ASN.1 defines a method for the specification and encoding of arbitrary data structures. ASN.1 is part of the
OSI model of protocol layers, it is located within the "presentation layer" (layer 6). The approach of ASN.1 is to define an abstract syntax for the specification of structured data, and encoding rules for transforming structured data into a binary representation (which can then be exchanged).
BER is the oldest encoding for ASN.1, and a subset of it (known as
DER) is used for
X.509 Certificates.