bitwarden_crypto/keys/
prf.rs

1use crate::{CryptoError, SymmetricCryptoKey, utils::stretch_key};
2
3/// Takes the output of a PRF and derives a symmetric key.
4///
5/// The PRF output must be at least 32 bytes long. If longer, only the first 32
6/// bytes will be used, and the remainder is discarded.
7pub fn derive_symmetric_key_from_prf(prf: &[u8]) -> Result<SymmetricCryptoKey, CryptoError> {
8    let (secret, _) = prf.split_at_checked(32).ok_or(CryptoError::InvalidKeyLen)?;
9    let secret: [u8; 32] = secret.try_into().expect("length to be 32 bytes");
10    // Don't allow uninitialized PRFs
11    if secret.iter().all(|b| *b == b'\0') {
12        return Err(CryptoError::ZeroNumber);
13    }
14    Ok(SymmetricCryptoKey::Aes256CbcHmacKey(stretch_key(
15        &Box::pin(secret.into()),
16    )?))
17}
18
19#[cfg(test)]
20mod tests {
21    use super::*;
22
23    #[test]
24    fn test_prf_succeeds() {
25        let prf = pseudorandom_bytes(32);
26        let key = derive_symmetric_key_from_prf(&prf).unwrap();
27        assert!(matches!(key, SymmetricCryptoKey::Aes256CbcHmacKey(_)));
28    }
29
30    #[test]
31    fn test_zero_key_fails() {
32        let prf: Vec<u8> = (0..32).map(|_| 0).collect();
33        let err = derive_symmetric_key_from_prf(&prf).unwrap_err();
34        assert!(matches!(err, CryptoError::ZeroNumber));
35    }
36
37    #[test]
38    fn test_short_prf_fails() {
39        let prf = pseudorandom_bytes(9);
40        let err = derive_symmetric_key_from_prf(&prf).unwrap_err();
41        assert!(matches!(err, CryptoError::InvalidKeyLen));
42    }
43
44    #[test]
45    fn test_long_prf_truncated_to_proper_length() {
46        let long_prf = pseudorandom_bytes(33);
47        let prf = pseudorandom_bytes(32);
48        let key1 = derive_symmetric_key_from_prf(&long_prf).unwrap();
49        let key2 = derive_symmetric_key_from_prf(&prf).unwrap();
50        assert_eq!(key1, key2);
51    }
52
53    /// This returns the same bytes deterministically for a given length.
54    fn pseudorandom_bytes(len: usize) -> Vec<u8> {
55        (0..len).map(|x| (x % 255) as u8).collect()
56    }
57}
bitwarden_crypto/keys/prf.rs

bitwarden_crypto/keys/
prf.rs
