libder is a small library for encoding/decoding DER-encoded objects. It is expected to be able to decode any BER-encoded buffer, and an attempt to re-encode the resulting tree would apply any normalization expected by a DER decoder. The author's use is primarily to decode/encode ECC keys for interoperability with OpenSSL.
The authoritative source for this software is located at https://git.kevans.dev/kevans/libder, but it's additionally mirrored to GitHub for user-facing interactions. Pull requests and issues are open on GitHub.
libder is not intended to be a general-purpose library for working with DER/BER specified objects. It may provide some helpers for building more primitive data types, but libder will quickly punt on anything even remotely complex and require the library consumer to supply it as a type/payload/size triple that it will treat as relatively opaque (modulo some encoding normalization rules that can be applied without deeply understanding the data contained within).
libder also doesn't do strict validation of what it reads in today, for better or worse. e.g., a boolean may occupy more than one byte and libder will happily present it to the application in that way. It would be normalized on re-encoding to 0xff or 0x00 depending on whether any bits are set or not.