trezor-agent/libagent/gpg/encode.py

"""Create GPG ECDSA signatures and public keys using TREZOR device."""
import io
import logging

from . import decode, keyring, protocol
from .. import util

log = logging.getLogger(__name__)


def create_primary(user_id, pubkey, signer_func, secret_bytes=b''):
    """Export new primary GPG public key, ready for "gpg2 --import"."""
    pubkey_packet = protocol.packet(tag=(5 if secret_bytes else 6),
                                    blob=(pubkey.data() + secret_bytes))
    user_id_bytes = user_id.encode('utf-8')
    user_id_packet = protocol.packet(tag=13, blob=user_id_bytes)
    data_to_sign = (pubkey.data_to_hash() + user_id_packet[:1] +
                    util.prefix_len('>L', user_id_bytes))
    hashed_subpackets = [
        protocol.subpacket_time(pubkey.created),  # signature time
        # https://tools.ietf.org/html/rfc4880#section-5.2.3.7
        protocol.subpacket_byte(0x0B, 9),  # preferred symmetric algo (AES-256)
        # https://tools.ietf.org/html/rfc4880#section-5.2.3.4
        protocol.subpacket_byte(0x1B, 1 | 2),  # key flags (certify & sign)
        # https://tools.ietf.org/html/rfc4880#section-5.2.3.21
        protocol.subpacket_bytes(0x15, [8, 9, 10]),  # preferred hash
        # https://tools.ietf.org/html/rfc4880#section-5.2.3.8
        protocol.subpacket_bytes(0x16, [2, 3, 1]),  # preferred compression
        # https://tools.ietf.org/html/rfc4880#section-5.2.3.9
        protocol.subpacket_byte(0x17, 0x80),  # key server prefs (no-modify)
        # https://tools.ietf.org/html/rfc4880#section-5.2.3.17
        protocol.subpacket_byte(0x1E, 0x01),  # advanced features (MDC)
        # https://tools.ietf.org/html/rfc4880#section-5.2.3.24
    ]
    unhashed_subpackets = [
        protocol.subpacket(16, pubkey.key_id()),  # issuer key id
        protocol.CUSTOM_SUBPACKET]

    signature = protocol.make_signature(
        signer_func=signer_func,
        public_algo=pubkey.algo_id,
        data_to_sign=data_to_sign,
        sig_type=0x13,  # user id & public key
        hashed_subpackets=hashed_subpackets,
        unhashed_subpackets=unhashed_subpackets)

    sign_packet = protocol.packet(tag=2, blob=signature)
    return pubkey_packet + user_id_packet + sign_packet


def create_subkey(primary_bytes, subkey, signer_func, secret_bytes=b''):
    """Export new subkey to GPG primary key."""
    subkey_packet = protocol.packet(tag=(7 if secret_bytes else 14),
                                    blob=(subkey.data() + secret_bytes))
    packets = list(decode.parse_packets(io.BytesIO(primary_bytes)))
    primary, user_id, signature = packets[:3]

    data_to_sign = primary['_to_hash'] + subkey.data_to_hash()

    if subkey.ecdh:
        embedded_sig = None
    else:
        # Primary Key Binding Signature
        hashed_subpackets = [
            protocol.subpacket_time(subkey.created)]  # signature time
        unhashed_subpackets = [
            protocol.subpacket(16, subkey.key_id())]  # issuer key id
        embedded_sig = protocol.make_signature(
            signer_func=signer_func,
            data_to_sign=data_to_sign,
            public_algo=subkey.algo_id,
            sig_type=0x19,
            hashed_subpackets=hashed_subpackets,
            unhashed_subpackets=unhashed_subpackets)

    # Subkey Binding Signature

    # Key flags: https://tools.ietf.org/html/rfc4880#section-5.2.3.21
    # (certify & sign)                   (encrypt)
    flags = (2) if (not subkey.ecdh) else (4 | 8)

    hashed_subpackets = [
        protocol.subpacket_time(subkey.created),  # signature time
        protocol.subpacket_byte(0x1B, flags)]

    unhashed_subpackets = []
    unhashed_subpackets.append(protocol.subpacket(16, primary['key_id']))
    if embedded_sig is not None:
        unhashed_subpackets.append(protocol.subpacket(32, embedded_sig))
    unhashed_subpackets.append(protocol.CUSTOM_SUBPACKET)

    if not decode.has_custom_subpacket(signature):
        signer_func = keyring.create_agent_signer(user_id['value'])

    signature = protocol.make_signature(
        signer_func=signer_func,
        data_to_sign=data_to_sign,
        public_algo=primary['algo'],
        sig_type=0x18,
        hashed_subpackets=hashed_subpackets,
        unhashed_subpackets=unhashed_subpackets)
    sign_packet = protocol.packet(tag=2, blob=signature)
    return primary_bytes + subkey_packet + sign_packet