Is there a good way to parse unsupported BER structures?

[danopia]

Hello, I'm here because I have an encoded BER payload that I wanted to access fields from, and this library has BER decoding functions. However the payload I'm trying to read seems quite nested and I'm wondering if there's a god way to access the fields I want.

First of all, here's an example payload I'm trying to decode:

-----BEGIN CERTIFICATE REQUEST-----
MIIC2DCCAcACAQAwODEVMBMGA1UECgwMc3lzdGVtOm5vZGVzMR8wHQYDVQQDDBZz
eXN0ZW06bm9kZTpwZXQtZnJhYm94MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIB
CgKCAQEAxSdplo8iOfkRqXpTHw4faFhmiXykKI47mUfL5VlXFTSDZ47W61zYcTcu
ABHLzBfUf+9T6wbRrwlNTyH0oXJ4QCVr1dIzF9k2RG/z51HiMY1UgZQ7dPC1k0cP
et2e7I6+nZYo+ZeTQodFDYnYgtgxFA1Q+qdjdV44O0oEfoJ1isLoZBFL7hp/aCA0
r1Pbyr+7eUsIbXcR4ahNqDKvP0ltXZFJZHTgiXbWTRfCxwtxSv3CjC4pfgaaFNaF
wEG9S45Rt251WWJuUg6fCr/jFD8RV8BuwPwKzH3b4oobbOtVp23G9psx7UAQTizy
kKCG6H1yJtrW7G19hW65cazKl1qKJwIDAQABoFswWQYJKoZIhvcNAQkOMUwwSjAb
BgNVHREEFDASggpwZXQtZnJhYm94hwQKBhoOMAkGA1UdEwQCMAAwEwYDVR0lBAww
CgYIKwYBBQUHAwEwCwYDVR0PBAQDAgXgMA0GCSqGSIb3DQEBCwUAA4IBAQAFsLL/
gTcGsy8frU4mwKo35znxz8Je9DpTBGAIbOr9BlQ+MTQu5KV0PrKw0w/JILRXAOKK
ukg8O3t64VlFcxpe4nv1MoUXLOoMTZrgwXVV2+gc2k+psNSam/EXd8JgMgrGfRT1
mAtWLsZhewAbW/8xc28AWtJ5YLlInGhgTFmFvarAB0nM+ZQ3HjL7+6EvlmynFLN9
aGc2Q79rGdrEEPhp9YH1sRlrsgayooC3vqmLgGWA0FFecsNL94F8FmO5vInk/+jr
bYWGwUvN/5dIoeqRGXsuTz+Tqr6t93PEk8WmNcnOWz7xyO0EZeOCWWZQ6iscTvhu
b3Cvp+rnl5ofRZgM
-----END CERTIFICATE REQUEST-----

After decoding the base64 to a UInt8Array I had to peel back FOUR layers of BER:

import { base64_to_binary }  from "https://deno.land/x/[email protected]/src/helper.ts";
const raw = base64_to_binary(`MIIC...ZgM`);

import { ber_decode, ber_simple } from "https://deno.land/x/[email protected]/src/rsa/basic_encoding_rule.ts";
const data1 = ber_simple(ber_decode(raw)) as any;
const data2 = ber_simple(ber_decode(data1[0][3])) as any;
const data3 = ber_simple(ber_decode(data2[1])) as any;
const data4 = ber_simple(ber_decode(data3[0][1])) as any;
console.log(data4); // Uint8Array(4) [ 10, 6, 26, 14 ]

That final variable is an IPv4 address that the CSR wants a certificate for, and is what I wanted to validate.

Is there a sane way to navigate structures like this? Or do I have to harden this method a bit and call it a day? I had some trouble using types as well as you can see, because only some are exported.

Thanks in advance for your time.