Canonical Encoding Rules


Canonical Encoding Rules (CER) 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, Canonical Encoding Rules (together with DER) selects just one encoding from those allowed by the Basic Encoding Rules, eliminating rest of the options. Canonical Encoding Rules is useful when the encodings must be preserved, e.g. in security exchanges.[1]

Canonical Encoding Rules was designed for use with messages so huge that it is easiest to start encoding them before their entire value is fully available.

Canonical Encoding Rules is rarely used, as the industry has locked onto Distinguished Encoding Rules as the preferred means of encoding values for use in secure exchanges.

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