]> Cypherpunks.ru repositories - pyderasn.git/blobdiff - pyderasn.py
Convenient decod() helper method
[pyderasn.git] / pyderasn.py
index eca1825efd03429bcb88c3d7ef265644339565b9..5f0c0343ccd0d4153d29e6328fde4a73882229ec 100755 (executable)
@@ -1,12 +1,11 @@
 #!/usr/bin/env python
 # coding: utf-8
 # PyDERASN -- Python ASN.1 DER/BER codec with abstract structures
-# Copyright (C) 2017-2018 Sergey Matveev <stargrave@stargrave.org>
+# Copyright (C) 2017-2020 Sergey Matveev <stargrave@stargrave.org>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Lesser General Public License as
-# published by the Free Software Foundation, either version 3 of the
-# License, or (at your option) any later version.
+# published by the Free Software Foundation, version 3 of the License.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ -14,8 +13,7 @@
 # GNU Lesser General Public License for more details.
 #
 # You should have received a copy of the GNU Lesser General Public
-# License along with this program.  If not, see
-# <http://www.gnu.org/licenses/>.
+# License along with this program.  If not, see <http://www.gnu.org/licenses/>.
 """Python ASN.1 DER/BER codec with abstract structures
 
 This library allows you to marshal various structures in ASN.1 DER
@@ -239,6 +237,105 @@ all object ``repr``. But it is easy to write custom formatters.
     >>> print(pprint(obj))
         0   [1,1,   2] INTEGER -12345
 
+.. _pprint_example:
+
+Example certificate::
+
+    >>> print(pprint(crt))
+        0   [1,3,1604] Certificate SEQUENCE
+        4   [1,3,1453]  . tbsCertificate: TBSCertificate SEQUENCE
+       10-2 [1,1,   1]  . . version: [0] EXPLICIT Version INTEGER v3 OPTIONAL
+       13   [1,1,   3]  . . serialNumber: CertificateSerialNumber INTEGER 61595
+       18   [1,1,  13]  . . signature: AlgorithmIdentifier SEQUENCE
+       20   [1,1,   9]  . . . algorithm: OBJECT IDENTIFIER 1.2.840.113549.1.1.5
+       31   [0,0,   2]  . . . parameters: [UNIV 5] ANY OPTIONAL
+                        . . . . 05:00
+       33   [0,0, 278]  . . issuer: Name CHOICE rdnSequence
+       33   [1,3, 274]  . . . rdnSequence: RDNSequence SEQUENCE OF
+       37   [1,1,  11]  . . . . 0: RelativeDistinguishedName SET OF
+       39   [1,1,   9]  . . . . . 0: AttributeTypeAndValue SEQUENCE
+       41   [1,1,   3]  . . . . . . type: AttributeType OBJECT IDENTIFIER 2.5.4.6
+       46   [0,0,   4]  . . . . . . value: [UNIV 19] AttributeValue ANY
+                        . . . . . . . 13:02:45:53
+    [...]
+     1461   [1,1,  13]  . signatureAlgorithm: AlgorithmIdentifier SEQUENCE
+     1463   [1,1,   9]  . . algorithm: OBJECT IDENTIFIER 1.2.840.113549.1.1.5
+     1474   [0,0,   2]  . . parameters: [UNIV 5] ANY OPTIONAL
+                        . . . 05:00
+     1476   [1,2, 129]  . signatureValue: BIT STRING 1024 bits
+                        . . 68:EE:79:97:97:DD:3B:EF:16:6A:06:F2:14:9A:6E:CD
+                        . . 9E:12:F7:AA:83:10:BD:D1:7C:98:FA:C7:AE:D4:0E:2C
+     [...]
+
+    Trailing data: 0a
+
+Let's parse that output, human::
+
+       10-2 [1,1,   1]    . . version: [0] EXPLICIT Version INTEGER v3 OPTIONAL
+       ^  ^  ^ ^    ^     ^   ^        ^            ^       ^       ^  ^
+       0  1  2 3    4     5   6        7            8       9       10 11
+
+::
+
+       20   [1,1,   9]    . . . algorithm: OBJECT IDENTIFIER 1.2.840.113549.1.1.5
+       ^     ^ ^    ^     ^     ^          ^                 ^
+       0     2 3    4     5     6          9                 10
+
+::
+
+       33   [0,0, 278]    . . issuer: Name CHOICE rdnSequence
+       ^     ^ ^    ^     ^   ^       ^    ^      ^
+       0     2 3    4     5   6       8    9      10
+
+::
+
+       52-2∞ B [1,1,1054]∞  . . . . eContent: [0] EXPLICIT BER OCTET STRING 1046 bytes
+             ^           ^                                 ^   ^            ^
+            12          13                                14   9            10
+
+:0:
+ Offset of the object, where its DER/BER encoding begins.
+ Pay attention that it does **not** include explicit tag.
+:1:
+ If explicit tag exists, then this is its length (tag + encoded length).
+:2:
+ Length of object's tag. For example CHOICE does not have its own tag,
+ so it is zero.
+:3:
+ Length of encoded length.
+:4:
+ Length of encoded value.
+:5:
+ Visual indentation to show the depth of object in the hierarchy.
+:6:
+ Object's name inside SEQUENCE/CHOICE.
+:7:
+ If either IMPLICIT or EXPLICIT tag is set, then it will be shown
+ here. "IMPLICIT" is omitted.
+:8:
+ Object's class name, if set. Omitted if it is just an ordinary simple
+ value (like with ``algorithm`` in example above).
+:9:
+ Object's ASN.1 type.
+:10:
+ Object's value, if set. Can consist of multiple words (like OCTET/BIT
+ STRINGs above). We see ``v3`` value in Version, because it is named.
+ ``rdnSequence`` is the choice of CHOICE type.
+:11:
+ Possible other flags like OPTIONAL and DEFAULT, if value equals to the
+ default one, specified in the schema.
+:12:
+ Shows does object contains any kind of BER encoded data (possibly
+ Sequence holding BER-encoded underlying value).
+:13:
+ Only applicable to BER encoded data. Indefinite length encoding mark.
+:14:
+ Only applicable to BER encoded data. If object has BER-specific
+ encoding, then ``BER`` will be shown. It does not depend on indefinite
+ length encoding. ``EOC``, ``BOOLEAN``, ``BIT STRING``, ``OCTET STRING``
+ (and its derivatives), ``SET``, ``SET OF`` could be BERed.
+
+
 .. _definedby:
 
 DEFINED BY
@@ -249,6 +346,8 @@ DEFINED BY some previously met ObjectIdentifier. This library provides
 ability to specify mapping between some OID and field that must be
 decoded with specific specification.
 
+.. _defines:
+
 defines kwarg
 _____________
 
@@ -322,15 +421,15 @@ value must be sequence of following tuples::
 
 where ``decode_path`` is a tuple holding so-called decode path to the
 exact :py:class:`pyderasn.ObjectIdentifier` field you want to apply
-``defines``, holding exactly the same value as accepted in its keyword
-argument.
+``defines``, holding exactly the same value as accepted in its
+:ref:`keyword argument <defines>`.
 
