# Copyright (C) 2001 Tommi Virtanen
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of version 2.1 of the GNU Lesser General Public
# License as published by the Free Software Foundation.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""Pure, simple, BER encoding and decoding"""
# This BER library is currently aimed at supporting LDAP, thus
# the following restrictions from RFC2251 apply:
#
# (1) Only the definite form of length encoding will be used.
#
# (2) OCTET STRING values will be encoded in the primitive form
# only.
#
# (3) If the value of a BOOLEAN type is true, the encoding MUST have
# its contents octets set to hex "FF".
#
# (4) If a value of a type is its default value, it MUST be absent.
# Only some BOOLEAN and INTEGER types have default values in
# this protocol definition.
import string
# xxxxxxxx
# |/|\.../
# | | |
# | | tag
# | |
# | primitive (0) or structured (1)
# |
# class
CLASS_MASK = 0xc0
CLASS_UNIVERSAL = 0x00
CLASS_APPLICATION = 0x40
CLASS_CONTEXT = 0x80
CLASS_PRIVATE = 0xc0
STRUCTURED_MASK = 0x20
STRUCTURED = 0x20
NOT_STRUCTURED = 0x00
TAG_MASK = 0x1f
# LENGTH
# 0xxxxxxx = 0..127
# 1xxxxxxx = len is stored in the next 0xxxxxxx octets
# indefinite form not supported
[docs]class UnknownBERTag(Exception):
def __init__(self, tag, context):
Exception.__init__(self)
self.tag = tag
self.context = context
def __str__(self):
return "BERDecoderContext has no tag 0x%02x: %s" \
% (self.tag, self.context)
import UserList
[docs]def berDecodeLength(m, offset=0):
"""
Return a tuple of (length, lengthLength).
m must be atleast one byte long.
"""
l=ber2int(m[offset+0])
ll=1
if l&0x80:
ll=1+(l&0x7F)
need(m, offset+ll)
l=ber2int(m[offset+1:offset+ll], signed=0)
return (l, ll)
[docs]def int2berlen(i):
assert i>=0
e=int2ber(i, signed=False)
if i <= 127:
return e
else:
l=len(e)
assert l>0
assert l<=127
return chr(0x80|l) + e
[docs]def int2ber(i, signed=True):
encoded=''
while ((signed and (i>127 or i<-128))
or (not signed and (i>255))):
encoded=chr(i%256)+encoded
i=i>>8
encoded=chr(i%256)+encoded
return encoded
[docs]def ber2int(e, signed=True):
need(e, 1)
v=0L+ord(e[0])
if v&0x80 and signed:
v=v-256
for i in range(1, len(e)):
v=(v<<8) | ord(e[i])
return v
[docs]class BERBase:
tag = None
[docs] def identification(self):
return self.tag
def __init__(self, tag=None):
if tag is not None:
self.tag=tag
def __len__(self):
return len(str(self))
def __cmp__(self, other):
if isinstance(other, BERBase):
return cmp(str(self), str(other))
else:
return -1
def __eq__(self, other):
if isinstance(other, BERBase):
return str(self) == str(other)
else:
return False
def __ne__(self, other):
if isinstance(other, BERBase):
return str(self) != str(other)
else:
return False
[docs]class BERStructured(BERBase):
[docs] def identification(self):
return STRUCTURED|self.tag
[docs]class BERException(Exception): pass
[docs]class BERExceptionInsufficientData(Exception): pass
[docs]def need(buf, n):
d=n-len(buf)
if d>0:
raise BERExceptionInsufficientData, d
[docs]class BERInteger(BERBase):
tag = 0x02
value = None
[docs] def fromBER(klass, tag, content, berdecoder=None):
assert len(content)>0
value=ber2int(content)
r = klass(value=value, tag=tag)
return r
fromBER = classmethod(fromBER)
def __init__(self, value=None, tag=None):
"""Create a new BERInteger object.
value is an integer.
"""
BERBase.__init__(self, tag)
assert value is not None
self.value=value
def __str__(self):
encoded=int2ber(self.value)
return chr(self.identification()) \
+int2berlen(len(encoded)) \
+encoded
def __repr__(self):
if self.tag==self.__class__.tag:
return self.__class__.__name__+"(value=%r)"%self.value
else:
return self.__class__.__name__+"(value=%r, tag=%d)" \
%(self.value, self.tag)
[docs]class BEROctetString(BERBase):
tag = 0x04
value = None
[docs] def fromBER(klass, tag, content, berdecoder=None):
assert len(content)>=0
r = klass(value=content, tag=tag)
return r
fromBER = classmethod(fromBER)
def __init__(self, value=None, tag=None):
BERBase.__init__(self, tag)
assert value is not None
self.value=value
def __str__(self):
value = str(self.value)
return chr(self.identification()) \
+int2berlen(len(value)) \
+value
def __repr__(self):
if self.tag==self.__class__.tag:
return self.__class__.__name__+"(value=%s)" \
%repr(self.value)
else:
return self.__class__.__name__ \
+"(value=%s, tag=%d)" \
%(repr(self.value), self.tag)
[docs]class BERNull(BERBase):
tag = 0x05
[docs] def fromBER(klass, tag, content, berdecoder=None):
assert len(content) == 0
r = klass(tag=tag)
return r
fromBER = classmethod(fromBER)
def __init__(self, tag=None):
BERBase.__init__(self, tag)
def __str__(self):
return chr(self.identification())+chr(0)
def __repr__(self):
if self.tag==self.__class__.tag:
return self.__class__.__name__+"()"
else:
return self.__class__.__name__+"(tag=%d)"%self.tag
[docs]class BERBoolean(BERBase):
tag = 0x01
[docs] def fromBER(klass, tag, content, berdecoder=None):
assert len(content) > 0
value = ber2int(content)
r = klass(value=value, tag=tag)
return r
fromBER = classmethod(fromBER)
def __init__(self, value=None, tag=None):
"""Create a new BERInteger object.
