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276 lines
11 KiB
Python
276 lines
11 KiB
Python
"""Create GPG ECDSA signatures and public keys using TREZOR device."""
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import base64
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import hashlib
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import logging
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import struct
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import time
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from . import agent, decode, proto
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from .. import client, factory, formats, util
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log = logging.getLogger(__name__)
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class HardwareSigner(object):
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"""Sign messages and get public keys from a hardware device."""
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def __init__(self, user_id, curve_name):
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"""Connect to the device and retrieve required public key."""
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self.client_wrapper = factory.load()
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self.identity = self.client_wrapper.identity_type()
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self.identity.proto = 'gpg'
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self.identity.host = user_id
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self.curve_name = curve_name
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def pubkey(self):
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"""Return public key as VerifyingKey object."""
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addr = client.get_address(self.identity)
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public_node = self.client_wrapper.connection.get_public_node(
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n=addr, ecdsa_curve_name=self.curve_name)
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return formats.decompress_pubkey(
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pubkey=public_node.node.public_key,
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curve_name=self.curve_name)
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def sign(self, digest):
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"""Sign the digest and return a serialized signature."""
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result = self.client_wrapper.connection.sign_identity(
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identity=self.identity,
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challenge_hidden=digest,
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challenge_visual=util.hexlify(digest),
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ecdsa_curve_name=self.curve_name)
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assert result.signature[:1] == b'\x00'
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sig = result.signature[1:]
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return (proto.mpi(util.bytes2num(sig[:32])) +
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proto.mpi(util.bytes2num(sig[32:])))
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def close(self):
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"""Close the connection to the device."""
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self.client_wrapper.connection.clear_session()
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self.client_wrapper.connection.close()
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class AgentSigner(object):
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"""Sign messages and get public keys using gpg-agent tool."""
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def __init__(self, user_id):
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"""Connect to the agent and retrieve required public key."""
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self.sock = agent.connect()
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self.keygrip = agent.get_keygrip(user_id)
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self.public_key = decode.load_from_gpg(user_id)
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def pubkey(self):
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"""Return public key as VerifyingKey object."""
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return self.public_key['verifying_key']
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def sign(self, digest):
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"""Sign the digest and return an ECDSA signature."""
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params = agent.sign(sock=self.sock,
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keygrip=self.keygrip, digest=digest)
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return b''.join(proto.mpi(p) for p in params)
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def close(self):
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"""Close the connection to gpg-agent."""
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self.sock.close()
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class PublicKey(object):
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"""GPG representation for public key packets."""
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def __init__(self, curve_name, created, verifying_key):
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"""Contruct using a ECDSA VerifyingKey object."""
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self.curve_info = proto.SUPPORTED_CURVES[curve_name]
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self.created = int(created) # time since Epoch
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self.verifying_key = verifying_key
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self.algo_id = self.curve_info['algo_id']
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def data(self):
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"""Data for packet creation."""
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header = struct.pack('>BLB',
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4, # version
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self.created, # creation
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self.algo_id) # public key algorithm ID
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oid = util.prefix_len('>B', self.curve_info['oid'])
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blob = self.curve_info['serialize'](self.verifying_key)
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return header + oid + blob
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def data_to_hash(self):
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"""Data for digest computation."""
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return b'\x99' + util.prefix_len('>H', self.data())
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def _fingerprint(self):
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return hashlib.sha1(self.data_to_hash()).digest()
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def key_id(self):
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"""Short (8 byte) GPG key ID."""
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return self._fingerprint()[-8:]
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def __repr__(self):
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"""Short (8 hexadecimal digits) GPG key ID."""
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return '<{}>'.format(util.hexlify(self.key_id()))
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__str__ = __repr__
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class Signer(object):
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"""Performs GPG signing operations."""
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def __init__(self, user_id, created, curve_name):
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"""Construct and loads a public key from the device."""
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self.user_id = user_id
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assert curve_name in formats.SUPPORTED_CURVES
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self.conn = HardwareSigner(user_id, curve_name=curve_name)
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self.pubkey = PublicKey(
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curve_name=curve_name, created=created,
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verifying_key=self.conn.pubkey())
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log.info('%s GPG public key %s created at %s for "%s"',
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curve_name, self.pubkey,
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util.time_format(self.pubkey.created), user_id)
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@classmethod
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def from_public_key(cls, pubkey, user_id):
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"""
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Create from an existing GPG public key.
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`pubkey` should be loaded via `decode.load_from_gpg(user_id)`
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from the local GPG keyring.
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"""
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s = Signer(user_id=user_id,
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created=pubkey['created'],
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curve_name=proto.find_curve_by_algo_id(pubkey['algo']))
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assert s.pubkey.key_id() == pubkey['key_id']
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return s
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def close(self):
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"""Close connection and turn off the screen of the device."""
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self.conn.close()
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def export(self):
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"""Export GPG public key, ready for "gpg2 --import"."""