 For example, again for CMS, you want to automatically decode
 ``SignedData`` and CMC's (:rfc:`5272`) ``PKIData`` and ``PKIResponse``
 structures it may hold. Also, automatically decode ``controlSequence``
 of ``PKIResponse``::
 
-    content_info, tail = ContentInfo().decode(data, defines_by_path=(
+    content_info, tail = ContentInfo().decode(data, ctx={"defines_by_path": (
         (
             ("contentType",),
             ((("content",), {id_signedData: SignedData()}),),
@@ -365,7 +464,7 @@ of ``PKIResponse``::
                 id_cmc_transactionId: TransactionId(),
             })),
         ),
-    ))
+    )})
 
 Pay attention for :py:class:`pyderasn.DecodePathDefBy` and ``any``.
 First function is useful for path construction when some automatic
@@ -384,7 +483,8 @@ constructed primitive types should be parsed successfully.
 
 * If object is encoded in BER form (not the DER one), then ``ber_encoded``
   attribute is set to True. Only ``BOOLEAN``, ``BIT STRING``, ``OCTET
-  STRING``, ``SEQUENCE``, ``SET``, ``SET OF`` can contain it.
+  STRING``, ``OBJECT IDENTIFIER``, ``SEQUENCE``, ``SET``, ``SET OF``
+  can contain it.
 * If object has an indefinite length encoding, then its ``lenindef``
   attribute is set to True. Only ``BIT STRING``, ``OCTET STRING``,
   ``SEQUENCE``, ``SET``, ``SEQUENCE OF``, ``SET OF``, ``ANY`` can
@@ -417,6 +517,11 @@ lengths will be invalid in that case.
    This option should be used only for skipping some decode errors, just
    to see the decoded structure somehow.
 
+Base Obj
+--------
+.. autoclass:: pyderasn.Obj
+   :members:
+
 Primitive types
 ---------------
 
@@ -462,6 +567,10 @@ NumericString
 _____________
 .. autoclass:: pyderasn.NumericString
 
+PrintableString
+_______________
+.. autoclass:: pyderasn.PrintableString
+
 UTCTime
 _______
 .. autoclass:: pyderasn.UTCTime
@@ -515,16 +624,17 @@ Various
 -------
 
 .. autofunction:: pyderasn.abs_decode_path
+.. autofunction:: pyderasn.colonize_hex
 .. autofunction:: pyderasn.hexenc
 .. autofunction:: pyderasn.hexdec
 .. autofunction:: pyderasn.tag_encode
 .. autofunction:: pyderasn.tag_decode
 .. autofunction:: pyderasn.tag_ctxp
 .. autofunction:: pyderasn.tag_ctxc
-.. autoclass:: pyderasn.Obj
 .. autoclass:: pyderasn.DecodeError
    :members: __init__
 .. autoclass:: pyderasn.NotEnoughData
+.. autoclass:: pyderasn.ExceedingData
 .. autoclass:: pyderasn.LenIndefForm
 .. autoclass:: pyderasn.TagMismatch
 .. autoclass:: pyderasn.InvalidLength
@@ -539,9 +649,11 @@ from codecs import getdecoder
 from codecs import getencoder
 from collections import namedtuple
 from collections import OrderedDict
+from copy import copy
 from datetime import datetime
 from math import ceil
 from os import environ
+from string import ascii_letters
 from string import digits
 
 from six import add_metaclass
@@ -551,18 +663,22 @@ from six import indexbytes
 from six import int2byte
 from six import integer_types
 from six import iterbytes
+from six import iteritems
+from six import itervalues
 from six import PY2
 from six import string_types
 from six import text_type
+from six import unichr as six_unichr
 from six.moves import xrange as six_xrange
 
 
 try:
     from termcolor import colored
-except ImportError:
-    def colored(what, *args):
+except ImportError:  # pragma: no cover
+    def colored(what, *args, **kwargs):
         return what
 
+__version__ = "5.6"
 
 __all__ = (
     "Any",
@@ -574,6 +690,7 @@ __all__ = (
     "DecodeError",
     "DecodePathDefBy",
     "Enumerated",
+    "ExceedingData",
     "GeneralizedTime",
     "GeneralString",
     "GraphicString",
@@ -641,7 +758,11 @@ LENINDEF_PP_CHAR = "I" if PY2 else "∞"
 # Errors
 ########################################################################
 
-class DecodeError(Exception):
+class ASN1Error(ValueError):
+    pass
+
+
+class DecodeError(ASN1Error):
     def __init__(self, msg="", klass=None, decode_path=(), offset=0):
         """
         :param str msg: reason of decode failing
@@ -680,6 +801,18 @@ class NotEnoughData(DecodeError):
     pass
 
 
+class ExceedingData(ASN1Error):
+    def __init__(self, nbytes):
+        super(ExceedingData, self).__init__()
+        self.nbytes = nbytes
+
+    def __str__(self):
+        return "%d trailing bytes" % self.nbytes
+
+    def __repr__(self):
+        return "%s(%s)" % (self.__class__.__name__, self)
+
+
 class LenIndefForm(DecodeError):
     pass
 
@@ -696,7 +829,7 @@ class InvalidOID(DecodeError):
     pass
 
 
-class ObjUnknown(ValueError):
+class ObjUnknown(ASN1Error):
     def __init__(self, name):
         super(ObjUnknown, self).__init__()
         self.name = name
@@ -708,7 +841,7 @@ class ObjUnknown(ValueError):
         return "%s(%s)" % (self.__class__.__name__, self)
 
 
-class ObjNotReady(ValueError):
+class ObjNotReady(ASN1Error):
     def __init__(self, name):
         super(ObjNotReady, self).__init__()
         self.name = name
@@ -720,7 +853,7 @@ class ObjNotReady(ValueError):
         return "%s(%s)" % (self.__class__.__name__, self)
 
 
-class InvalidValueType(ValueError):
+class InvalidValueType(ASN1Error):
     def __init__(self, expected_types):
         super(InvalidValueType, self).__init__()
         self.expected_types = expected_types
@@ -734,7 +867,7 @@ class InvalidValueType(ValueError):
         return "%s(%s)" % (self.__class__.__name__, self)
 
 
-class BoundsError(ValueError):
+class BoundsError(ASN1Error):
     def __init__(self, bound_min, value, bound_max):
         super(BoundsError, self).__init__()
         self.bound_min = bound_min
@@ -905,9 +1038,9 @@ def len_decode(data):
 ########################################################################
 
 class AutoAddSlots(type):
-    def __new__(mcs, name, bases, _dict):
+    def __new__(cls, name, bases, _dict):
         _dict["__slots__"] = _dict.get("__slots__", ())
-        return type.__new__(mcs, name, bases, _dict)
+        return type.__new__(cls, name, bases, _dict)
 
