asn1_der

Welcome to asn1_der 🎉

This crate provides a basic no_std-compatible, no-panic and zero-copy DER implementation. It is designed to be reliable and reasonable fast without getting too large or sacrificing too much comfort. To achieve this, asn1_der makes extensive use of the no-panic crate and offers slice-based object views to avoid allocations and unnecessary copies.

Example

use asn1_der::{
    DerObject,
    typed::{ DerEncodable, DerDecodable }
};

fn main() {
    /// An ASN.1-DER encoded integer `7`
    const INT7: &'static[u8] = b"\x02\x01\x07";

    // Decode an arbitrary DER object
    let object = DerObject::decode(INT7).expect("Failed to decode object");

    // Encode an arbitrary DER object
    let mut encoded_object = Vec::new();
    object.encode(&mut encoded_object).expect("Failed to encode object");

    // Decode a `u8`
    let number = u8::decode(INT7).expect("Failed to decode number");
    assert_eq!(number, 7);

    // Encode a new `u8`
    let mut encoded_number = Vec::new();
    7u8.encode(&mut encoded_number).expect("Failed to encode number");
}

For the (de-)serialization of structs and similar via derive, see serde_asn1_der.

Typed Implementations

There are also some direct DerDecodable/DerDecodable implementations for native Rust type equivalents:

• The ASN.1-BOOLEAN type as Rust-bool
• The ASN.1-INTEGER type as Rust-[u8, u16, u32, u64, u128, usize]
• The ASN.1-NULL type as either () or Option::None (which allows the encoding of optionals)
• The ASN.1-OctetString type as Vec<u8>
• The ASN.1-SEQUENCE type as SequenceVec(Vec<T>)
• The ASN.1-UTF8String type as String

No-Panic

asn1_der is designed to be as panic-free as possible. To ensure that, nearly every function is attributed with #[no_panic], which forces the compiler to prove that a function cannot panic in the given circumstances. However since no_panic can cause a lot of false-positives, it is currently only used by the CI-tests and disabled by default in normal builds. If you want to use this crate with no_panic enabled, you can do so by specifying the no_panic feature.

What No-Panic Does Not Cover

It is important to know that no_panic is no silver bullet and does not help against certain kinds of errors that can also happen in this crate. This especially includes:

• Dynamic memory allocation errors: Since it is not possible to predict memory allocation errors, everything that requires dynamic memory allocation is mutually exclusive to no_panic and will be omitted if no_panic is enabled.

  This crate might allocate memory in the following circumstances:

  • When writing to a dynamically allocating sink (e.g. Vec<u8>, VecBacking(Vec<u8>))
  • When decoding a native owned type such as Vec<u8>, SequenceVec(Vec<T>) or String
  • During error propagation

  If the crate is compiled without std enabled, it does performy any dynamic memory allocation directly by itself – however for foreign implementations passed to this crate may still allocate memory and fail (e.g. a custom Sink implementation).

• Stack overflows: Since the stack size is not necessarily known during compile time, it is not possible to predict stack overflow errors e.g. caused by recursion.

• Calls to abort or similar: Since calls to abort or similar do not trigger stack unwinding, they can also no be detected by no_panic. This also means that no_panic does not work for builds that use panic = "abort" in their config.

  This crate by itself does never call abort directly.

Due to the limitations described above, the following functions are mutually exclusive to no_panic and disabled if no_panic is set:

• Error stacking/propagation (propagate is a no-op if compiled with no_panic)
• The sink implementation for a byte vector (impl Sink for Vec<u8>)
• The VecBacking(Vec<u8>) type
• The native OctetString type which uses Vec<u8> (impl<'a> DerDecodable<'a> for Vec<u8> and impl DerEncodable for Vec<u8>)
• The native Sequence type wrapper SequenceVec since it is based upon Vec
• The native Utf8String type based upon String (impl<'a> DerDecodable<'a> for String and impl DerEncodable for String)

Zero-Copy

The crate is designed to be as much zero-copy as possible. In fact this means that the DerObject type and all typed views are zero-copy views over the underlying slice. Of course, zero-copy is not always reasonable: The new-constructors are not zero-copy because they construct a new object into a sink and the native type implementations are not zero-copy because they are either Copy-types (e.g. u128) or owned (e.g. String).

What happened to asn1_der_derive?

Since version 0.7.0, the asn1_der_derive-crates has been deprecated in favor of serde_asn1_der. If you have a specific use-case why you cannot use serde, let me know; it's probably not that hard to revive asn1_der_derive 😊