BER/DER Parser
A parser for Basic Encoding Rules (BER [X.690]) and Distinguished Encoding Rules(DER [X.690]), implemented with the nom parser combinator framework.
The code is available on Github and is part of the Rusticata project.
DER parser design
There are two different approaches for parsing DER objects: reading the objects recursively as long as the tags are known, or specifying a description of the expected objects (generally from the ASN.1 description).
The first parsing method can be done using the parse_ber
and
parse_der
methods.
However, it cannot fully parse all objects, especially those containing IMPLICIT, OPTIONAL, or
DEFINED BY items.
# extern crate der_parser;
use parse_der;
#
The second (and preferred) parsing method is to specify the expected objects recursively. The
following macros can be used:
parse_der_sequence_defined
and similar functions,
parse_der_struct
, etc.
For example, to read a sequence containing two integers:
# extern crate nom;
# extern crate rusticata_macros;
# extern crate der_parser;
use *;
use ;
#
All functions return an IResult
object from nom
: the parsed
BerObject
, an Incomplete
value, or an error.
Notes
- The DER constraints are verified if using
parse_der
. BerObject
andDerObject
are the same objects (type alias). The only difference is the verification of constraints during parsing.- DER integers can be of any size, so it is not possible to store them as simple integers (they
are stored as raw bytes). To get a simple value, use
BerObject::as_u32
(knowning that this method will return an error if the integer is too large),BerObject::as_u64
, or use thebigint
feature of this crate and useBerObject::as_bigint
.