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From: Ferris Ellis <ferris@ferrisellis.com>
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Date: Fri, 9 Mar 2018 08:02:50 -0500
Message-Id: <E8AC11A9-84FB-4252-A0D3-7EB396C6DA1B@ferrisellis.com>
Subject: Re: [alpine-devel] Upgrading package signatures from SHA1 to SHA2 digest.
References: <257B6969-21FD-4D51-A8EC-95CB95CEF365@ferrisellis.com> <20180308145356.6355eafe@vostro.util.wtbts.net>
In-Reply-To: <20180308145356.6355eafe@vostro.util.wtbts.net>
To: alpine-devel@lists.alpinelinux.org

> On Mar 8, 2018, at 7:53 AM, Timo Teras <timo.teras@iki.fi> wrote:
>=20
> On Wed, 7 Mar 2018 18:28:49 -0500
> Ferris Ellis <ferris@ferrisellis.com> wrote:
>=20
>> ...
>>=20
>> I wanted to start a dialog about the possibility of moving to using
>> SHA2 digests (I would presume SHA256 would be the preferred option)
>> for signatures as SHA1 is deemed insecure by many and is being phased
>> out for most usage of PKI. This includes my use case, where the
>> crypto-service I have deliberately no longer offers signatures with
>> SHA1 digests and instead offers standard SHA2 digests.
>>=20
>> ...
>=20
> I have been working to update .apk and index formats to binary. I was
> hoping to do the hash algorithm change there. While I do have the
> design ready, and some code too, it's taking a bit more than expected.
>=20
> I am willing to accept backwards compatible patches at this point even
> for the current formats. The signatures could be pretty easily updated.
> Just add a new prefix type to identify the signatures as rsa-sha256 or
> similar.
>=20
> However, sign only the control.tar.gz part of apk. That in turn
> contains hash for the control.tar.gz part containing the package
> metadata. Changing this 'identity hash' from sha1 to sha256 would be
> more intrusive. Same applies to the individual file checksums kept in
> the file database for audit purposes. However, control.tar.gz does have
> stronger hash (sha256) for data.tar.gz which contains the actual file
> data content.
>=20
> Timo

Timo, thanks for sharing! I=E2=80=99m a little confused by your message. Can=
 you clarify what each of the hashes are? Including the =E2=80=98identity ha=
sh=E2=80=99 and =E2=80=98individual file checksums=E2=80=99? I=E2=80=99m sti=
ll new to the internals of apk packaging and am only aware of two hashes:

1. The RSA signature hash uses SHA1 as the hash for control.tar.gz.
2. Inside control.tar.gz is the .PKGINFO file which contains a SHA2-256 hash=
 of data.tar.gz

Also, as I mentioned in my last reply to A. Wilcox, I think since the RSA si=
gnature is ASN1 encoded. If so you shouldn=E2=80=99t need a new prefix type,=
 as the ASN1 blob states the hash that it contains. But please correct me if=
 I=E2=80=99m wrong on this! Just trying to be of help :)

Cheers,
Ferris=


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