There has been a notice of a breach (see: CVE-2007-4752) as to some binary content upstream of CentOS. I do not address that matter here beyond stating that the CentOS team have responded to the matter, and will continue this review process:
updated 22 Aug 2008 CentOS acknowledge CVE-2007-4752 and are reviewing our build and signing processes and hosts for signs of tampering subsequent to retrieval of SRPMs
It can be hard for a person to get a capsule writeup on signed content, and how to verify that it is indeed authentic. I have placed clearsigned content addressing this process at my personal domain webserver:
http://www.herrold.com/import-key-howto.txt.asc
and as an attachment to this email. I have verified that the copy at my site verifies. this email. Hopefully this attched writeup will transit the CentOS mailing list manager intact. I also include it inline below, but this may mangle the signature.
-- Russ herrold
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
A few minutes on using detached and clearsigned content.
In light of today's CVE-2007-4752 by the CentOS project's upstream: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-4752 I issue this brief piece on using GnuPG
1. View a proposed key to use, at the MIT keyserver
from: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x650D5882
2. Copy and create a local instance
[herrold@centos-5 redhat]$ vi rht-key
[herrold@centos-5 redhat]$ gpg --import rht-key gpg: key 650D5882: duplicated user ID detected - merged gpg: key 650D5882: public key "Red Hat, Inc. (Security Response Team) secalert@redhat.com" imported gpg: Total number processed: 1 gpg: imported: 1 gpg: 3 marginal(s) needed, 1 complete(s) needed, classic trust model gpg: depth: 0 valid: 2 signed: 5 trust: 0-, 0q, 0n, 0m, 0f, 2u gpg: depth: 1 valid: 5 signed: 2 trust: 0-, 0q, 0n, 1m, 4f, 0u gpg: next trustdb check due at 2009-03-14
3. Compute a local fingerprint of the candidate
[herrold@centos-5 redhat]$ gpg --fingerprint 650D5882 pub 1024D/650D5882 2001-11-21 Key fingerprint = 9273 2337 E5AD 3417 5265 64AB 5E54 8083 650D 5882 uid Red Hat, Inc. (Security Response Team) secalert@redhat.com sub 2048g/7EAB9AFD 2001-11-21
[herrold@centos-5 redhat]$
4. Compare and validate the fingerprint of the candidate against the RHT statement of the same fingerprint:
http://www.redhat.com/security/team/key/
5. You do NOT need to accept a key permanently to check signed content purportedly with it; consider the Red Hat notice at: http://www.redhat.com/security/data/openssh-blacklist.html
6. We can retrieve the checking script
wget https://www.redhat.com/security/data/openssh-blacklist-1.0.sh
and the (presumptively) signed checksum of that file
wget https://www.redhat.com/security/data/openssh-blacklist-1.0.sh.asc
This is called a detached signature
7. And then we can validate ('--verify') that the signature and the file were signed by a person in possession of the private key.
Hopefully that private key is itself protected, as behind one way firewalls, and with a 'pass phrase' which matches a known public (which we retrieved and added earlier). This procedural security process is followed by me [one way firewalls, and pass phrases, and other CentOS team members], along with other measures.
[herrold@centos-5 redhat]$ gpg --verify openssh-blacklist-1.0.sh.asc \ openssh-blacklist-1.0.sh gpg: Signature made Fri 22 Aug 2008 05:02:29 AM EDT using DSA key ID 650D5882 gpg: Good signature from "Red Hat, Inc. (Security Response Team) secalert@redhat.com" gpg: WARNING: This key is not certified with a trusted signature! gpg: There is no indication that the signature belongs to the owner. Primary key fingerprint: 9273 2337 E5AD 3417 5265 64AB 5E54 8083 650D 5882 [herrold@centos-5 redhat]$
8. As we have not indicated to gpg that we permanently trust this key, gpg adds the WARNING -- this is expected and correct under this outline. The validation checks out.
9. This file can be clearsigned -- the process we will follow is this:
[herrold@centos-5 .gnupg]$ gpg --clearsign import-key-howto.txt
You need a passphrase to unlock the secret key for user: "R P Herrold herrold@owlriver.com" 1024-bit DSA key, ID 9B649644, created 2003-02-09
File `import-key-howto.txt.asc' exists. Overwrite? (y/N) y [herrold@centos-5 .gnupg]$
10. That is, import-key-howto.txt is clearsigned, and a new file, import-key-howto.txt.asc, is produced. As I did it twice, to add this text, the warning about Overwriting a file appeared.
11. This is a non-detached (clearsigned, file, and might also be tested by retrieving the indicated key contents, and doing a '--verify'
12. As I have previously certified my own key, I can do it more simply locally:
[herrold@centos-5 .gnupg]$ gpg --verify import-key-howto.txt.asc gpg: Signature made Fri 22 Aug 2008 12:37:39 PM EDT using DSA key ID 9B649644 gpg: Good signature from "R P Herrold herrold@owlriver.com" [herrold@centos-5 .gnupg]$
Note that the TIME of the signing will vary, as I have to resign the file after adding this content.
13. Previously (prior to 22 Aug 2008), I have included my PGP details in every piece of email I send. Starting today, as to email originate; I will add another line with my GPG details as well. I will send this document to the main centos mailing list.
Date: Thu, 21 Aug 2008 17:43:28 -0400 (EDT) From: R P Herrold herrold@owlriver.com To: trading-shim general mailing list ts-general@trading-shim.org Subject: segmentation faults In-Reply-To: 1219351509.12150.18.camel@gb07 Message-ID: alpine.LRH.1.999.0808211742100.2443@arj.bjyevire.pbz References: 200808202117.m7KLH4rf011059@pippin.first.lan 20080820224216.GA11712@localhost alpine.LRH.1.10.0808202147340.28881@arj.bjyevire.pbz 1219351509.12150.18.camel@gb07 User-Agent: Alpine 1.999 (LRH 1145 2008-08-19) X-M: Go Blue X-OpenPGP-Key-ID: 0x7BFB98B9 MIME-Version: 1.0
In pine (alpine), one does this with Customized X-headers:
Customized Headers = X-M: Go Blue X-GnuPG-GPG-Key-ID: ox9B649644 X-OpenPGP-Key-ID: 0x7BFB98B9
This piece intentionally does not address CentOS response; a preliminary statement on this has been posted in the /topic of the IRC channel #centos on irc.freenode.org, and I have done a blog losting which is up at: http://planet.centos.org/
- -- Russ herrold herrold@owlriver.com herrold@centos.org security@centos.org