simple-tlv

Encoding and decoding of SIMPLE-TLV as described in ISO 7816-4, without allocations.

Follows the approach taken in der.

License

^{simple-tlv is licensed under either of Apache License, Version 2.0 or MIT License at your option.}
_{Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.}

lib.rs:

simple-tlv

Implementation of the SIMPLE-TLV serialization format from ISO 7816-4:2005.

5.2.1 SIMPLE-TLV data objects

Each SIMPLE-TLV data object shall consist of two or three consecutive fields: a mandatory tag field, a mandatory length field and a conditional value field. A record (see 7.3.1) may be a SIMPLE-TLV data object.

• The tag field consists of a single byte encoding a tag number from 1 to 254. The values '00' and 'FF' are invalid for tag fields. If a record is a SIMPLE-TLV data object, then the tag may be used as record identifier.
• The length field consists of one or three consecutive bytes.
  • If the first byte is not set to 'FF', then the length field consists of a single byte encoding a number from zero to 254 and denoted N.
  • If the first byte is set to 'FF', then the length field continues on the subsequent two bytes with any value encoding a number from zero to 65,535 and denoted N.
• If N is zero, there is no value field, i.e., the data object is empty. Otherwise (N > 0), the value field consists of N consecutive bytes.

Credits

This library is a remix of RustCrypto/utils/der, with a view towards:

• not requiring references to ASN.1 (e.g., since SIMPLE-TLV does not have any)
• not requiring allocations or memmoves (like ring, derp, x509:der)
• adding a type layer on top of SIMPLE-TLV's byte slice values

The core idea taken from der is to have Encodable require an encoded_length method. By calling this recursively in a first pass, allocations required in other approaches are avoided.