 
 @add_metaclass(AutoAddSlots)
@@ -981,10 +1114,14 @@ class Obj(object):
 
     @property
     def tlen(self):
+        """See :ref:`decoding`
+        """
         return len(self.tag)
 
     @property
     def tlvlen(self):
+        """See :ref:`decoding`
+        """
         return self.tlen + self.llen + self.vlen
 
     def __str__(self):  # pragma: no cover
@@ -1009,6 +1146,10 @@ class Obj(object):
         raise NotImplementedError()
 
     def encode(self):
+        """Encode the structure
+
+        :returns: DER representation
+        """
         raw = self._encode()
         if self._expl is None:
             return raw
@@ -1022,6 +1163,7 @@ class Obj(object):
             decode_path=(),
             ctx=None,
             tag_only=False,
+            _ctx_immutable=True,
     ):
         """Decode the data
 
@@ -1029,14 +1171,19 @@ class Obj(object):
         :param int offset: initial data's offset
         :param bool leavemm: do we need to leave memoryview of remaining
                     data as is, or convert it to bytes otherwise
-        :param ctx: optional :ref:`context <ctx>` governing decoding process.
+        :param ctx: optional :ref:`context <ctx>` governing decoding process
         :param tag_only: decode only the tag, without length and contents
                          (used only in Choice and Set structures, trying to
                          determine if tag satisfies the scheme)
+        :param _ctx_immutable: do we need to copy ``ctx`` before using it
         :returns: (Obj, remaining data)
+
+        .. seealso:: :ref:`decoding`
         """
         if ctx is None:
             ctx = {}
+        elif _ctx_immutable:
+            ctx = copy(ctx)
         tlv = memoryview(data)
         if self._expl is None:
             result = self._decode(
@@ -1047,7 +1194,7 @@ class Obj(object):
                 tag_only=tag_only,
             )
             if tag_only:
-                return
+                return None
             obj, tail = result
         else:
             try:
@@ -1084,8 +1231,8 @@ class Obj(object):
                     ctx=ctx,
                     tag_only=tag_only,
                 )
-                if tag_only:
-                    return
+                if tag_only:  # pragma: no cover
+                    return None
                 obj, tail = result
                 eoc_expected, tail = tail[:EOC_LEN], tail[EOC_LEN:]
                 if eoc_expected.tobytes() != EOC:
@@ -1119,8 +1266,8 @@ class Obj(object):
                     ctx=ctx,
                     tag_only=tag_only,
                 )
-                if tag_only:
-                    return
+                if tag_only:  # pragma: no cover
+                    return None
                 obj, tail = result
                 if obj.tlvlen < l and not ctx.get("allow_expl_oob", False):
                     raise DecodeError(
@@ -1131,46 +1278,87 @@ class Obj(object):
                     )
         return obj, (tail if leavemm else tail.tobytes())
 
+    def decod(self, data, offset=0, decode_path=(), ctx=None):
+        """Decode the data, check that tail is empty
+
+        :raises ExceedingData: if tail is not empty
+
+        This is just a wrapper over :py:meth:`pyderasn.Obj.decode`
+        (decode without tail) that also checks that there is no
+        trailing data left.
+        """
+        obj, tail = self.decode(
+            data,
+            offset=offset,
+            decode_path=decode_path,
+            ctx=ctx,
+            leavemm=True,
+        )
+        if len(tail) > 0:
+            raise ExceedingData(len(tail))
+        return obj
+
     @property
     def expled(self):
+        """See :ref:`decoding`
+        """
         return self._expl is not None
 
     @property
     def expl_tag(self):
+        """See :ref:`decoding`
+        """
         return self._expl
 
     @property
     def expl_tlen(self):
+        """See :ref:`decoding`
+        """
         return len(self._expl)
 
     @property
     def expl_llen(self):
+        """See :ref:`decoding`
+        """
         if self.expl_lenindef:
             return 1
         return len(len_encode(self.tlvlen))
 
     @property
     def expl_offset(self):
+        """See :ref:`decoding`
+        """
         return self.offset - self.expl_tlen - self.expl_llen
 
     @property
     def expl_vlen(self):
+        """See :ref:`decoding`
+        """
         return self.tlvlen
 
     @property
     def expl_tlvlen(self):
+        """See :ref:`decoding`
+        """
         return self.expl_tlen + self.expl_llen + self.expl_vlen
 
     @property
     def fulloffset(self):
+        """See :ref:`decoding`
+        """
         return self.expl_offset if self.expled else self.offset
 
     @property
     def fulllen(self):
+        """See :ref:`decoding`
+        """
         return self.expl_tlvlen if self.expled else self.tlvlen
 
     def pps_lenindef(self, decode_path):
-        if self.lenindef:
+        if self.lenindef and not (
+            getattr(self, "defined", None) is not None and
+            self.defined[1].lenindef
+        ):
             yield _pp(
                 asn1_type_name="EOC",
                 obj_name="",
@@ -1227,6 +1415,7 @@ class DecodePathDefBy(object):
 ########################################################################
 
 PP = namedtuple("PP", (
+    "obj",
     "asn1_type_name",
     "obj_name",
     "decode_path",
@@ -1252,6 +1441,7 @@ PP = namedtuple("PP", (
 
 
 def _pp(
+        obj=None,
         asn1_type_name="unknown",
         obj_name="unknown",
         decode_path=(),
@@ -1275,6 +1465,7 @@ def _pp(
         bered=False,
 ):
     return PP(
+        obj,
         asn1_type_name,
         obj_name,
         decode_path,
@@ -1303,9 +1494,15 @@ def _colourize(what, colour, with_colours, attrs=("bold",)):
     return colored(what, colour, attrs=attrs) if with_colours else what
 
