Suprisingly, it does what the name says: decodes DER-encoded data.

Available for downloading on the Hel Repository.

The library returns a decoder function: decode(data: string, kwargs: table)

The first argument is the data that should be decoded. The second argument specifies additional parameters for the decoder.

Currently, only the content field is used: it's the table of tag codes that will be used in specified order.

E.g., if you run this piece of code:

decode(data, {context={
  0x02,
  0x09
}})

the first tag with the "context-specific" class will be decoded as an integer, and the second one will be decoded as a real number.

I use this library to decode X.509 certificates (the standard of a very common certificate encoding, e.g., used in TLS). You, though, may have your own ideas on how to use this library. :)

I'd not recommend to encode something with the DER, though, as it's not that space-efficient.

This program uses the Apache 2.0 license. The text of the license can be obtained here.