Canonical Encoding Rules

pyasn1.codec.cer.encoder.encode(value, asn1Spec=None)

Turns ASN.1 object into CER octet stream.

Takes any ASN.1 object (e.g. PyAsn1Item derivative) walks all its components recursively and produces a CER octet stream.

Parameters

value (either a Python or pyasn1 object (e.g. PyAsn1Item derivative)) – A Python or pyasn1 object to encode. If Python object is given, asnSpec parameter is required to guide the encoding process.

Keyword Arguments

asn1Spec – Optional ASN.1 schema or value object e.g. PyAsn1Item derivative

Returns

bytes (Python 3) or str (Python 2) – Given ASN.1 object encoded into BER octet-stream

Raises

PyAsn1Error – On encoding errors

Examples

Encode Python value into CER with ASN.1 schema

>>> seq = SequenceOf(componentType=Integer())
>>> encode([1, 2, 3], asn1Spec=seq)
b'0\x80\x02\x01\x01\x02\x01\x02\x02\x01\x03\x00\x00'

Encode ASN.1 value object into CER

>>> seq = SequenceOf(componentType=Integer())
>>> seq.extend([1, 2, 3])
>>> encode(seq)
b'0\x80\x02\x01\x01\x02\x01\x02\x02\x01\x03\x00\x00'

pyasn1.codec.cer.decoder.decode(substrate, asn1Spec=None)

Turns CER octet stream into an ASN.1 object.

Takes CER octet-stream and decode it into an ASN.1 object (e.g. PyAsn1Item derivative) which may be a scalar or an arbitrary nested structure.

Parameters

substrate (bytes (Python 3) or str (Python 2)) – CER octet-stream

Keyword Arguments

asn1Spec (any pyasn1 type object e.g. PyAsn1Item derivative) – A pyasn1 type object to act as a template guiding the decoder. Depending on the ASN.1 structure being decoded, asn1Spec may or may not be required. Most common reason for it to require is that ASN.1 structure is encoded in IMPLICIT tagging mode.

Returns

tuple – A tuple of pyasn1 object recovered from CER substrate (PyAsn1Item derivative) and the unprocessed trailing portion of the substrate (may be empty)

Raises

PyAsn1Error, SubstrateUnderrunError – On decoding errors

Examples

Decode CER serialisation without ASN.1 schema

>>> s, _ = decode(b'0\x80\x02\x01\x01\x02\x01\x02\x02\x01\x03\x00\x00')
>>> str(s)
SequenceOf:
 1 2 3

Decode CER serialisation with ASN.1 schema

>>> seq = SequenceOf(componentType=Integer())
>>> s, _ = decode(b'0\x80\x02\x01\x01\x02\x01\x02\x02\x01\x03\x00\x00', asn1Spec=seq)
>>> str(s)
SequenceOf:
 1 2 3