 
+def colonize_hex(hexed):
+    """Separate hexadecimal string with colons
+    """
+    return ":".join(hexed[i:i + 2] for i in six_xrange(0, len(hexed), 2))
+
+
 def pp_console_row(
         pp,
-        oids=None,
+        oid_maps=(),
         with_offsets=False,
         with_blob=True,
         with_colours=False,
@@ -1340,14 +1537,18 @@ def pp_console_row(
         if isinstance(ent, DecodePathDefBy):
             cols.append(_colourize("DEFINED BY", "red", with_colours, ("reverse",)))
             value = str(ent.defined_by)
+            oid_name = None
             if (
-                    oids is not None and
+                    len(oid_maps) > 0 and
                     ent.defined_by.asn1_type_name ==
-                    ObjectIdentifier.asn1_type_name and
-                    value in oids
+                    ObjectIdentifier.asn1_type_name
             ):
-                cols.append(_colourize("%s:" % oids[value], "green", with_colours))
-            else:
+                for oid_map in oid_maps:
+                    oid_name = oid_map.get(value)
+                    if oid_name is not None:
+                        cols.append(_colourize("%s:" % oid_name, "green", with_colours))
+                        break
+            if oid_name is None:
                 cols.append(_colourize("%s:" % value, "white", with_colours, ("reverse",)))
         else:
             cols.append(_colourize("%s:" % ent, "yellow", with_colours, ("reverse",)))
@@ -1368,11 +1569,23 @@ def pp_console_row(
         value = pp.value
         cols.append(_colourize(value, "white", with_colours, ("reverse",)))
         if (
-                oids is not None and
-                pp.asn1_type_name == ObjectIdentifier.asn1_type_name and
-                value in oids
+                len(oid_maps) > 0 and
+                pp.asn1_type_name == ObjectIdentifier.asn1_type_name
         ):
-            cols.append(_colourize("(%s)" % oids[value], "green", with_colours))
+            for oid_map in oid_maps:
+                oid_name = oid_map.get(value)
+                if oid_name is not None:
+                    cols.append(_colourize("(%s)" % oid_name, "green", with_colours))
+                    break
+        if pp.asn1_type_name == Integer.asn1_type_name:
+            hex_repr = hex(int(pp.obj._value))[2:].upper()
+            if len(hex_repr) % 2 != 0:
+                hex_repr = "0" + hex_repr
+            cols.append(_colourize(
+                "(%s)" % colonize_hex(hex_repr),
+                "green",
+                with_colours,
+            ))
     if with_blob:
         if isinstance(pp.blob, binary_type):
             cols.append(hexenc(pp.blob))
@@ -1398,18 +1611,16 @@ def pp_console_blob(pp, decode_path_len_decrease=0):
         cols.append(" ." * (decode_path_len + 1))
     if isinstance(pp.blob, binary_type):
         blob = hexenc(pp.blob).upper()
-        for i in range(0, len(blob), 32):
+        for i in six_xrange(0, len(blob), 32):
             chunk = blob[i:i + 32]
-            yield " ".join(cols + [":".join(
-                chunk[j:j + 2] for j in range(0, len(chunk), 2)
-            )])
+            yield " ".join(cols + [colonize_hex(chunk)])
     elif isinstance(pp.blob, tuple):
         yield " ".join(cols + [", ".join(pp.blob)])
 
 
 def pprint(
         obj,
-        oids=None,
+        oid_maps=(),
         big_blobs=False,
         with_colours=False,
         with_decode_path=False,
@@ -1418,8 +1629,9 @@ def pprint(
     """Pretty print object
 
     :param Obj obj: object you want to pretty print
-    :param oids: ``OID <-> humand readable string`` dictionary. When OID
-                 from it is met, then its humand readable form is printed
+    :param oid_maps: list of ``OID <-> humand readable string`` dictionary.
+                     When OID from it is met, then its humand readable form
+                     is printed
     :param big_blobs: if large binary objects are met (like OctetString
                       values), do we need to print them too, on separate
                       lines
@@ -1441,7 +1653,7 @@ def pprint(
                 if big_blobs:
                     yield pp_console_row(
                         pp,
-                        oids=oids,
+                        oid_maps=oid_maps,
                         with_offsets=True,
                         with_blob=False,
                         with_colours=with_colours,
@@ -1456,7 +1668,7 @@ def pprint(
                 else:
                     yield pp_console_row(
                         pp,
-                        oids=oids,
+                        oid_maps=oid_maps,
                         with_offsets=True,
                         with_blob=True,
                         with_colours=with_colours,
@@ -1517,10 +1729,10 @@ class Boolean(Obj):
                 self._value = default
 
     def _value_sanitize(self, value):
-        if issubclass(value.__class__, Boolean):
-            return value._value
         if isinstance(value, bool):
             return value
+        if issubclass(value.__class__, Boolean):
+            return value._value
         raise InvalidValueType((self.__class__, bool))
 
     @property
@@ -1537,6 +1749,9 @@ class Boolean(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         return obj
 
     def __nonzero__(self):
@@ -1599,7 +1814,7 @@ class Boolean(Obj):
                 offset=offset,
             )
         if tag_only:
-            return
+            return None
         try:
             l, _, v = len_decode(lv)
         except DecodeError as err:
@@ -1655,6 +1870,7 @@ class Boolean(Obj):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -1762,10 +1978,10 @@ class Integer(Obj):
                 self._value = default
 
     def _value_sanitize(self, value):
-        if issubclass(value.__class__, Integer):
-            value = value._value
-        elif isinstance(value, integer_types):
+        if isinstance(value, integer_types):
             pass
+        elif issubclass(value.__class__, Integer):
+            value = value._value
         elif isinstance(value, str):
             value = self.specs.get(value)
             if value is None:
@@ -1792,6 +2008,9 @@ class Integer(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         return obj
 
     def __int__(self):
@@ -1822,9 +2041,10 @@ class Integer(Obj):
 
     @property
     def named(self):
-        for name, value in self.specs.items():
+        for name, value in iteritems(self.specs):
             if value == self._value:
                 return name
+        return None
 
     def __call__(
             self,
@@ -1904,7 +2124,7 @@ class Integer(Obj):
                 offset=offset,
             )
         if tag_only:
-            return
+            return None
         try:
             l, llen, v = len_decode(lv)
         except DecodeError as err:
@@ -1982,6 +2202,7 @@ class Integer(Obj):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -2005,6 +2226,9 @@ class Integer(Obj):
             yield pp
 
 
+SET01 = frozenset(("0", "1"))
+
+
 class BitString(Obj):
     """``BIT STRING`` bit string type
 
@@ -2110,8 +2334,6 @@ class BitString(Obj):
         return bit_len, bytes(octets)
 
     def _value_sanitize(self, value):
-        if issubclass(value.__class__, BitString):
-            return value._value
         if isinstance(value, (string_types, binary_type)):
             if (
                     isinstance(value, string_types) and
@@ -2119,10 +2341,10 @@ class BitString(Obj):
             ):
                 if value.endswith("'B"):
                     value = value[1:-2]
-                    if not set(value) <= set(("0", "1")):
+                    if not frozenset(value) <= SET01:
                         raise ValueError("B's coding contains unacceptable chars")
                     return self._bits2octets(value)
-                elif value.endswith("'H"):
+                if value.endswith("'H"):
                     value = value[1:-2]
                     return (
                         len(value) * 4,
@@ -2130,8 +2352,7 @@ class BitString(Obj):
                     )
             if isinstance(value, binary_type):
                 return (len(value) * 8, value)
-            else:
-                raise InvalidValueType((self.__class__, string_types, binary_type))
+            raise InvalidValueType((self.__class__, string_types, binary_type))
         if isinstance(value, tuple):
             if (
                     len(value) == 2 and
@@ -2147,11 +2368,13 @@ class BitString(Obj):
                 bits.append(bit)
             if len(bits) == 0:
                 return self._bits2octets("")
-            bits = set(bits)
+            bits = frozenset(bits)
             return self._bits2octets("".join(
                 ("1" if bit in bits else "0")
                 for bit in six_xrange(max(bits) + 1)
             ))
+        if issubclass(value.__class__, BitString):
+            return value._value
         raise InvalidValueType((self.__class__, binary_type, string_types))
 
