Packed Encoding Rules
Encyclopedia
Packed encoding rules are ASN.1 encoding rules for producing a compact transfer syntax for data structures described in ASN.1, defined in 1994.
PER provides a much more compact encoding than BER
. It uses additional information, such as the lower and upper limits for numeric values, from the ASN.1 specification to represent the data units using the minimum number of bits. The compactness requires that the decoder knows the complete abstract syntax of the data structure to be decoded, however.
There are two variations of packed encoding rules: unaligned and aligned. With the unaligned encoding, the bits are packed with no regard for octet (byte) boundaries. With aligned encoding, certain types of data structures are aligned on octet boundaries, meaning there may be some number of wasted padding bits. Unaligned encoding uses the least number of bits, but presumably at some cost in processing time.
The packed encoding rules also define a restricted set of encoding rules, called CANONICAL-PER, which is intended to produce only a single possible encoding for any given data structure. CANONICAL-PER's role is therefore similar to the role of DER
or CER
.
Documents: ITU-T X.691, ISO 8825-2.
PER provides a much more compact encoding than BER
Basic Encoding Rules
The Basic Encoding Rules is one of the encoding formats defined as part of the ASN.1 standard specified by the ITU in X.690.-Description:...
. It uses additional information, such as the lower and upper limits for numeric values, from the ASN.1 specification to represent the data units using the minimum number of bits. The compactness requires that the decoder knows the complete abstract syntax of the data structure to be decoded, however.
There are two variations of packed encoding rules: unaligned and aligned. With the unaligned encoding, the bits are packed with no regard for octet (byte) boundaries. With aligned encoding, certain types of data structures are aligned on octet boundaries, meaning there may be some number of wasted padding bits. Unaligned encoding uses the least number of bits, but presumably at some cost in processing time.
The packed encoding rules also define a restricted set of encoding rules, called CANONICAL-PER, which is intended to produce only a single possible encoding for any given data structure. CANONICAL-PER's role is therefore similar to the role of DER
Distinguished Encoding Rules
Distinguished Encoding Rules , is a message transfer syntax specified by the ITU in X.690. The Distinguished Encoding Rules of ASN.1 is an International Standard drawn from the constraints placed on basic encoding rules encodings by X.509. DER encodings are valid BER encodings...
or CER
Canonical Encoding Rules
Canonical Encoding Rules is a message transfer syntax specified by the ITU in X.690. It is a restricted variant of Basic Encoding Rules for producing unequivocal transfer syntax for data structures described by ASN.1....
.
Documents: ITU-T X.691, ISO 8825-2.