Dictionary.net

(CER) A restricted variant of BER forproducing unequivocal transfer syntax for data structuresdescribed by ASN.1.Whereas BER gives choices as to how data values may beencoded, CER and DER select just one encoding from thoseallowed by the basic encoding rules, eliminating all of theoptions. They are useful when the encodings must bepreserved, e.g. in security exchanges.CER and DER differ in the set of restrictions that theyplace on the encoder. The basic difference between CER andDER is that DER uses definitive length form and CER usesindefinite length form.Documents: ITU-T X.690, ISO 8825-1.See also PER.