Function decrypt_segment_envelope

nodedb-wal/src/crypto.rs:414–442

Decrypt a segment envelope produced by [`encrypt_segment_envelope`]. The caller supplies the expected `magic`; mismatches surface as [`WalError::EncryptionError`].

(
    key: &WalEncryptionKey,
    magic: &[u8; 4],
    blob: &[u8],
)

/// The caller supplies the expected `magic`; mismatches surface as
/// [`WalError::EncryptionError`].
pub fn decrypt_segment_envelope(
    key: &WalEncryptionKey,
    magic: &[u8; 4],
    blob: &[u8],
) -> Result<Vec<u8>> {
    if blob.len() < SEGMENT_ENVELOPE_MIN_SIZE {
        return Err(WalError::EncryptionError {
            detail: "encrypted envelope too short".into(),
        });
    }
    let preamble: [u8; SEGMENT_ENVELOPE_PREAMBLE_SIZE] = blob[..SEGMENT_ENVELOPE_PREAMBLE_SIZE]
        .try_into()
        .expect("slice is preamble size");
    if &preamble[0..4] != magic {
        return Err(WalError::EncryptionError {
            detail: "envelope preamble magic mismatch".into(),
        });
    }
    let version = u16::from_le_bytes([preamble[4], preamble[5]]);
    if version != SEGMENT_ENVELOPE_VERSION {
        return Err(WalError::EncryptionError {
            detail: format!("unsupported envelope preamble version {version}"),
        });
    }
    let mut epoch = [0u8; 4];
    epoch.copy_from_slice(&preamble[8..12]);
    let ciphertext = &blob[SEGMENT_ENVELOPE_PREAMBLE_SIZE..];
    key.decrypt_aad(&epoch, SEGMENT_ENVELOPE_NONCE_LSN, &preamble, ciphertext)
}

/// Derive a 12-byte nonce from an epoch and LSN.
///