Function decrypt_pq_resumed

src/dnscrypt.rs:195–239

Decrypt a resumed PQ query, validating its ticket and deriving the per-query key without a KEM decapsulation.

(
    wrapped_packet: &[u8],
    dnscrypt_encryption_params_set: &[Arc<DNSCryptEncryptionParams>],
    pq_ticket_key: &pq::TicketKey,
)

/// Decrypt a resumed PQ query, validating its ticket and deriving the
/// per-query key without a KEM decapsulation.
fn decrypt_pq_resumed(
    wrapped_packet: &[u8],
    dnscrypt_encryption_params_set: &[Arc<DNSCryptEncryptionParams>],
    pq_ticket_key: &pq::TicketKey,
) -> Result<(EncryptionParams, Vec<u8>), Error> {
    let magic = pq::PQ_RESUME_MAGIC.len();
    let nonce_size = DNSCRYPT_QUERY_NONCE_SIZE;
    ensure!(wrapped_packet.len() >= magic + 2, "Short resumed query");
    let ticket_len =
        u16::from_be_bytes([wrapped_packet[magic], wrapped_packet[magic + 1]]) as usize;
    let ticket_off = magic + 2;
    ensure!(
        wrapped_packet.len() >= ticket_off + ticket_len + nonce_size + DNSCRYPT_MAC_SIZE + DNS_HEADER_SIZE,
        "Short resumed query"
    );
    let ticket = &wrapped_packet[ticket_off..ticket_off + ticket_len];
    let client_nonce = &wrapped_packet[ticket_off + ticket_len..ticket_off + ticket_len + nonce_size];
    let encrypted_packet = &wrapped_packet[ticket_off + ticket_len + nonce_size..];

    let opened = pq::open_ticket(pq_ticket_key, ticket)?;
    let fields = pq::parse_ticket_plain(&opened)?;
    ensure!(fields.ticket_expiry > now(), "Expired ticket");
    ensure!(
        dnscrypt_encryption_params_set.iter().any(|p| p.pq().is_some_and(|pq| {
            pq.client_magic() == fields.client_magic && pq.es_version() == fields.es_version
        })),
        "Ticket does not match a current certificate"
    );

    let resumed_key =
        pq::resumed_shared_key(&fields.resume_secret, &fields.client_magic, client_nonce, ticket);
    let mut nonce = [0u8; DNSCRYPT_FULL_NONCE_SIZE];
    nonce[..nonce_size].copy_from_slice(client_nonce);
    let packet = resumed_key.decrypt(&nonce, encrypted_packet)?;
    debug!("PQ resumed query accepted (no decapsulation)");
    rand::rng().fill_bytes(&mut nonce[nonce_size..]);
    Ok((
        EncryptionParams::Pq {
            shared_key: resumed_key,
            nonce,
            control: Vec::new(),
        },
        packet,
    ))
}

pub fn encrypt(
    packet: Vec<u8>,