padding failed");
147            let unpadded = unpad_bytes(&data).expect("Unpadding failed");
148            assert_eq!(
149                unpadded, original,
150                "Failed at size {} and padding {}",
151                data_size, padding_size
152            );
153        }
154
155        let padding_larger_than_data_cases: Vec<_> = cases
156            .clone()
157            .into_iter()
158            .filter(|(data_size, padding_size)| {
159                data_size <= padding_size && (padding_size - data_size) <= 255
160            })
161            .collect();
162        for (data_size, padding_size) in padding_larger_than_data_cases {
163            println!(
164                "Testing data_size: {}, padding_size: {}",
165                data_size, padding_size
166            );
167            let data_original: Vec<u8> = vec![0x12; data_size];
168            let mut data = data_original.clone();
169
170            pad_bytes(&mut data, padding_size).expect("Padding failed");
171            let unpadded = unpad_bytes(&data).expect("Unpadding failed");
172            assert_eq!(
173                unpadded, data_original,
174                "Failed at size {} and padding {}",
175                data_size, padding_size
176            );
177        }
178
179        let padding_massively_larger_than_data_cases: Vec<_> = cases
180            .into_iter()
181            .filter(|(data_size, padding_size)| {
182                data_size <= padding_size && (padding_size - data_size) > 255
183            })
184            .collect();
185        for (data_size, padding_size) in padding_massively_larger_than_data_cases {
186            let mut data: Vec<u8> = vec![0x12; data_size];
187            let error = pad_bytes(&mut data, padding_size);
188            assert!(
189                matches!(error, Err(CryptoError::InvalidPadding)),
190                "Expected InvalidPadding error at size {} and padding {}, but got {:?}",
191                data_size,
192                padding_size,
193                error
194            );
195        }
196    }
197}
bitwarden_crypto/keys/utils.rs

bitwarden_crypto/keys/
utils.rs
