mirror of
https://github.com/romanz/amodem.git
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244 lines
8.4 KiB
Python
244 lines
8.4 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 client, factory, formats, util
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log = logging.getLogger(__name__)
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def packet(tag, blob):
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"""Create small GPG packet."""
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assert len(blob) < 256
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length_type = 0 # : 1 byte for length
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leading_byte = 0x80 | (tag << 2) | (length_type)
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return struct.pack('>B', leading_byte) + util.prefix_len('>B', blob)
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def subpacket(subpacket_type, fmt, *values):
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"""Create GPG subpacket."""
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blob = struct.pack(fmt, *values) if values else fmt
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return struct.pack('>B', subpacket_type) + blob
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def subpacket_long(subpacket_type, value):
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"""Create GPG subpacket with 32-bit unsigned integer."""
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return subpacket(subpacket_type, '>L', value)
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def subpacket_time(value):
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"""Create GPG subpacket with time in seconds (since Epoch)."""
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return subpacket_long(2, value)
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def subpacket_byte(subpacket_type, value):
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"""Create GPG subpacket with 8-bit unsigned integer."""
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return subpacket(subpacket_type, '>B', value)
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def subpackets(*items):
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"""Serialize several GPG subpackets."""
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prefixed = [util.prefix_len('>B', item) for item in items]
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return util.prefix_len('>H', b''.join(prefixed))
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def mpi(value):
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"""Serialize multipresicion integer using GPG format."""
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bits = value.bit_length()
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data_size = (bits + 7) // 8
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data_bytes = [0] * data_size
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for i in range(data_size):
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data_bytes[i] = value & 0xFF
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value = value >> 8
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data_bytes.reverse()
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return struct.pack('>H', bits) + bytearray(data_bytes)
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def _serialize_nist256(vk):
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return mpi((4 << 512) |
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(vk.pubkey.point.x() << 256) |
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(vk.pubkey.point.y()))
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def _serialize_ed25519(vk):
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return mpi((0x40 << 256) |
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util.bytes2num(vk.to_bytes()))
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SUPPORTED_CURVES = {
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formats.CURVE_NIST256: {
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# https://tools.ietf.org/html/rfc6637#section-11
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'oid': b'\x2A\x86\x48\xCE\x3D\x03\x01\x07',
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'algo_id': 19,
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'serialize': _serialize_nist256
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},
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formats.CURVE_ED25519: {
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'oid': b'\x2B\x06\x01\x04\x01\xDA\x47\x0F\x01',
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'algo_id': 22,
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'serialize': _serialize_ed25519
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}
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}
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def _find_curve_by_algo_id(algo_id):
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curve_name, = [name for name, info in SUPPORTED_CURVES.items()
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if info['algo_id'] == algo_id]
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return curve_name
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class Signer(object):
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"""Performs GPG operations with the TREZOR."""
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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.curve_name = curve_name
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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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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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self.verifying_key = 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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self.created = int(created)
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log.info('%s GPG public key %s created at %s', self.curve_name,
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self.hex_short_key_id(), util.time_format(self.created))
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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 `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=_find_curve_by_algo_id(pubkey['algo']))
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assert s.key_id() == pubkey['key_id']
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return s
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def _pubkey_data(self):
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curve_info = SUPPORTED_CURVES[self.curve_name]
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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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curve_info['algo_id'])
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oid = util.prefix_len('>B', curve_info['oid'])
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blob = curve_info['serialize'](self.verifying_key)
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return header + oid + blob
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def _pubkey_data_to_hash(self):
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return b'\x99' + util.prefix_len('>H', self._pubkey_data())
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def _fingerprint(self):
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return hashlib.sha1(self._pubkey_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 hex_short_key_id(self):
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"""Short (8 hexadecimal digits) GPG key ID."""
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return util.hexlify(self.key_id()[-4:])
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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.client_wrapper.connection.clear_session()
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self.client_wrapper.connection.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 = packet(tag=6, blob=self._pubkey_data())
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user_id_packet = 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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subpacket_time(self.created), # signature creaion time
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subpacket_byte(0x1B, 1 | 2), # key flags (certify & sign)
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subpacket_byte(0x15, 8), # preferred hash (SHA256)
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subpacket_byte(0x16, 0), # preferred compression (none)
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subpacket_byte(0x17, 0x80)] # key server prefs (no-modify)
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signature = self._make_signature(visual=self.hex_short_key_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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sign_packet = packet(tag=2, blob=signature)
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return pubkey_packet + user_id_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 = [subpacket_time(sign_time)]
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blob = self._make_signature(
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visual=self.hex_short_key_id(),
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data_to_sign=msg, hashed_subpackets=hashed_subpackets)
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return packet(tag=2, blob=blob)
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def _make_signature(self, visual, data_to_sign,
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hashed_subpackets, sig_type=0):
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curve_info = SUPPORTED_CURVES[self.curve_name]
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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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curve_info['algo_id'],
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8) # hash_alg (SHA256)
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hashed = subpackets(*hashed_subpackets)
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unhashed = subpackets(
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subpacket(16, self.key_id()) # issuer key id
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)
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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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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=visual,
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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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sig = mpi(util.bytes2num(sig[:32])) + mpi(util.bytes2num(sig[32:]))
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return (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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