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# $Id: asn1.py 23 2006-11-08 15:45:33Z dugsong $
"""Abstract Syntax Notation #1."""
import struct, time
import dpkt
# Type class
CLASSMASK = 0xc0
UNIVERSAL = 0x00
APPLICATION = 0x40
CONTEXT = 0x80
PRIVATE = 0xc0
# Constructed (vs. primitive)
CONSTRUCTED = 0x20
# Universal-class tags
TAGMASK = 0x1f
INTEGER = 2
BIT_STRING = 3 # arbitrary bit string
OCTET_STRING = 4 # arbitrary octet string
NULL = 5
OID = 6 # object identifier
SEQUENCE = 16 # ordered collection of types
SET = 17 # unordered collection of types
PRINT_STRING = 19 # printable string
T61_STRING = 20 # T.61 (8-bit) character string
IA5_STRING = 22 # ASCII
UTC_TIME = 23
def utctime(buf):
"""Convert ASN.1 UTCTime string to UTC float."""
yy = int(buf[:2])
mm = int(buf[2:4])
dd = int(buf[4:6])
hh = int(buf[6:8])
mm = int(buf[8:10])
try:
ss = int(buf[10:12])
buf = buf[12:]
except TypeError:
ss = 0
buf = buf[10:]
if buf[0] == '+':
hh -= int(buf[1:3])
mm -= int(buf[3:5])
elif buf[0] == '-':
hh += int(buf[1:3])
mm += int(buf[3:5])
return time.mktime((2000 + yy, mm, dd, hh, mm, ss, 0, 0, 0))
def decode(buf):
"""Sleazy ASN.1 decoder.
Return list of (id, value) tuples from ASN.1 BER/DER encoded buffer.
"""
msg = []
while buf:
t = ord(buf[0])
constructed = t & CONSTRUCTED
tag = t & TAGMASK
l = ord(buf[1])
c = 0
if constructed and l == 128:
# XXX - constructed, indefinite length
msg.append(t, decode(buf[2:]))
elif l >= 128:
c = l & 127
if c == 1:
l = ord(buf[2])
elif c == 2:
l = struct.unpack('>H', buf[2:4])[0]
elif c == 3:
l = struct.unpack('>I', buf[1:5])[0] & 0xfff
c = 2
elif c == 4:
l = struct.unpack('>I', buf[2:6])[0]
else:
# XXX - can be up to 127 bytes, but...
raise dpkt.UnpackError('excessive long-form ASN.1 length %d' % l)
# Skip type, length
buf = buf[2+c:]
# Parse content
if constructed:
msg.append((t, decode(buf)))
elif tag == INTEGER:
if l == 0:
n = 0
elif l == 1:
n = ord(buf[0])
elif l == 2:
n = struct.unpack('>H', buf[:2])[0]
elif l == 3:
n = struct.unpack('>I', buf[:4])[0] >> 8
elif l == 4:
n = struct.unpack('>I', buf[:4])[0]
else:
raise dpkt.UnpackError('excessive integer length > %d bytes' % l)
msg.append((t, n))
elif tag == UTC_TIME:
msg.append((t, utctime(buf[:l])))
else:
msg.append((t, buf[:l]))
# Skip content
buf = buf[l:]
return msg
if __name__ == '__main__':
import unittest
class ASN1TestCase(unittest.TestCase):
def test_asn1(self):
s = '0\x82\x02Q\x02\x01\x0bc\x82\x02J\x04xcn=Douglas J Song 1, ou=Information Technology Division, ou=Faculty and Staff, ou=People, o=University of Michigan, c=US\n\x01\x00\n\x01\x03\x02\x01\x00\x02\x01\x00\x01\x01\x00\x87\x0bobjectclass0\x82\x01\xb0\x04\rmemberOfGroup\x04\x03acl\x04\x02cn\x04\x05title\x04\rpostalAddress\x04\x0ftelephoneNumber\x04\x04mail\x04\x06member\x04\thomePhone\x04\x11homePostalAddress\x04\x0bobjectClass\x04\x0bdescription\x04\x18facsimileTelephoneNumber\x04\x05pager\x04\x03uid\x04\x0cuserPassword\x04\x08joinable\x04\x10associatedDomain\x04\x05owner\x04\x0erfc822ErrorsTo\x04\x08ErrorsTo\x04\x10rfc822RequestsTo\x04\nRequestsTo\x04\tmoderator\x04\nlabeledURL\x04\nonVacation\x04\x0fvacationMessage\x04\x05drink\x04\x0elastModifiedBy\x04\x10lastModifiedTime\x04\rmodifiersname\x04\x0fmodifytimestamp\x04\x0ccreatorsname\x04\x0fcreatetimestamp'
self.failUnless(decode(s) == [(48, [(2, 11), (99, [(4, 'cn=Douglas J Song 1, ou=Information Technology Division, ou=Faculty and Staff, ou=People, o=University of Michigan, c=US'), (10, '\x00'), (10, '\x03'), (2, 0), (2, 0), (1, '\x00'), (135, 'objectclass'), (48, [(4, 'memberOfGroup'), (4, 'acl'), (4, 'cn'), (4, 'title'), (4, 'postalAddress'), (4, 'telephoneNumber'), (4, 'mail'), (4, 'member'), (4, 'homePhone'), (4, 'homePostalAddress'), (4, 'objectClass'), (4, 'description'), (4, 'facsimileTelephoneNumber'), (4, 'pager'), (4, 'uid'), (4, 'userPassword'), (4, 'joinable'), (4, 'associatedDomain'), (4, 'owner'), (4, 'rfc822ErrorsTo'), (4, 'ErrorsTo'), (4, 'rfc822RequestsTo'), (4, 'RequestsTo'), (4, 'moderator'), (4, 'labeledURL'), (4, 'onVacation'), (4, 'vacationMessage'), (4, 'drink'), (4, 'lastModifiedBy'), (4, 'lastModifiedTime'), (4, 'modifiersname'), (4, 'modifytimestamp'), (4, 'creatorsname'), (4, 'createtimestamp')])])])])
unittest.main()
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