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