Crate asn1_rs

Expand description

BER/DER Parsers/Encoders

A set of parsers/encoders for Basic Encoding Rules (BER [X.690]) and Distinguished Encoding Rules(DER [X.690]) formats, implemented with the nom parser combinator framework.

It is written in pure Rust, fast, and makes extensive use of zero-copy. A lot of care is taken to ensure security and safety of this crate, including design (recursion limit, defensive programming), tests, and fuzzing. It also aims to be panic-free.

This crate is a rewrite of der-parser to propose a more data-oriented API, and add generalized support for serialization.

Many ideas were borrowed from the crypto/utils/der crate (like the Any/TryFrom/FromDer mechanism), adapted and merged into a generalized BER/DER crate. Credits (and many thanks) go to Tony Arcieri for writing the original crate.

BER/DER parsers

BER stands for Basic Encoding Rules, and is defined in [X.690]. It defines a set of rules to encode and decode ASN.1 [X.680] objects in binary.

[X.690] also defines Distinguished Encoding Rules (DER), which is BER with added rules to ensure canonical and unequivocal binary representation of objects.

The choice of which one to use is usually guided by the speficication of the data format based on BER or DER: for example, X.509 uses DER as encoding representation.

The main traits for parsing are the FromBer and FromDer traits. These traits provide methods to parse binary input, and return either the remaining (unparsed) bytes and the parsed object, or an error.

The parsers follow the interface from nom, and the ParseResult object is a specialized version of nom::IResult. This means that most nom combinators (map, many0, etc.) can be used in combination to objects and methods from this crate. Reading the nom documentation may help understanding how to write and combine parsers and use the output.

Minimum Supported Rust Version: 1.53.0

Note: if the bits feature is enabled, MSRV is 1.56.0 (due to bitvec 1.0)

Examples

Parse 2 BER integers:

use asn1_rs::{Integer, FromBer};

let bytes = [ 0x02, 0x03, 0x01, 0x00, 0x01,
              0x02, 0x03, 0x01, 0x00, 0x00,
];

let (rem, obj1) = Integer::from_ber(&bytes).expect("parsing failed");
let (rem, obj2) = Integer::from_ber(&bytes).expect("parsing failed");

assert_eq!(obj1, Integer::from_u32(65537));

In the above example, the generic Integer type is used. This type can contain integers of any size, but do not provide a simple API to manipulate the numbers.

In most cases, the integer either has a limit, or is expected to fit into a primitive type. To get a simple value, just use the from_ber/from_der methods on the primitive types:

use asn1_rs::FromBer;

let bytes = [ 0x02, 0x03, 0x01, 0x00, 0x01,
              0x02, 0x03, 0x01, 0x00, 0x00,
];

let (rem, obj1) = u32::from_ber(&bytes).expect("parsing failed");
let (rem, obj2) = u32::from_ber(&rem).expect("parsing failed");

assert_eq!(obj1, 65537);
assert_eq!(obj2, 65536);

If the parsing succeeds, but the integer cannot fit into the expected type, the method will return an IntegerTooLarge error.

BER/DER encoders

BER/DER encoding is symmetrical to decoding, using the traits ToBer and ToDer traits. These traits provide methods to write encoded content to objects with the io::Write trait, or return an allocated Vec<u8> with the encoded data. If the serialization fails, an error is returned.