106 lines
3.2 KiB
Python
106 lines
3.2 KiB
Python
import io
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import binascii
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import logging
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from . import util
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from . import formats
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log = logging.getLogger(__name__)
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SSH_AGENTC_REQUEST_RSA_IDENTITIES = 1
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SSH_AGENT_RSA_IDENTITIES_ANSWER = 2
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SSH2_AGENTC_REQUEST_IDENTITIES = 11
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SSH2_AGENT_IDENTITIES_ANSWER = 12
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SSH2_AGENTC_SIGN_REQUEST = 13
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SSH2_AGENT_SIGN_RESPONSE = 14
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class Error(Exception):
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pass
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class BadSignature(Error):
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pass
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class MissingKey(Error):
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pass
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class Handler(object):
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def __init__(self, keys, signer):
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self.public_keys = keys
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self.signer = signer
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self.methods = {
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SSH_AGENTC_REQUEST_RSA_IDENTITIES: Handler.legacy_pubs,
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SSH2_AGENTC_REQUEST_IDENTITIES: self.list_pubs,
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SSH2_AGENTC_SIGN_REQUEST: self.sign_message,
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}
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def handle(self, msg):
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log.debug('request: %d bytes', len(msg))
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buf = io.BytesIO(msg)
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code, = util.recv(buf, '>B')
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method = self.methods[code]
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log.debug('calling %s()', method.__name__)
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reply = method(buf=buf)
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log.debug('reply: %d bytes', len(reply))
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return reply
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@staticmethod
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def legacy_pubs(buf):
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''' SSH v1 public keys are not supported '''
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assert not buf.read()
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code = util.pack('B', SSH_AGENT_RSA_IDENTITIES_ANSWER)
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num = util.pack('L', 0) # no SSH v1 keys
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return util.frame(code, num)
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def list_pubs(self, buf):
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''' SSH v2 public keys are serialized and returned. '''
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assert not buf.read()
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keys = self.public_keys
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code = util.pack('B', SSH2_AGENT_IDENTITIES_ANSWER)
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num = util.pack('L', len(keys))
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log.debug('available keys: %s', [k['name'] for k in keys])
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for i, k in enumerate(keys):
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log.debug('%2d) %s', i+1, k['fingerprint'])
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pubs = [util.frame(k['blob']) + util.frame(k['name']) for k in keys]
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return util.frame(code, num, *pubs)
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def sign_message(self, buf):
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''' SSH v2 public key authentication is performed. '''
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key = formats.parse_pubkey(util.read_frame(buf))
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log.debug('looking for %s', key['fingerprint'])
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blob = util.read_frame(buf)
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assert util.read_frame(buf) == b''
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assert not buf.read()
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for k in self.public_keys:
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if (k['fingerprint']) == (key['fingerprint']):
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log.debug('using key %r (%s)', k['name'], k['fingerprint'])
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key = k
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break
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else:
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raise MissingKey('key not found')
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log.debug('signing %d-byte blob', len(blob))
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label = key['name'].decode('ascii') # label should be a string
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signature = self.signer(label=label, blob=blob)
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log.debug('signature: %s', binascii.hexlify(signature))
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try:
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sig_bytes = key['verifier'](sig=signature, msg=blob)
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log.info('signature status: OK')
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except formats.ecdsa.BadSignatureError:
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log.exception('signature status: ERROR')
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raise BadSignature('invalid ECDSA signature')
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log.debug('signature size: %d bytes', len(sig_bytes))
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data = util.frame(util.frame(key['type']), util.frame(sig_bytes))
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code = util.pack('B', SSH2_AGENT_SIGN_RESPONSE)
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return util.frame(code, data)
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