This is a Rust library for parsing and generating ASN.1 data (DER only).

Add asn1 to your Cargo.toml:

$ cargo add asn1

Builds on Rust 1.74.0 and newer.

rust-asn1 is compatible with #![no_std] environments:

$ cargo add asn1 --no-default-features

• Writer now exposes write_explicit_element and write_implicit_element methods that allow encoding EXPLICIT/IMPLICIT elements when the tag number is not known at compile time.

• Added Asn1Writable::encoded_length, SimpleAsn1Writable::data_length, and Asn1DefinedByWritable::encoded_length. Implementing these functions reduces the number of re-allocations required when writing. None can be returned if it is not possible to provide an efficient implementation.

• Updated MSRV to 1.74.0.

• BitString::new is now const fn.

• BigInt::new, BigUint::new, and DateTime::new are now const fn.

• Parser now exposes a peek_tag method that returns the tag of the next element in the parse, without consuming that element. (#532)
• Parser now exposes read_explicit_element and read_implicit_element methods that allow parsing EXPLICIT/IMPLICIT elements when the tag number is not known at compile time.
• PrintableString, Utf8String, BMPString, and UniversalString now #[derive(Hash)]. (#536)

• Updated MSRV to 1.65.0.

• Fixed "perfect derives" in conjunction with #[derive(Asn1DefinedByRead)] and #[derive(Asn1DefinedByWrite)]. (#506)

• Removed Writer::{write_explicit_element, write_optional_explicit_element, write_implicit_element, write_optional_implicit_element}. These can all be better accomplished with the asn1::Explicit and asn1::Implicit types.

• Fixed "perfect derives" in conjunction with #[implicit] and #[explicit]. (#502)

• GeneralizedTime has been renamed to X509GeneralizedTime. The type does not allow fractional seconds, however this restriction is not actually a DER rule, it is specific to X.509. (#494)

• GeneralizedTime is a new type that accepts fractional seconds replacing the old GeneralizedTime. (#492)

• #[derive(asn1::Asn1Read)] and #[derive(asn1::Asn1Write)] now implement "perfect derives". (#496)