All official releases of code distributed by the Apache Software Foundation
are signed by the release manager for the release. PGP signatures and MD5 and/or SHA1
hashes are available along with the distribution.
You should download the PGP signatures and MD5/SHA1 hashes directly from the
Apache Software Foundation rather than our mirrors. This is to help ensure the
integrity of the signature files. However, you are encouraged to download the
releases from our mirrors. (Our download page points you at the mirrors for
the release and the official site for the signatures, so this happens
automatically for you.)
File hashes are intended to be used to check that a file has been downloaded correctly.
They do not provide any guarantees as to the authenticity of the file.
A unix program called md5
or md5sum
is
included in many unix distributions. It is also available as part of
GNU
Textutils. Windows users can get binary md5 programs from here, here, or
here.
The following example details how signature interaction works.
The example is for the Apache HTTP Server project, but applies equally to other ASF projects.
In this example, you are already assumed to have downloaded
httpd-2.0.44.tar.gz
(the release) and
httpd-2.0.44.tar.gz.asc
(the detached signature).
This example uses The GNU Privacy Guard.
Any OpenPGP-compliant program should work
successfully.
First, we will check the detached signature
(httpd-2.0.44.tar.gz.asc
) against our release
(httpd-2.0.44.tar.gz
).
% gpg httpd-2.0.44.tar.gz.asc
gpg: Signature made Sat Jan 18 07:21:28 2003 PST using DSA key ID DE885DD3
gpg: Can't check signature: public key not found
This means that we don't have the release manager's public key (DE885DD3
) in
our local system. You now need to retrieve the public key from a key
server. One popular server is pgpkeys.mit.edu
(which has a web interface). The public key servers are
linked together, so you should be able to connect to any key server.
% gpg --keyserver pgpkeys.mit.edu --recv-key DE885DD3
gpg: requesting key DE885DD3 from HKP keyserver pgpkeys.mit.edu
gpg: trustdb created
gpg: key DE885DD3: public key "Sander Striker <striker@apache.org>" imported
gpg: Total number processed: 1
gpg: imported: 1
In this example, you have now received a public key for an entity known
as 'Sander Striker <striker@apache.org>' However, you have no way
of verifying this key was created by the person known as Sander Striker.
But, let's try to verify the release signature again.
% gpg httpd-2.0.44.tar.gz.asc
gpg: Signature made Sat Jan 18 07:21:28 2003 PST using DSA key ID DE885DD3
gpg: Good signature from "Sander Striker <striker@apache.org>"
gpg: aka "Sander Striker <striker@striker.nl>"
gpg: checking the trustdb
gpg: no ultimately trusted keys found
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
Fingerprint: 4C1E ADAD B4EF 5007 579C 919C 6635 B6C0 DE88 5DD3
At this point, the signature is good, but we don't trust this key. A good
signature means that the file has not been tampered with. However, due to the
nature of public key cryptography, you need to additionally verify that key
DE885DD3 was created by the real Sander Striker.
Any attacker can create a public key and upload it to the public key
servers. They can then create a malicious release signed by this fake key.
Then, if you tried to verify the signature of this corrupt release, it would
succeed because the key was not the 'real' key. Therefore, you need to
validate the authenticity of this key.
You may download public keys for the Apache project developers from our website
or retrieve them from the public PGP keyservers (see above).
However, importing these keys is not
enough to verify the integrity of the signatures. If a release verifies as
good, you need to validate that the key was created by an official
representative of the Apache HTTP Server Project.
The crucial step to validation is to confirm the key fingerprint of the
public key.
% gpg --fingerprint DE885DD3
pub 1024D/DE885DD3 2002-04-10 Sander Striker <striker@apache.org>
Key fingerprint = 4C1E ADAD B4EF 5007 579C 919C 6635 B6C0 DE88 5DD3
uid Sander Striker <striker@striker.nl>
sub 2048g/532D14CA 2002-04-10
A good start to validating a key is by face-to-face communication with
multiple government-issued photo identification confirmations. However, each
person is free to have their own standards for determining the authenticity of
a key. Some people are satisfied by reading the key signature over a telephone
(voice verification). For more information on determining what level of trust
works best for you, please read the GNU Privacy Handbook section on Validating other keys on
your public keyring.
Most of the Apache HTTP Server developers have attempted to sign each
others' keys (usually with face-to-face validation). Therefore, in order to
enter the web of trust, you should only need to validate one person in our
web of trust. (Hint: all of our developers' keys are in the KEYS file.)
For example, the following people have signed the public key for Sander
Striker. If you verify any key on this list, you will have a trust
path to the DE885DD3 key. If you verify a key that verifies one of the
signatories for DE885DD3, then you will have a trust path. (So on, and so
on.)
pub 1024D/DE885DD3 2002-04-10 Sander Striker <striker@apache.org>
sig E2226795 2002-05-01 Justin R. Erenkrantz
sig 3 DE885DD3 2002-04-10 Sander Striker
sig CD4DF205 2002-05-28 Wolfram Schlich
sig E005C9CB 2002-11-17 Greg Stein
sig CC8B0F7E 2002-11-18 Aaron Bannert
sig DFEAC4B9 2002-11-19 David N. Welton
sig 2 82AB7BD1 2002-11-17 Cliff Woolley
sig 2 13046155 2002-11-28 Thom May
sig 3 19311B00 2002-11-17 Chuck Murcko
sig 3 F894BE12 2002-11-17 Brian William Fitzpatrick
sig 3 5C1C3AD7 2002-11-18 David Reid
sig 3 E04F9A89 2002-11-18 Roy T. Fielding
sig 3 CC78C893 2002-11-19 Rich Bowen
sig 3 08C975E5 2002-11-21 Jim Jagielski
sig 3 F88341D9 2002-11-18 Lars Eilebrecht
sig 3 187BD68D 2002-11-21 Ben Hyde
sig 3 49A563D9 2002-11-23 Mark Cox
...more signatures redacted...
Since the developers are usually quite busy, you may not immediately find
success in someone who is willing to meet face-to-face (they may not even
respond to your emails because they are so busy!). If you do not have a
developer nearby or have trouble locating a suitable person, please send an
email to the address of the key you are attempting to verify. They may be able
to find someone who will be willing to validate their key or arrange alternate
mechanisms for validation.
Once you have entered the web of trust, you should see the following upon
verifying the signature of a release.
% gpg httpd-2.0.44.tar.gz.asc
gpg: Signature made Sat Jan 18 07:21:28 2003 PST using DSA key ID DE885DD3
gpg: Good signature from "Sander Striker <striker@apache.org>"
gpg: aka "Sander Striker <striker@striker.nl>"