ASN.1 (Abstract Syntax Notation One) DER (Distinguished Encoding Rules) is a standard-backed serialization scheme used in many different use-cases. Particularly popular usage scenarios are X.509 certificates and some telecommunication / networking protocols.
DER is self-describing encoding scheme which allows representation of simple, atomic data elements, such as strings and numbers, and complex objects, such as sequences of other elements.
DER is a subset of BER (Basic Encoding Rules), with an emphasis on being non-ambiguous: there's always exactly one canonical way to encode a data structure defined in terms of ASN.1 using DER.
This spec allows full parsing of format syntax, but to understand the semantics, one would typically require a dictionary of Object Identifiers (OIDs), to match OID bodies against some human-readable list of constants. OIDs are covered by many different standards, so typically it's simpler to use a pre-compiled list of them, such as:
This page hosts a formal specification of ASN.1 DER (Abstract Syntax Notation One, Distinguished Encoding Rules) using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for Python generated by Kaitai Struct depends on the Python runtime library. You have to install it before you can parse data.
The Python runtime library can be installed from PyPI:
python3 -m pip install kaitaistructParse a local file and get structure in memory:
data = Asn1Der.from_file("path/to/local/file.der")
Or parse structure from a bytes:
from kaitaistruct import KaitaiStream, BytesIO
raw = b"\x00\x01\x02..."
data = Asn1Der(KaitaiStream(BytesIO(raw)))
After that, one can get various attributes from the structure by invoking getter methods like:
data.type_tag # => get type tag
# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
import kaitaistruct
from kaitaistruct import KaitaiStruct, KaitaiStream, BytesIO
from enum import Enum
if getattr(kaitaistruct, 'API_VERSION', (0, 9)) < (0, 9):
raise Exception("Incompatible Kaitai Struct Python API: 0.9 or later is required, but you have %s" % (kaitaistruct.__version__))
class Asn1Der(KaitaiStruct):
"""ASN.1 (Abstract Syntax Notation One) DER (Distinguished Encoding
Rules) is a standard-backed serialization scheme used in many
different use-cases. Particularly popular usage scenarios are X.509
certificates and some telecommunication / networking protocols.
DER is self-describing encoding scheme which allows representation
of simple, atomic data elements, such as strings and numbers, and
complex objects, such as sequences of other elements.
DER is a subset of BER (Basic Encoding Rules), with an emphasis on
being non-ambiguous: there's always exactly one canonical way to
encode a data structure defined in terms of ASN.1 using DER.
This spec allows full parsing of format syntax, but to understand
the semantics, one would typically require a dictionary of Object
Identifiers (OIDs), to match OID bodies against some human-readable
list of constants. OIDs are covered by many different standards,
so typically it's simpler to use a pre-compiled list of them, such
as:
* <https://www.cs.auckland.ac.nz/~pgut001/dumpasn1.cfg>
* <http://oid-info.com/>
* <https://www.alvestrand.no/objectid/top.html>
.. seealso::
Source - https://www.itu.int/itu-t/recommendations/rec.aspx?rec=12483&lang=en
"""
class TypeTag(Enum):
end_of_content = 0
boolean = 1
integer = 2
bit_string = 3
octet_string = 4
null_value = 5
object_id = 6
object_descriptor = 7
external = 8
real = 9
enumerated = 10
embedded_pdv = 11
utf8string = 12
relative_oid = 13
sequence_10 = 16
printable_string = 19
ia5string = 22
sequence_30 = 48
set = 49
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self.type_tag = KaitaiStream.resolve_enum(Asn1Der.TypeTag, self._io.read_u1())
self.len = Asn1Der.LenEncoded(self._io, self, self._root)
_on = self.type_tag
if _on == Asn1Der.TypeTag.printable_string:
self._raw_body = self._io.read_bytes(self.len.result)
_io__raw_body = KaitaiStream(BytesIO(self._raw_body))
self.body = Asn1Der.BodyPrintableString(_io__raw_body, self, self._root)
elif _on == Asn1Der.TypeTag.sequence_10:
self._raw_body = self._io.read_bytes(self.len.result)
_io__raw_body = KaitaiStream(BytesIO(self._raw_body))
self.body = Asn1Der.BodySequence(_io__raw_body, self, self._root)
elif _on == Asn1Der.TypeTag.set:
self._raw_body = self._io.read_bytes(self.len.result)
_io__raw_body = KaitaiStream(BytesIO(self._raw_body))
self.body = Asn1Der.BodySequence(_io__raw_body, self, self._root)
elif _on == Asn1Der.TypeTag.sequence_30:
self._raw_body = self._io.read_bytes(self.len.result)
_io__raw_body = KaitaiStream(BytesIO(self._raw_body))
self.body = Asn1Der.BodySequence(_io__raw_body, self, self._root)
elif _on == Asn1Der.TypeTag.utf8string:
self._raw_body = self._io.read_bytes(self.len.result)
_io__raw_body = KaitaiStream(BytesIO(self._raw_body))
self.body = Asn1Der.BodyUtf8string(_io__raw_body, self, self._root)
elif _on == Asn1Der.TypeTag.object_id:
self._raw_body = self._io.read_bytes(self.len.result)
_io__raw_body = KaitaiStream(BytesIO(self._raw_body))
self.body = Asn1Der.BodyObjectId(_io__raw_body, self, self._root)
else:
self.body = self._io.read_bytes(self.len.result)
class BodySequence(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self.entries = []
i = 0
while not self._io.is_eof():
self.entries.append(Asn1Der(self._io))
i += 1
class BodyUtf8string(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self.str = (self._io.read_bytes_full()).decode(u"UTF-8")
class BodyObjectId(KaitaiStruct):
"""
.. seealso::
Source - https://learn.microsoft.com/en-us/windows/win32/seccertenroll/about-object-identifier
"""
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self.first_and_second = self._io.read_u1()
self.rest = self._io.read_bytes_full()
@property
def first(self):
if hasattr(self, '_m_first'):
return self._m_first
self._m_first = self.first_and_second // 40
return getattr(self, '_m_first', None)
@property
def second(self):
if hasattr(self, '_m_second'):
return self._m_second
self._m_second = (self.first_and_second % 40)
return getattr(self, '_m_second', None)
class LenEncoded(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self.b1 = self._io.read_u1()
if self.b1 == 130:
self.int2 = self._io.read_u2be()
if self.b1 == 129:
self.int1 = self._io.read_u1()
@property
def result(self):
if hasattr(self, '_m_result'):
return self._m_result
self._m_result = (self.int1 if self.b1 == 129 else (self.int2 if self.b1 == 130 else self.b1))
return getattr(self, '_m_result', None)
class BodyPrintableString(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self.str = (self._io.read_bytes_full()).decode(u"ASCII")