A Layman's Guide to a
Subset of ASN.1, BER, and
DER
An RSA Laboratories Technical Note
Burton S. Kaliski Jr.
Revised November 1, 1993
*
Abstract. This note gives a layman's introduction to a subset of OSI's Abstract Syntax Notation One
(ASN.1), Basic Encoding Rules (BER), and Distinguished Encoding Rules (DER). The particular
purpose of this note is to provide background material sufficient for understanding and implementing the
PKCS family of standards.
1. Introduction
It is a generally accepted design principle that abstraction is a key to managing
software development. With abstraction, a designer can specify a part of a
system without concern for how the part is actually implemented or represented.
Such a practice leaves the implementation open; it simplifies the specification;
and it makes it possible to state "axioms" about the part that can be proved when
the part is implemented, and assumed when the part is employed in another,
higher-level part. Abstraction is the hallmark of most modern software
specifications.
One of the most complex systems today, and one that also involves a great deal
of abstraction, is Open Systems Interconnection (OSI, described in X.200). OSI is
an internationally standardized architecture that governs the interconnection of
computers from the physical layer up to the user application layer. Objects at
higher layers are defined abstractly and intended to be implemented with
objects at lower layers. For instance, a service at one layer may require transfer
of certain abstract objects between computers; a lower layer may provide
*
Supersedes June 3, 1991 version, which was also published as NIST/OSI Implementors' Workshop
document SEC-SIG-91-17. PKCS documents are available by electronic mail to <pkcs@rsa.com>.
Copyright
1991–
1993 RSA Laboratories, a division of RSA Data Security, Inc. License to copy
this document is granted provided that it is identified as "RSA Data Security, Inc. Public-Key
Cryptography Standards (PKCS)" in all material mentioning or referencing this document.
003-903015-110-000-000
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