def _buildPacket(payload, exitType, exitInfo, path1, path2, paddingPRNG=None, paranoia=0, suppressTag=0):
"""Helper method to create a message.
The following fields must be set:
payload: the intended exit payload. Must be 28K.
(exitType, exitInfo): the routing type and info for the final
node. (Ignored for reply messages; 'exitInfo' should
include the 20-byte decoding tag.)
path1: a sequence of ServerInfo objects, one for each node on
the first leg of the path.
path2:
EITHER
a sequence of ServerInfo objects, one for each node
on the second leg of the path.
OR
a ReplyBlock object.
The following fields are optional:
paddingPRNG: A pseudo-random number generator used to pad the headers.
If not provided, we use a counter-mode AES stream seeded from our
entropy source.
paranoia: If this is false, we use the padding PRNG to generate
header secrets too. Otherwise, we read all of our header secrets
from the true entropy source.
"""
assert len(payload) == PAYLOAD_LEN
reply = None
if isinstance(path2, ReplyBlock):
reply = path2
path2 = None
else:
if len(exitInfo) < TAG_LEN and not suppressTag:
raise MixError("Implausibly short exit info: %r" % exitInfo)
if exitType < MIN_EXIT_TYPE and exitType != DROP_TYPE:
raise MixError("Invalid exit type: %4x" % exitType)
checkPathLength(path1, path2, exitType, exitInfo, explicitSwap=(reply is None), suppressTag=suppressTag)
### SETUP CODE: let's handle all the variant cases.
# Set up the random number generators.
if paddingPRNG is None:
paddingPRNG = Crypto.getCommonPRNG()
if paranoia:
nHops = len(path1)
if path2:
nHops += len(path2)
secretRNG = Crypto.getTrueRNG()
else:
secretRNG = paddingPRNG
# Determine exit routing for path1.
if reply:
path1exittype = reply.routingType
path1exitinfo = reply.routingInfo
else:
path1exittype, path1exitinfo = path1[-1].getRoutingFor(path2[0], swap=1)
# Generate secrets for path1.
secrets1 = [secretRNG.getBytes(SECRET_LEN) for _ in path1]
if path2:
# Make secrets for header 2, and construct header 2. We do this before
# making header1 so that our rng won't be used for padding yet.
secrets2 = [secretRNG.getBytes(SECRET_LEN) for _ in range(len(path2))]
header2 = _buildHeader(path2, secrets2, exitType, exitInfo, paddingPRNG)
else:
secrets2 = None
header2 = reply.header
# Construct header1.
header1 = _buildHeader(path1, secrets1, path1exittype, path1exitinfo, paddingPRNG)
return _constructMessage(secrets1, secrets2, header1, header2, payload)
def _buildPacket(payload, exitType, exitInfo,
path1, path2, paddingPRNG=None, paranoia=0,
suppressTag=0):
"""Helper method to create a message.
The following fields must be set:
payload: the intended exit payload. Must be 28K.
(exitType, exitInfo): the routing type and info for the final
node. (Ignored for reply messages; 'exitInfo' should
include the 20-byte decoding tag.)
path1: a sequence of ServerInfo objects, one for each node on
the first leg of the path.
path2:
EITHER
a sequence of ServerInfo objects, one for each node
on the second leg of the path.
OR
a ReplyBlock object.
The following fields are optional:
paddingPRNG: A pseudo-random number generator used to pad the headers.
If not provided, we use a counter-mode AES stream seeded from our
entropy source.
paranoia: If this is false, we use the padding PRNG to generate
header secrets too. Otherwise, we read all of our header secrets
from the true entropy source.
"""
assert len(payload) == PAYLOAD_LEN
reply = None
if isinstance(path2, ReplyBlock):
reply = path2
path2 = None
else:
if len(exitInfo) < TAG_LEN and not suppressTag:
raise MixError("Implausibly short exit info: %r"%exitInfo)
if exitType < MIN_EXIT_TYPE and exitType != DROP_TYPE:
raise MixError("Invalid exit type: %4x"%exitType)
checkPathLength(path1, path2, exitType, exitInfo,
explicitSwap=(reply is None),
suppressTag=suppressTag)
### SETUP CODE: let's handle all the variant cases.
# Set up the random number generators.
if paddingPRNG is None:
paddingPRNG = Crypto.getCommonPRNG()
if paranoia:
nHops = len(path1)
if path2: nHops += len(path2)
secretRNG = Crypto.getTrueRNG()
else:
secretRNG = paddingPRNG
# Determine exit routing for path1.
if reply:
path1exittype = reply.routingType
path1exitinfo = reply.routingInfo
else:
path1exittype, path1exitinfo = path1[-1].getRoutingFor(path2[0],swap=1)
# Generate secrets for path1.
secrets1 = [ secretRNG.getBytes(SECRET_LEN) for _ in path1 ]
if path2:
# Make secrets for header 2, and construct header 2. We do this before
# making header1 so that our rng won't be used for padding yet.
secrets2 = [ secretRNG.getBytes(SECRET_LEN) for _ in range(len(path2))]
header2 = _buildHeader(path2,secrets2,exitType,exitInfo,paddingPRNG)
else:
secrets2 = None
header2 = reply.header
# Construct header1.
header1 = _buildHeader(path1,secrets1,path1exittype,path1exitinfo,
paddingPRNG)
return _constructMessage(secrets1, secrets2, header1, header2, payload)
