[openpgp] Re: Analysis document

On Thursday, July 10th, 2025 at 17:25, Andrew Gallagher wrote:

> If this were forbidden, it would add some novel failure modes. For example, if I sign over a UTF-8 document with a text signature, and it turns out that there is an invalid UTF-8 character in it (say, a mishandled surrogate), is the signature invalid? Even if there’s no malleability risk?

That's not a new question, due to the text in section 4.6 Falko quoted as saying:

> For text document signatures (type ID 0x01), the implementation MUST first canonicalize the document by converting line endings to <CR><LF> and encoding it in UTF-8 (see [RFC 3629]). The resulting UTF-8 byte stream is hashed.

So basically it's already forbidden, the main thing we're discussing is just to make it more explicit.

But also, forbidding signing over non-UTF-8 data doesn't automatically require failing to verify in that case, instead the verifier could just assume that the data that was signed over is UTF-8, and I think that'd probably be simplest & safest as well.

Best,
Daniel

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