Canonical Encoding Rules
Encyclopedia
Canonical Encoding Rules (CER) is a message transfer syntax specified by the ITU
in X.690. It is a restricted variant of Basic Encoding Rules
for producing unequivocal transfer syntax for data structures described by ASN.1
.
Whereas BER
gives choices as to how data values may be encoded, CER and DER
select just one encoding from those allowed by the basic encoding rules, eliminating all of the options. They are useful when the encodings must be preserved, e.g. in security exchanges.
CER and DER
differ in the set of restrictions that they place on the encoder. The basic difference between CER and DER is that DER uses definitive length form and CER uses indefinite length form in some precisely defined cases. That is, DER always has leading length information, while CER uses the end-of-contents octet instead of providing the length of the encoded data. Because of this, CER requires less metadata for large encoded values, while DER does it for small ones.
Documents: ITU-T X.690, ISO 8825-1.
International Telecommunication Union
The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...
in X.690. It is a restricted variant of Basic Encoding Rules
Basic Encoding Rules
The Basic Encoding Rules is one of the encoding formats defined as part of the ASN.1 standard specified by the ITU in X.690.-Description:...
for producing unequivocal transfer syntax for data structures described by ASN.1
Abstract Syntax Notation One
Data generated at various sources of observation need to be transmitted to one or more locations that process it to generate useful results. For example, voluminous signal data collected by a radio telescope from outer space. The system recording the data and the system processing it later may be...
.
Whereas BER
Basic Encoding Rules
The Basic Encoding Rules is one of the encoding formats defined as part of the ASN.1 standard specified by the ITU in X.690.-Description:...
gives choices as to how data values may be encoded, CER and DER
Distinguished Encoding Rules
Distinguished Encoding Rules , is a message transfer syntax specified by the ITU in X.690. The Distinguished Encoding Rules of ASN.1 is an International Standard drawn from the constraints placed on basic encoding rules encodings by X.509. DER encodings are valid BER encodings...
select just one encoding from those allowed by the basic encoding rules, eliminating all of the options. They are useful when the encodings must be preserved, e.g. in security exchanges.
CER and DER
Distinguished Encoding Rules
Distinguished Encoding Rules , is a message transfer syntax specified by the ITU in X.690. The Distinguished Encoding Rules of ASN.1 is an International Standard drawn from the constraints placed on basic encoding rules encodings by X.509. DER encodings are valid BER encodings...
differ in the set of restrictions that they place on the encoder. The basic difference between CER and DER is that DER uses definitive length form and CER uses indefinite length form in some precisely defined cases. That is, DER always has leading length information, while CER uses the end-of-contents octet instead of providing the length of the encoded data. Because of this, CER requires less metadata for large encoded values, while DER does it for small ones.
Documents: ITU-T X.690, ISO 8825-1.