Distinguished Encoding Rules

A subset of the Basic Encoding Rules that always provides only one way to encode any data structure defined by ASN.1. [X690].

Tutorial: For a data structure defined abstractly in ASN.1, BER often provides for encoding the structure into an octet string in more than one way, so that two separate BER implementations can legitimately produce different octet strings for the same ASN.1 definition. However, some applications require all encodings of a structure to be the same, so that encodings can be compared for equality. Therefore, DER is used in applications in which unique encoding is needed, such as when a digital signature is computed on a structure defined by ASN.1.