`GeneralizedTime` encodes unaccepted value.

[5225225]

My fuzzer for this was

#![no_main]
use libfuzzer_sys::fuzz_target;

fuzz_target!(|data: &[u8]| {
    if let Ok(value) = rasn::der::decode::<rasn::types::Open>(data) {
        assert_eq!(value, rasn::der::decode(&rasn::der::encode(&value).unwrap()).unwrap());
    }
});

Not sure if this a valid round fuzz test, feel free to close as invalid if not.

Reproducer is

fn main() {
    let data = [
        24, 19, 43, 53, 49, 54, 49, 53, 32, 32, 48, 53, 50, 52, 48, 57, 52, 48, 50, 48, 90,
    ];

    let value = rasn::der::decode::<rasn::types::Open>(&data).expect("passes");

    rasn::der::decode::<rasn::types::Open>(&rasn::der::encode(&value).unwrap()).expect("fails");
}

Fails with thread 'main' panicked at 'fails: NoValidChoice { name: "Open" }', src/main.rs:7:81

[XAMPPRocky]

Thank you for your issue! This seems maybe valid, it's definitely a difference at least, though I'm not sure why yet, and not entirely sure how to fix it.

The supplied data is a GeneralizedTime type encoded as +51615 0524094020Z, where once as it's decoded and re-encoded it's encoded +516150524094020Z (notice the missing space), which is then rejected by the decoder.

Here's the snippets of where this encoded/decoded.

https://github.com/XAMPPRocky/rasn/blob/441810cbaefddce2e2a6612acc73f2d5e1775707/src/ber/enc.rs#L340-L355

https://github.com/XAMPPRocky/rasn/blob/441810cbaefddce2e2a6612acc73f2d5e1775707/src/ber/de.rs#L290-L296

[Nicceboy]

I am trying to fix this, but it seems that the decoder is much more "loose", than the spec allows for GeneralizedTime.

If we go with the spec, it should be easy to handle all variations, but if we compare to other implementations (asn1tools), they handle more cases.
E.g. they accept both , comma and . dot, or missing seconds or minutes, or also +/- offsets in encoded values, while the BER should never produce such outputs.

Actually I think this applies only for CER and DER, but is missing from them. So I guess both are needed.