On Mon, Jan 31, 2022 at 02:29:19PM -0500, Stefan Berger wrote: > > > don't think I realized there was a more direct, PKCS#7-less way to do it and > > > that IMA used that way.) However, it would be better to use this as an > > > opportunity to move people off of the built-in signatures entirely, either by > > > switching to a full userspace solution or by switching to IMA. > > If what we sign remains the same, then we could support multiple > > methods and use a selector to let fsverity_verify_signature() know > > how it should verify the signature. I don't know what would be a > > proper place for the selector. > > > > PKCS#7 seems ok, as it is used for kernel modules. IMA would be > > also ok, as it can verify the signature more directly. I would also > > be interested in supporting PGP, to avoid the requirement for > > Linux distributions to manage a secondary key. I have a small > > extension for rpmsign, that I would like to test in the Fedora > > infrastructure. > > > > Both the PKCS#7 and the PGP methods don't require additional > > support from outside, the functions verify_pkcs7_signature() > > and verify_pgp_signature() (proposed, not yet in the upstream > > kernel) would be sufficient. > > FYI: An empty file signed with pkcs7 and an ecc key for NIST p256 generates > a signature of size 817 bytes. If an RPM needs to carry such signatures on a > per-file basis we are back to the size increase of nearly an RSA signature. > I would say for packages this is probably too much size increase.. and this > is what drove the implementation of ECC support. I am getting 256 bytes for an ECC signature in PKCS#7 format: cd src/fsverity-utils make openssl ecparam -name prime256v1 -genkey -noout -out key.pem openssl req -new -x509 -key key.pem -out cert.pem -days 360 touch file ./fsverity sign file file.sig --key=key.pem --cert=cert.pem stat -c %s file.sig Probably you accidentally included the whole certificate in the PKCS#7 message. That's not required here. There are definitely problems with PKCS#7, and it does have space overhead. But the space overhead is not as bad as you state. - Eric
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