value is an integer.
"""
BERBase.__init__(self, tag)
assert value is not None
if value:
value=0xFF
self.value=value
def __str__(self):
assert self.value==0 or self.value==0xFF
return chr(self.identification()) \
+int2berlen(1) \
+chr(self.value)
def __repr__(self):
if self.tag==self.__class__.tag:
return self.__class__.__name__+"(value=%d)"%self.value
else:
return self.__class__.__name__+"(value=%d, tag=%d)" \
%(self.value, self.tag)
[docs]class BEREnumerated(BERInteger):
tag = 0x0a
[docs]class BERSequence(BERStructured, UserList.UserList):
# TODO __getslice__ calls __init__ with no args.
tag = 0x10
[docs] def fromBER(klass, tag, content, berdecoder=None):
l = berDecodeMultiple(content, berdecoder)
r = klass(l, tag=tag)
return r
fromBER = classmethod(fromBER)
def __init__(self, value=None, tag=None):
BERStructured.__init__(self, tag)
UserList.UserList.__init__(self)
assert value is not None
self[:]=value
def __str__(self):
r=string.join(map(str, self.data), '')
return chr(self.identification())+int2berlen(len(r))+r
def __repr__(self):
if self.tag==self.__class__.tag:
return self.__class__.__name__+"(value=%s)"%repr(self.data)
else:
return self.__class__.__name__+"(value=%s, tag=%d)" \
%(repr(self.data), self.tag)
[docs]class BERSequenceOf(BERSequence):
pass
[docs]class BERSet(BERSequence):
tag = 0x11
pass
[docs]class BERDecoderContext:
Identities = {
BERInteger.tag: BERInteger,
BEROctetString.tag: BEROctetString,
BERNull.tag: BERNull,
BERBoolean.tag: BERBoolean,
BEREnumerated.tag: BEREnumerated,
BERSequence.tag: BERSequence,
BERSet.tag: BERSet,
}
def __init__(self, fallback=None, inherit=None):
self.fallback=fallback
self.inherit_context=inherit
[docs] def lookup_id(self, id):
try:
return self.Identities[id]
except KeyError:
if self.fallback:
return self.fallback.lookup_id(id)
else:
return None
[docs] def inherit(self):
return self.inherit_context or self
def __repr__(self):
identities = []
for tag, class_ in self.Identities.items():
identities.append('0x%02x: %s' % (tag, class_.__name__))
return "<"+self.__class__.__name__ \
+" identities={%s}" % ', '.join(identities) \
+" fallback="+repr(self.fallback) \
+" inherit="+repr(self.inherit_context) \
+">"
[docs]def berDecodeObject(context, m):
"""berDecodeObject(context, string) -> (berobject, bytesUsed)
berobject may be None.
"""
while m:
need(m, 2)
i=ber2int(m[0], signed=0)&(CLASS_MASK|TAG_MASK)
length, lenlen = berDecodeLength(m, offset=1)
need(m, 1+lenlen+length)
m2 = m[1+lenlen:1+lenlen+length]
berclass=context.lookup_id(i)
if berclass:
inh=context.inherit()
assert inh
r = berclass.fromBER(tag=i,
content=m2,
berdecoder=inh)
return (r, 1+lenlen+length)
else:
#raise UnknownBERTag, (i, context)
print str(UnknownBERTag(i, context)) #TODO
return (None, 1+lenlen+length)
return (None, 0)
[docs]def berDecodeMultiple(content, berdecoder):
"""berDecodeMultiple(content, berdecoder) -> [objects]
Decodes everything in content and returns a list of decoded
objects.
All of content will be decoded, and content must contain complete
BER objects.
"""
l = []
while content:
n, bytes = berDecodeObject(berdecoder, content)
if n is not None:
l.append(n)
assert bytes <= len(content)
content = content[bytes:]
return l
#TODO unimplemented classes are below:
#class BERObjectIdentifier(BERBase):
# tag = 0x06
# pass
#class BERIA5String(BERBase):
# tag = 0x16
# pass
#class BERPrintableString(BERBase):
# tag = 0x13
# pass
#class BERT61String(BERBase):
# tag = 0x14
# pass
#class BERUTCTime(BERBase):
# tag = 0x17
# pass
#class BERBitString(BERBase):
# tag = 0x03
# pass