Support PEM BER data with unparsed trailing data. #977
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- [asn1] Add `fromPemBer()` call that is more permissive than `fromDer()` and allows trailing data. - [RFC 7468](https://www.rfc-editor.org/rfc/rfc7468) PEM data is BER encoded. The RFC recommends to prefer DER over BER encoding throughout and is described in Appendix B. - PKCS#7 PEM data with trailing zeros appears in the wild. This may be intentional, but unneeded, padding. In any case, it should be accepted. - Recent `node-forge` releases made `fromDer` more strict to by default throw an error when not all data is decoded. `fromDer` is used in many places even for BER data, but in this case an alternate is needed to allow for at least this trailing data. - The API is named `fromPemBer` rather than `fromBer` since it is currently intended to handle only the subset of PEM BER that is DER data followed by possible unparsed bytes. - **NOTE**: This API may not handle all PEM BER data. If other data in wild is found that needs better support please file an issue with an example. - Calls to `asn1.fromDer` that occurred on data from `pem.decode()`, or similar, now use `asn1.fromPemBer` to be more permissive in allowing possible trailing or padding bytes. - [asn1] `fromDer` error message changed to reflect also using the API with BER data. Changed from `'Unparsed DER bytes remain after ASN.1 parsing.'` to `'Unparsed bytes remain after ASN.1 parsing.'`.
dlongley
requested changes
Apr 22, 2022
| * | ||
| * @return the parsed asn1 object. | ||
| */ | ||
| asn1.fromPemBer = function(bytes, options) { |
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This seems to break abstractions a little too much for my tastes. I understand the reasoning. I think that adding asn1.fromBer would be acceptable -- but we've always tried to avoid implementing an entire BER parser because it's usually not necessary, it's complicated, and a much bigger lift ... so that's not going to happen here.
Since this is PEM-specific, I would recommend that we add this utility only to pem.js instead. Perhaps renamed to pem.toAsn1() or pem.berToAsn1() or similar? Thoughts?
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The hope is this less strict parsing doesn't reintroduce the issues fixed in 1.3.x. I think this method of accepting unparsed trailing bytes for PEM data, still parsing by default as DER, and with the additional checks in 1.3.x, this should be ok.