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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.

Examples

Writing 2 BER integers:

use asn1_rs::{Integer, ToDer};

let mut writer = Vec::new();

let obj1 = Integer::from_u32(65537);
let obj2 = Integer::from_u32(65536);

let _ = obj1.write_der(&mut writer).expect("serialization failed");
let _ = obj2.write_der(&mut writer).expect("serialization failed");

let bytes = &[ 0x02, 0x03, 0x01, 0x00, 0x01,
               0x02, 0x03, 0x01, 0x00, 0x00,
];
assert_eq!(&writer, bytes);

Similarly to FromBer/FromDer, serialization methods are also implemented for primitive types:

use asn1_rs::ToDer;

let mut writer = Vec::new();

let _ = 65537.write_der(&mut writer).expect("serialization failed");
let _ = 65536.write_der(&mut writer).expect("serialization failed");

let bytes = &[ 0x02, 0x03, 0x01, 0x00, 0x01,
               0x02, 0x03, 0x01, 0x00, 0x00,
];
assert_eq!(&writer, bytes);

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

References

  • [X.680] Abstract Syntax Notation One (ASN.1): Specification of basic notation.
  • [X.690] ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER).

Modules

nom, eating data byte by byte

Macros

Helper macro to declare integers at compile-time

Helper macro to declare integers at compile-time

Structs

The Any object is not strictly an ASN.1 type, but holds a generic description of any object that could be encoded.

ASN.1 BITSTRING type

ASN.1 BMPSTRING type

ASN.1 BOOLEAN type

End-of-contents octets

ASN.1 ENUMERATED type

ASN.1 restricted character string type (GeneralString)

ASN.1 restricted character string type (GraphicString)

BER/DER object header (identifier and length)

ASN.1 restricted character string type (Ia5String)

ASN.1 INTEGER type

ASN.1 NULL type

ASN.1 restricted character string type (NumericString)

ASN.1 restricted character string type (ObjectDescriptor)

ASN.1 OCTETSTRING type

Object ID (OID) representation which can be relative or non-relative. An example for an OID in string representation is "1.2.840.113549.1.1.5".

Helper object to parse TAGGED OPTIONAL types (explicit or implicit)

ASN.1 restricted character string type (PrintableString)

The SEQUENCE object is an ordered list of heteregeneous types.

An Iterator over binary data, parsing elements of type T

The SEQUENCE OF object is an ordered list of homogeneous types.

The SET object is an unordered list of heteregeneous types.

The SET OF object is an unordered list of homogeneous types.

BER/DER Tag as defined in X.680 section 8.4

A builder for parsing tagged values (IMPLICIT or EXPLICIT)

Helper object for creating FromBer/FromDer types for TAGGED OPTIONAL types

ASN.1 restricted character string type (TeletexString)

ASN.1 UniversalString type

ASN.1 restricted character string type (Utf8String)

ASN.1 restricted character string type (VideotexString)

ASN.1 restricted character string type (VisibleString)

Enums

BER Object class of tag

Error types for DER constraints

The Err enum indicates the parser was not successful

The error type for operations of the FromBer, FromDer, and associated traits.

A type parameter for EXPLICIT tagged values.

A type parameter for IMPLICIT tagged values.

BER Object Length

Contains information on needed data if a parser returned Incomplete

An error for OID parsing functions.

ASN.1 REAL type

The error type for serialization operations of the ToDer trait.

Traits

Helper trait for creating tagged EXPLICIT values

Helper trait for creating tagged IMPLICIT values

Verification of DER constraints

Base trait for BER object parsers

Base trait for DER object parsers

A type parameter for tagged values either Explicit or Implicit.

Base trait for BER string objects and character set validation

Common trait for all objects that can be encoded using the DER representation

Functions

Type Definitions

Holds the result of parsing functions

A helper object to parse [ n ] EXPLICIT T OPTIONAL

A helper object to parse [ n ] IMPLICIT T OPTIONAL

Holds the result of BER/DER serialization functions

A specialized Result type for all operations from this crate.

Holds the result of BER/DER encoding functions

An Iterator over binary data, parsing elements of type T

A helper object to parse [ n ] EXPLICIT T

A helper object to parse [ n ] IMPLICIT T

Derive Macros