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pubkey_packet = proto.packet(tag=6, blob=self.pubkey.data())
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user_id_packet = proto.packet(tag=13, blob=self.user_id)
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data_to_sign = (self.pubkey.data_to_hash() +
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user_id_packet[:1] +
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util.prefix_len('>L', self.user_id))
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log.info('signing public key "%s"', self.user_id)
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hashed_subpackets = [
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proto.subpacket_time(self.pubkey.created), # signature time
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proto.subpacket_byte(0x1B, 1 | 2), # key flags (certify & sign)
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proto.subpacket_byte(0x15, 8), # preferred hash (SHA256)
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proto.subpacket_byte(0x16, 0), # preferred compression (none)
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proto.subpacket_byte(0x17, 0x80)] # key server prefs (no-modify)
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unhashed_subpackets = [
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proto.subpacket(16, self.pubkey.key_id()), # issuer key id
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proto.CUSTOM_SUBPACKET]
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signature = _make_signature(
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signer_func=self.conn.sign,
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public_algo=self.pubkey.algo_id,
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data_to_sign=data_to_sign,
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sig_type=0x13, # user id & public key
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hashed_subpackets=hashed_subpackets,
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unhashed_subpackets=unhashed_subpackets)
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sign_packet = proto.packet(tag=2, blob=signature)
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return pubkey_packet + user_id_packet + sign_packet
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def subkey(self):
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"""Export a subkey to `self.user_id` GPG primary key."""
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subkey_packet = proto.packet(tag=14, blob=self.pubkey.data())
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primary = decode.load_from_gpg(self.user_id)
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log.info('adding subkey to primary GPG key "%s" (%s)',
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self.user_id, util.hexlify(primary['key_id']))
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data_to_sign = primary['_to_hash'] + self.pubkey.data_to_hash()
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# Primary Key Binding Signature
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hashed_subpackets = [
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proto.subpacket_time(self.pubkey.created)] # signature time
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unhashed_subpackets = [
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proto.subpacket(16, self.pubkey.key_id())] # issuer key id
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log.info('confirm signing subkey with hardware device')
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embedded_sig = _make_signature(signer_func=self.conn.sign,
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data_to_sign=data_to_sign,
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public_algo=self.pubkey.algo_id,
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sig_type=0x19,
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hashed_subpackets=hashed_subpackets,
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unhashed_subpackets=unhashed_subpackets)
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# Subkey Binding Signature
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hashed_subpackets = [
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proto.subpacket_time(self.pubkey.created), # signature time
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proto.subpacket_byte(0x1B, 2)] # key flags (certify & sign)
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unhashed_subpackets = [
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proto.subpacket(16, primary['key_id']), # issuer key id
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proto.subpacket(32, embedded_sig),
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proto.CUSTOM_SUBPACKET]
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log.info('confirm signing subkey with gpg-agent')
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gpg_agent = AgentSigner(self.user_id)
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signature = _make_signature(signer_func=gpg_agent.sign,
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data_to_sign=data_to_sign,
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public_algo=primary['algo'],
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sig_type=0x18,
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hashed_subpackets=hashed_subpackets,
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unhashed_subpackets=unhashed_subpackets)
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sign_packet = proto.packet(tag=2, blob=signature)
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return subkey_packet + sign_packet
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def sign(self, msg, sign_time=None):
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"""Sign GPG message at specified time."""
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if sign_time is None:
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sign_time = int(time.time())
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log.info('signing %d byte message at %s',
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len(msg), util.time_format(sign_time))
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hashed_subpackets = [proto.subpacket_time(sign_time)]
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unhashed_subpackets = [
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proto.subpacket(16, self.pubkey.key_id())] # issuer key id
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blob = _make_signature(signer_func=self.conn.sign,
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data_to_sign=msg,
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public_algo=self.pubkey.algo_id,
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hashed_subpackets=hashed_subpackets,
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unhashed_subpackets=unhashed_subpackets)
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return proto.packet(tag=2, blob=blob)
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def _make_signature(signer_func, data_to_sign, public_algo,
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hashed_subpackets, unhashed_subpackets, sig_type=0):
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# pylint: disable=too-many-arguments
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header = struct.pack('>BBBB',
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4, # version
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sig_type, # rfc4880 (section-5.2.1)
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public_algo,
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8) # hash_alg (SHA256)
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hashed = proto.subpackets(*hashed_subpackets)
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unhashed = proto.subpackets(*unhashed_subpackets)
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tail = b'\x04\xff' + struct.pack('>L', len(header) + len(hashed))
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data_to_hash = data_to_sign + header + hashed + tail
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log.debug('hashing %d bytes', len(data_to_hash))
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digest = hashlib.sha256(data_to_hash).digest()
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log.info('SHA256 digest to sign: %s', util.hexlify(digest))
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sig = signer_func(digest=digest)
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return bytes(header + hashed + unhashed +
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digest[:2] + # used for decoder's sanity check
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sig) # actual ECDSA signature
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def _split_lines(body, size):
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lines = []
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for i in range(0, len(body), size):
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lines.append(body[i:i+size] + '\n')
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return ''.join(lines)
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def armor(blob, type_str):
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"""See https://tools.ietf.org/html/rfc4880#section-6 for details."""
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head = '-----BEGIN PGP {}-----\nVersion: GnuPG v2\n\n'.format(type_str)
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body = base64.b64encode(blob)
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checksum = base64.b64encode(util.crc24(blob))
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tail = '-----END PGP {}-----\n'.format(type_str)
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return head + _split_lines(body, 64) + '=' + checksum + '\n' + tail
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