[PATCH] build: sign tarball instead of sha256sum
Daniel Kahn Gillmor
dkg at fifthhorseman.net
Fri Mar 15 08:35:46 PDT 2019
On Fri 2019-03-15 10:50:34 -0300, David Bremner wrote:
> Adam Majer <amajer at suse.de> writes:
>> The (my?) expectation is that a *.asc file is a detached signature.
>> That's why GPG is warning when it is not a detached signature. But I can
>> live with .sha256.asc if there is no .sha256 ;)
> Right, aren't detached signatures preferred in general? Or am I
> misremembering some gpg folklore?
Detached signatures are recommended for several reasons:
* They can handle non-textual data
* They are not confused by varying character sets/encodings of textual
* They clearly demarcate what is being signed (text documents with
inline signatures can include arbitrary cruft before the signed text,
or after the signature)
* gpg (and gpgv)'s API has traditionally been ambiguous about what it
means to say "gpg --verify foo.asc" depending on whether foo (without
the ".asc") exists. This API "shortcut" has a nasty failure mode,
because an attacker can ship you an arbitrary "foo" and an
inline-signed document as "foo.asc". in that case, you might be
surprised to find that while the signature verifies, it has nothing
to do with "foo".
I don't think these situations are relevant for the case of a signed
sha256sum file verified in a sensible way:
* we're dealing with textual data, guaranteed to be US-ASCII.
Verifiers can explicitly make that assumption.
* Modern versions of gpg (and gpgv) have an --output argument when
validating a signature, making it much easier to see what
specifically was signed, and avoiding any ambiguity about weird
"foo.asc + unrelated foo" use cases (see my use of --output in the
pipeline example upthread)
Detached signatures have the additional disadvantage of having to
juggle/coordinate more files when publishing or retrieving a new
For the sake of shipping fewer files with each release, i think it makes
sense to use a clearsigned *.sha256.asc.
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