     @property
@@ -2171,6 +2394,9 @@ class BitString(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         return obj
 
     def __iter__(self):
@@ -2200,7 +2426,7 @@ class BitString(Obj):
 
     @property
     def named(self):
-        return [name for name, bit in self.specs.items() if self[bit]]
+        return [name for name, bit in iteritems(self.specs) if self[bit]]
 
     def __call__(
             self,
@@ -2245,7 +2471,7 @@ class BitString(Obj):
             octets,
         ))
 
-    def _decode_chunk(self, lv, offset, decode_path, ctx):
+    def _decode_chunk(self, lv, offset, decode_path):
         try:
             l, llen, v = len_decode(lv)
         except DecodeError as err:
@@ -2314,9 +2540,9 @@ class BitString(Obj):
                 offset=offset,
             )
         if t == self.tag:
-            if tag_only:
-                return
-            return self._decode_chunk(lv, offset, decode_path, ctx)
+            if tag_only:  # pragma: no cover
+                return None
+            return self._decode_chunk(lv, offset, decode_path)
         if t == self.tag_constructed:
             if not ctx.get("bered", False):
                 raise DecodeError(
@@ -2325,8 +2551,8 @@ class BitString(Obj):
                     decode_path=decode_path,
                     offset=offset,
                 )
-            if tag_only:
-                return
+            if tag_only:  # pragma: no cover
+                return None
             lenindef = False
             try:
                 l, llen, v = len_decode(lv)
@@ -2379,6 +2605,7 @@ class BitString(Obj):
                         decode_path=sub_decode_path,
                         leavemm=True,
                         ctx=ctx,
+                        _ctx_immutable=False,
                     )
                 except TagMismatch:
                     raise DecodeError(
@@ -2443,6 +2670,7 @@ class BitString(Obj):
             if len(self.specs) > 0:
                 blob = tuple(self.named)
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -2555,10 +2783,10 @@ class OctetString(Obj):
         )
 
     def _value_sanitize(self, value):
-        if issubclass(value.__class__, OctetString):
-            value = value._value
-        elif isinstance(value, binary_type):
+        if isinstance(value, binary_type):
             pass
+        elif issubclass(value.__class__, OctetString):
+            value = value._value
         else:
             raise InvalidValueType((self.__class__, bytes))
         if not self._bound_min <= len(value) <= self._bound_max:
@@ -2581,6 +2809,9 @@ class OctetString(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         return obj
 
     def __bytes__(self):
@@ -2630,7 +2861,7 @@ class OctetString(Obj):
             self._value,
         ))
 
-    def _decode_chunk(self, lv, offset, decode_path, ctx):
+    def _decode_chunk(self, lv, offset, decode_path):
         try:
             l, llen, v = len_decode(lv)
         except DecodeError as err:
@@ -2686,8 +2917,8 @@ class OctetString(Obj):
             )
         if t == self.tag:
             if tag_only:
-                return
-            return self._decode_chunk(lv, offset, decode_path, ctx)
+                return None
+            return self._decode_chunk(lv, offset, decode_path)
         if t == self.tag_constructed:
             if not ctx.get("bered", False):
                 raise DecodeError(
@@ -2697,7 +2928,7 @@ class OctetString(Obj):
                     offset=offset,
                 )
             if tag_only:
-                return
+                return None
             lenindef = False
             try:
                 l, llen, v = len_decode(lv)
@@ -2743,6 +2974,7 @@ class OctetString(Obj):
                         decode_path=sub_decode_path,
                         leavemm=True,
                         ctx=ctx,
+                        _ctx_immutable=False,
                     )
                 except TagMismatch:
                     raise DecodeError(
@@ -2793,6 +3025,7 @@ class OctetString(Obj):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -2865,6 +3098,9 @@ class Null(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         return obj
 
     def __eq__(self, their):
@@ -2907,8 +3143,8 @@ class Null(Obj):
                 decode_path=decode_path,
                 offset=offset,
             )
-        if tag_only:
-            return
+        if tag_only:  # pragma: no cover
+            return None
         try:
             l, _, v = len_decode(lv)
         except DecodeError as err:
@@ -2938,6 +3174,7 @@ class Null(Obj):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -3074,6 +3311,9 @@ class ObjectIdentifier(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         return obj
 
     def __iter__(self):
@@ -3158,8 +3398,8 @@ class ObjectIdentifier(Obj):
                 decode_path=decode_path,
                 offset=offset,
             )
-        if tag_only:
-            return
+        if tag_only:  # pragma: no cover
+            return None
         try:
             l, llen, v = len_decode(lv)
         except DecodeError as err:
@@ -3185,11 +3425,17 @@ class ObjectIdentifier(Obj):
             )
         v, tail = v[:l], v[l:]
         arcs = []
+        ber_encoded = False
         while len(v) > 0:
             i = 0
             arc = 0
             while True:
                 octet = indexbytes(v, i)
+                if i == 0 and octet == 0x80:
+                    if ctx.get("bered", False):
+                        ber_encoded = True
+                    else:
+                        raise DecodeError("non normalized arc encoding")
                 arc = (arc << 7) | (octet & 0x7F)
                 if octet & 0x80 == 0:
                     arcs.append(arc)
@@ -3221,6 +3467,8 @@ class ObjectIdentifier(Obj):
             optional=self.optional,
             _decoded=(offset, llen, l),
         )
+        if ber_encoded:
+            obj.ber_encoded = True
         return obj, tail
 
     def __repr__(self):
@@ -3228,6 +3476,7 @@ class ObjectIdentifier(Obj):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -3245,6 +3494,7 @@ class ObjectIdentifier(Obj):
             expl_llen=self.expl_llen if self.expled else None,
             expl_vlen=self.expl_vlen if self.expled else None,
             expl_lenindef=self.expl_lenindef,
+            ber_encoded=self.ber_encoded,
             bered=self.bered,
         )
         for pp in self.pps_lenindef(decode_path):
@@ -3288,7 +3538,10 @@ class Enumerated(Integer):
         if isinstance(value, self.__class__):
             value = value._value
         elif isinstance(value, integer_types):
-            if value not in list(self.specs.values()):
+            for _value in itervalues(self.specs):
+                if _value == value:
+                    break
+            else:
                 raise DecodeError(
                     "unknown integer value: %s" % value,
                     klass=self.__class__,
@@ -3313,6 +3566,9 @@ class Enumerated(Integer):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         return obj
 
     def __call__(
@@ -3454,6 +3710,7 @@ class CommonString(OctetString):
         if self.ready:
             value = hexenc(bytes(self)) if no_unicode else self.__unicode__()
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -3485,29 +3742,57 @@ class UTF8String(CommonString):
     asn1_type_name = "UTF8String"
 
 
-class NumericString(CommonString):
+class AllowableCharsMixin(object):
+    @property
+    def allowable_chars(self):
+        if PY2:
+            return self._allowable_chars
+        return frozenset(six_unichr(c) for c in self._allowable_chars)
+
+
+class NumericString(AllowableCharsMixin, CommonString):
     """Numeric string
 
