Crate der_parser
source ·Expand description
DER Parser
A DER (X.690) parser, 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_der method.
However, it cannot fully parse all objects, especially those containing IMPLICIT, OPTIONAL, or
DEFINED BY items.
use der_parser::parse_der;
let bytes = [ 0x30, 0x0a,
0x02, 0x03, 0x01, 0x00, 0x01,
0x02, 0x03, 0x01, 0x00, 0x00,
];
let parsed = parse_der(&bytes);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:
use der_parser::*;
use nom::{IResult,Err,ErrorKind};
fn localparse_seq(i:&[u8]) -> IResult<&[u8],DerObject> {
parse_der_sequence_defined!(i,
parse_der_integer,
parse_der_integer
)
}
let bytes = [ 0x30, 0x0a,
0x02, 0x03, 0x01, 0x00, 0x01,
0x02, 0x03, 0x01, 0x00, 0x00,
];
let parsed = localparse_seq(&bytes);All functions return an IResult object from nom: the parsed
DerObject, an Incomplete value, or an error.
Notes
- The DER constraints are not enforced or verified. Because of that, this parser is mostly compatible with BER.
- 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
DerObject::as_u32(knowning that this method will return an error if the integer is too large), or use thebigintfeature of this crate and useDerObject::as_bigint.