-    Its value is properly sanitized: only ASCII digits can be stored.
+    Its value is properly sanitized: only ASCII digits with spaces can
+    be stored.
+
+    >>> NumericString().allowable_chars
+    frozenset(['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ' '])
     """
     __slots__ = ()
     tag_default = tag_encode(18)
     encoding = "ascii"
     asn1_type_name = "NumericString"
-    allowable_chars = set(digits.encode("ascii"))
+    _allowable_chars = frozenset(digits.encode("ascii") + b" ")
 
     def _value_sanitize(self, value):
         value = super(NumericString, self)._value_sanitize(value)
-        if not set(value) <= self.allowable_chars:
+        if not frozenset(value) <= self._allowable_chars:
             raise DecodeError("non-numeric value")
         return value
 
 
-class PrintableString(CommonString):
+class PrintableString(AllowableCharsMixin, CommonString):
+    """Printable string
+
+    Its value is properly sanitized: see X.680 41.4 table 10.
+
+    >>> PrintableString().allowable_chars
+    frozenset([' ', "'", ..., 'z'])
+    """
     __slots__ = ()
     tag_default = tag_encode(19)
     encoding = "ascii"
     asn1_type_name = "PrintableString"
+    _allowable_chars = frozenset(
+        (ascii_letters + digits + " '()+,-./:=?").encode("ascii")
+    )
+
+    def _value_sanitize(self, value):
+        value = super(PrintableString, self)._value_sanitize(value)
+        if not frozenset(value) <= self._allowable_chars:
+            raise DecodeError("non-printable value")
+        return value
 
 
 class TeletexString(CommonString):
@@ -3554,14 +3839,16 @@ class UTCTime(CommonString):
     datetime.datetime(2017, 9, 30, 22, 7, 50)
     >>> UTCTime(datetime(2057, 9, 30, 22, 7, 50)).todatetime()
     datetime.datetime(1957, 9, 30, 22, 7, 50)
+
+    .. warning::
+
+       BER encoding is unsupported.
     """
     __slots__ = ()
     tag_default = tag_encode(23)
     encoding = "ascii"
     asn1_type_name = "UTCTime"
 
-    fmt = "%y%m%d%H%M%SZ"
-
     def __init__(
             self,
             value=None,
@@ -3600,24 +3887,36 @@ class UTCTime(CommonString):
             if self._value is None:
                 self._value = default
 
+    def _strptime(self, value):
+        # datetime.strptime's format: %y%m%d%H%M%SZ
+        if len(value) != LEN_YYMMDDHHMMSSZ:
+            raise ValueError("invalid UTCTime length")
+        if value[-1] != "Z":
+            raise ValueError("non UTC timezone")
+        return datetime(
+            2000 + int(value[:2]),  # %y
+            int(value[2:4]),  # %m
+            int(value[4:6]),  # %d
+            int(value[6:8]),  # %H
+            int(value[8:10]),  # %M
+            int(value[10:12]),  # %S
+        )
+
     def _value_sanitize(self, value):
-        if isinstance(value, self.__class__):
-            return value._value
-        if isinstance(value, datetime):
-            return value.strftime(self.fmt).encode("ascii")
         if isinstance(value, binary_type):
             try:
                 value_decoded = value.decode("ascii")
             except (UnicodeEncodeError, UnicodeDecodeError) as err:
-                raise DecodeError("invalid UTCTime encoding")
-            if len(value_decoded) == LEN_YYMMDDHHMMSSZ:
-                try:
-                    datetime.strptime(value_decoded, self.fmt)
-                except (TypeError, ValueError):
-                    raise DecodeError("invalid UTCTime format")
-                return value
-            else:
-                raise DecodeError("invalid UTCTime length")
+                raise DecodeError("invalid UTCTime encoding: %r" % err)
+            try:
+                self._strptime(value_decoded)
+            except (TypeError, ValueError) as err:
+                raise DecodeError("invalid UTCTime format: %r" % err)
+            return value
+        if isinstance(value, self.__class__):
+            return value._value
+        if isinstance(value, datetime):
+            return value.strftime("%y%m%d%H%M%SZ").encode("ascii")
         raise InvalidValueType((self.__class__, datetime))
 
     def __eq__(self, their):
@@ -3642,7 +3941,7 @@ class UTCTime(CommonString):
         having < 50 years are treated as 20xx, 19xx otherwise, according
         to X.509 recomendation.
         """
-        value = datetime.strptime(self._value.decode("ascii"), self.fmt)
+        value = self._strptime(self._value.decode("ascii"))
         year = value.year % 100
         return datetime(
             year=(2000 + year) if year < 50 else (1900 + year),
@@ -3658,6 +3957,7 @@ class UTCTime(CommonString):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -3693,54 +3993,85 @@ class GeneralizedTime(UTCTime):
     '20170930220750.000123Z'
     >>> t = GeneralizedTime(datetime(2057, 9, 30, 22, 7, 50))
     GeneralizedTime GeneralizedTime 2057-09-30T22:07:50
+
+    .. warning::
+
+       BER encoding is unsupported.
+
+    .. warning::
+
+       Only microsecond fractions are supported.
+       :py:exc:`pyderasn.DecodeError` will be raised during decoding of
+       higher precision values.
     """
     __slots__ = ()
     tag_default = tag_encode(24)
     asn1_type_name = "GeneralizedTime"
 
-    fmt = "%Y%m%d%H%M%SZ"
-    fmt_ms = "%Y%m%d%H%M%S.%fZ"
+    def _strptime(self, value):
+        l = len(value)
+        if l == LEN_YYYYMMDDHHMMSSZ:
+            # datetime.strptime's format: %y%m%d%H%M%SZ
+            if value[-1] != "Z":
+                raise ValueError("non UTC timezone")
+            return datetime(
+                int(value[:4]),  # %Y
+                int(value[4:6]),  # %m
+                int(value[6:8]),  # %d
+                int(value[8:10]),  # %H
+                int(value[10:12]),  # %M
+                int(value[12:14]),  # %S
+            )
+        if l >= LEN_YYYYMMDDHHMMSSDMZ:
+            # datetime.strptime's format: %Y%m%d%H%M%S.%fZ
+            if value[-1] != "Z":
+                raise ValueError("non UTC timezone")
+            if value[14] != ".":
+                raise ValueError("no fractions separator")
+            us = value[15:-1]
+            if us[-1] == "0":
+                raise ValueError("trailing zero")
+            us_len = len(us)
+            if us_len > 6:
+                raise ValueError("only microsecond fractions are supported")
+            us = int(us + ("0" * (6 - us_len)))
+            decoded = datetime(
+                int(value[:4]),  # %Y
+                int(value[4:6]),  # %m
+                int(value[6:8]),  # %d
+                int(value[8:10]),  # %H
+                int(value[10:12]),  # %M
+                int(value[12:14]),  # %S
+                us,  # %f
+            )
+            return decoded
+        raise ValueError("invalid GeneralizedTime length")
 
     def _value_sanitize(self, value):
-        if isinstance(value, self.__class__):
-            return value._value
-        if isinstance(value, datetime):
-            return value.strftime(
-                self.fmt_ms if value.microsecond > 0 else self.fmt
-            ).encode("ascii")
         if isinstance(value, binary_type):
             try:
                 value_decoded = value.decode("ascii")
             except (UnicodeEncodeError, UnicodeDecodeError) as err:
-                raise DecodeError("invalid GeneralizedTime encoding")
-            if len(value_decoded) == LEN_YYYYMMDDHHMMSSZ:
-                try:
-                    datetime.strptime(value_decoded, self.fmt)
-                except (TypeError, ValueError):
-                    raise DecodeError(
-                        "invalid GeneralizedTime (without ms) format",
-                    )
-                return value
-            elif len(value_decoded) >= LEN_YYYYMMDDHHMMSSDMZ:
-                try:
-                    datetime.strptime(value_decoded, self.fmt_ms)
-                except (TypeError, ValueError):
-                    raise DecodeError(
-                        "invalid GeneralizedTime (with ms) format",
-                    )
-                return value
-            else:
+                raise DecodeError("invalid GeneralizedTime encoding: %r" % err)
+            try:
+                self._strptime(value_decoded)
+            except (TypeError, ValueError) as err:
                 raise DecodeError(
-                    "invalid GeneralizedTime length",
+                    "invalid GeneralizedTime format: %r" % err,
                     klass=self.__class__,
                 )
+            return value
+        if isinstance(value, self.__class__):
+            return value._value
+        if isinstance(value, datetime):
+            encoded = value.strftime("%Y%m%d%H%M%S")
+            if value.microsecond > 0:
+                encoded = encoded + (".%06d" % value.microsecond).rstrip("0")
+            return (encoded + "Z").encode("ascii")
         raise InvalidValueType((self.__class__, datetime))
 
     def todatetime(self):
-        value = self._value.decode("ascii")
-        if len(value) == LEN_YYYYMMDDHHMMSSZ:
-            return datetime.strptime(value, self.fmt)
-        return datetime.strptime(value, self.fmt_ms)
+        return self._strptime(self._value.decode("ascii"))
 
 
 class GraphicString(CommonString):
@@ -3859,8 +4190,6 @@ class Choice(Obj):
                 self._value = default_obj.copy()._value
 
     def _value_sanitize(self, value):
-        if isinstance(value, self.__class__):
-            return value._value
         if isinstance(value, tuple) and len(value) == 2:
             choice, obj = value
             spec = self.specs.get(choice)
@@ -3869,6 +4198,8 @@ class Choice(Obj):
             if not isinstance(obj, spec.__class__):
                 raise InvalidValueType((spec,))
             return (choice, spec(obj))
+        if isinstance(value, self.__class__):
+            return value._value
         raise InvalidValueType((self.__class__, tuple))
 
     @property
@@ -3890,6 +4221,9 @@ class Choice(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         value = self._value
         if value is not None:
             obj._value = (value[0], value[1].copy())
@@ -3961,7 +4295,7 @@ class Choice(Obj):
         return self._value[1].encode()
 
     def _decode(self, tlv, offset, decode_path, ctx, tag_only):
-        for choice, spec in self.specs.items():
+        for choice, spec in iteritems(self.specs):
             sub_decode_path = decode_path + (choice,)
             try:
                 spec.decode(
@@ -3971,6 +4305,7 @@ class Choice(Obj):
                     decode_path=sub_decode_path,
                     ctx=ctx,
                     tag_only=True,
+                    _ctx_immutable=False,
                 )
             except TagMismatch:
                 continue
@@ -3981,14 +4316,15 @@ class Choice(Obj):
                 decode_path=decode_path,
                 offset=offset,
             )
-        if tag_only:
-            return
+        if tag_only:  # pragma: no cover
+            return None
         value, tail = spec.decode(
             tlv,
             offset=offset,
             leavemm=True,
             decode_path=sub_decode_path,
             ctx=ctx,
+            _ctx_immutable=False,
         )
         obj = self.__class__(
             schema=self.specs,
@@ -4008,6 +4344,7 @@ class Choice(Obj):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -4098,12 +4435,12 @@ class Any(Obj):
         self.defined = None
 
     def _value_sanitize(self, value):
+        if isinstance(value, binary_type):
+            return value
         if isinstance(value, self.__class__):
             return value._value
         if isinstance(value, Obj):
             return value.encode()
-        if isinstance(value, binary_type):
-            return value
         raise InvalidValueType((self.__class__, Obj, binary_type))
 
     @property
@@ -4127,6 +4464,9 @@ class Any(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         return obj
 
     def __eq__(self, their):
@@ -4190,6 +4530,7 @@ class Any(Obj):
                     decode_path=decode_path + (str(chunk_i),),
                     leavemm=True,
                     ctx=ctx,
+                    _ctx_immutable=False,
                 )
                 vlen += chunk.tlvlen
                 sub_offset += chunk.tlvlen
@@ -4234,6 +4575,7 @@ class Any(Obj):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -4283,8 +4625,7 @@ def get_def_by_path(defines_by_path, sub_decode_path):
 def abs_decode_path(decode_path, rel_path):
     """Create an absolute decode path from current and relative ones
 
-    :param decode_path: current decode path, starting point.
-                        Tuple of strings
+    :param decode_path: current decode path, starting point. Tuple of strings
     :param rel_path: relative path to ``decode_path``. Tuple of strings.
                      If first tuple's element is "/", then treat it as
                      an absolute path, ignoring ``decode_path`` as
@@ -4439,22 +4780,21 @@ class Sequence(Obj):
 
     @property
     def ready(self):
-        for name, spec in self.specs.items():
+        for name, spec in iteritems(self.specs):
             value = self._value.get(name)
             if value is None:
                 if spec.optional:
                     continue
                 return False
-            else:
-                if not value.ready:
-                    return False
+            if not value.ready:
+                return False
         return True
 
     @property
     def bered(self):
         if self.expl_lenindef or self.lenindef or self.ber_encoded:
             return True
-        return any(value.bered for value in self._value.values())
+        return any(value.bered for value in itervalues(self._value))
 
     def copy(self):
         obj = self.__class__(schema=self.specs)
@@ -4465,7 +4805,10 @@ class Sequence(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
-        obj._value = {k: v.copy() for k, v in self._value.items()}
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
+        obj._value = {k: v.copy() for k, v in iteritems(self._value)}
         return obj
 
     def __eq__(self, their):
@@ -4526,7 +4869,7 @@ class Sequence(Obj):
 
     def _encoded_values(self):
         raws = []
-        for name, spec in self.specs.items():
+        for name, spec in iteritems(self.specs):
             value = self._value.get(name)
             if value is None:
                 if spec.optional:
@@ -4555,8 +4898,8 @@ class Sequence(Obj):
                 decode_path=decode_path,
                 offset=offset,
             )
-        if tag_only:
-            return
+        if tag_only:  # pragma: no cover
+            return None
         lenindef = False
         ctx_bered = ctx.get("bered", False)
         try:
@@ -4592,7 +4935,7 @@ class Sequence(Obj):
         values = {}
         ber_encoded = False
         ctx_allow_default_values = ctx.get("allow_default_values", False)
-        for name, spec in self.specs.items():
+        for name, spec in iteritems(self.specs):
             if spec.optional and (
                     (lenindef and v[:EOC_LEN].tobytes() == EOC) or
                     len(v) == 0
@@ -4606,9 +4949,10 @@ class Sequence(Obj):
                     leavemm=True,
                     decode_path=sub_decode_path,
                     ctx=ctx,
+                    _ctx_immutable=False,
                 )
-            except TagMismatch:
-                if spec.optional:
+            except TagMismatch as err:
+                if (len(err.decode_path) == len(decode_path) + 1) and spec.optional:
                     continue
                 raise
 
@@ -4630,6 +4974,7 @@ class Sequence(Obj):
                             leavemm=True,
                             decode_path=sub_sub_decode_path,
                             ctx=ctx,
+                            _ctx_immutable=False,
                         )
                         if len(defined_tail) > 0:
                             raise DecodeError(
@@ -4649,6 +4994,7 @@ class Sequence(Obj):
                         leavemm=True,
                         decode_path=sub_decode_path + (DecodePathDefBy(defined_by),),
                         ctx=ctx,
+                        _ctx_immutable=False,
                     )
                     if len(defined_tail) > 0:
                         raise DecodeError(
@@ -4730,6 +5076,7 @@ class Sequence(Obj):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -4782,6 +5129,9 @@ class Set(Sequence):
         v = b"".join(raws)
         return b"".join((self.tag, len_encode(len(v)), v))
 
+    def _specs_items(self):
+        return iteritems(self.specs)
+
     def _decode(self, tlv, offset, decode_path, ctx, tag_only):
         try:
             t, tlen, lv = tag_strip(tlv)
@@ -4799,7 +5149,7 @@ class Set(Sequence):
                 offset=offset,
             )
         if tag_only:
-            return
+            return None
         lenindef = False
         ctx_bered = ctx.get("bered", False)
         try:
@@ -4836,11 +5186,11 @@ class Set(Sequence):
         ctx_allow_default_values = ctx.get("allow_default_values", False)
         ctx_allow_unordered_set = ctx.get("allow_unordered_set", False)
         value_prev = memoryview(v[:0])
-        specs_items = self.specs.items
+
         while len(v) > 0:
             if lenindef and v[:EOC_LEN].tobytes() == EOC:
                 break
-            for name, spec in specs_items():
+            for name, spec in self._specs_items():
                 sub_decode_path = decode_path + (name,)
                 try:
                     spec.decode(
@@ -4850,6 +5200,7 @@ class Set(Sequence):
                         decode_path=sub_decode_path,
                         ctx=ctx,
                         tag_only=True,
+                        _ctx_immutable=False,
                     )
                 except TagMismatch:
                     continue
@@ -4866,6 +5217,7 @@ class Set(Sequence):
                 leavemm=True,
                 decode_path=sub_decode_path,
                 ctx=ctx,
+                _ctx_immutable=False,
             )
             value_len = value.fulllen
             if value_prev.tobytes() > v[:value_len].tobytes():
@@ -5036,6 +5388,9 @@ class SequenceOf(Obj):
         obj.offset = self.offset
         obj.llen = self.llen
         obj.vlen = self.vlen
+        obj.expl_lenindef = self.expl_lenindef
+        obj.lenindef = self.lenindef
+        obj.ber_encoded = self.ber_encoded
         obj._value = [v.copy() for v in self._value]
         return obj
 
@@ -5127,7 +5482,7 @@ class SequenceOf(Obj):
                 offset=offset,
             )
         if tag_only:
-            return
+            return None
         lenindef = False
         ctx_bered = ctx.get("bered", False)
         try:
@@ -5175,6 +5530,7 @@ class SequenceOf(Obj):
                 leavemm=True,
                 decode_path=sub_decode_path,
                 ctx=ctx,
+                _ctx_immutable=False,
             )
             value_len = value.fulllen
             if ordering_check:
@@ -5232,6 +5588,7 @@ class SequenceOf(Obj):
 
     def pps(self, decode_path=()):
         yield _pp(
+            obj=self,
             asn1_type_name=self.asn1_type_name,
             obj_name=self.__class__.__name__,
             decode_path=decode_path,
@@ -5307,7 +5664,7 @@ def generic_decoder():  # pragma: no cover
     choice = PrimitiveTypes()
     choice.specs["SequenceOf"] = SequenceOf(schema=choice)
     choice.specs["SetOf"] = SetOf(schema=choice)
-    for i in range(31):
+    for i in six_xrange(31):
         choice.specs["SequenceOf%d" % i] = SequenceOf(
             schema=choice,
             expl=tag_ctxc(i),
@@ -5321,7 +5678,7 @@ def generic_decoder():  # pragma: no cover
 
     def pprint_any(
             obj,
-            oids=None,
+            oid_maps=(),
             with_colours=False,
             with_decode_path=False,
             decode_path_only=(),
@@ -5341,7 +5698,7 @@ def generic_decoder():  # pragma: no cover
                     pp = _pp(**pp_kwargs)
                     yield pp_console_row(
                         pp,
-                        oids=oids,
+                        oid_maps=oid_maps,
                         with_offsets=True,
                         with_blob=False,
                         with_colours=with_colours,
@@ -5371,7 +5728,7 @@ def main():  # pragma: no cover
     )
     parser.add_argument(
         "--oids",
-        help="Python path to dictionary with OIDs",
+        help="Python paths to dictionary with OIDs, comma separated",
     )
     parser.add_argument(
         "--schema",
@@ -5409,7 +5766,10 @@ def main():  # pragma: no cover
     args.DERFile.seek(args.skip)
     der = memoryview(args.DERFile.read())
     args.DERFile.close()
-    oids = obj_by_path(args.oids) if args.oids else {}
+    oid_maps = (
+        [obj_by_path(_path) for _path in (args.oids or "").split(",")]
+        if args.oids else ()
+    )
     if args.schema:
         schema = obj_by_path(args.schema)
         from functools import partial
@@ -5425,8 +5785,8 @@ def main():  # pragma: no cover
     obj, tail = schema().decode(der, ctx=ctx)
     print(pprinter(
         obj,
-        oids=oids,
-        with_colours=True if environ.get("NO_COLOR") is None else False,
+        oid_maps=oid_maps,
+        with_colours=environ.get("NO_COLOR") is None,
         with_decode_path=args.print_decode_path,
         decode_path_only=(
             () if args.decode_path_only is None else