Status

This document explains how to create a new PGP key and break it in, gradually having it replace the old key. It is here for the information of committers who wish to change the PGP key they use at Apache (for example to sign releases with).

Contents

Important Note

If your key has been compromised, you MUST NOT use a transition period. You should immediately revoke the compromised key and create a new one. All web of trust links signed by the old key should be regarded as suspect. A completely new set of links MUST be re-established by meeting in person.

Motivation

When replacing one uncompromised key with a newer (typically longer) one, a transition period where both keys are trustworthy and participate in the web of trust allows - by trust transitivity - links to the old key to be used to trust signatures and links created by the new key. During a transition, both keys are trustworthy but only (the newer) one is actively used to sign documents and certify links in the web of trust.

This document describes how to use GnuPG to create a new key and manage the keys during this transition period.

Using A Single Keyring For Two Keys

It is best to use a single keyring containing both keys.

Generate New Key

The new key should be generated either:

• directly in the keyring containing the old key

• in a new keyring and then transferred to the keyring containing the old key

To generate a strong RSA key follow these instructions. If a separate keyring is used then follow these instructions to transfer it.

Both new and old keys should now be contained in the same keyring. Verify this by:

$ gpg --list-secret-keys  

alice/secring.gpg


sec   1024D/AD741727 2009-08-20
uid                  Alice Example (EXAMPLE OF OLD KEY) <alice@example.org>
ssb   1024g/268883A9 2009-08-20
sec   4096R/E2B054B8 2009-08-20
uid                  Alice Example (EXAMPLE NEW KEY) <alice@example.org>
ssb   4096R/4A6D5217 2009-08-20

Both new and old keys should be listed.

Open Interative Edit

Now a number of operations need to be performed on the new key. Though it's possible to perform them individually (saving and closing after each one) it is more convenient to use the interactive edit mode.

Start by opening an edit session on the new key, for example E2B054B8

$ gpg --edit-key E2B054B8
gpg (GnuPG) 1.4.9; Copyright (C) 2008 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Secret key is available.
pub  4096R/E2B054B8  created: 2009-08-20  expires: never       usage: SC

                     trust: unknown       validity: unknown
sub  4096R/4A6D5217  created: 2009-08-20  expires: never       usage: E 

[ unknown] (1). Alice Example (EXAMPLE NEW KEY) <alice@example.org>
Command> 

Trust The New Key

The new key needs to be marked as ultimately trusted in this keyring. This will ensure that the web of trust links signed by this key will be trusted automatically.

Command> trust
pub  4096R/E2B054B8  created: 2009-08-20  expires: never       usage: SC

                     trust: unknown       validity: unknown
sub  4096R/4A6D5217  created: 2009-08-20  expires: never       usage: E 

[ unknown] (1). Alice Example (EXAMPLE NEW KEY) <alice@example.org>

Please decide how far you trust this user to correctly verify other users'
keys
(by looking at passports, checking fingerprints from different sources,
etc.)
1 = I don't know or won't say
  2 = I do NOT trust
  3 = I trust marginally
  4 = I trust fully
  5 = I trust ultimately
  m = back to the main menu
Your decision? 5
Do you really want to set this key to ultimate trust? (y/N) y
pub  4096R/E2B054B8  created: 2009-08-20  expires: never       usage: SC

                     trust: ultimate      validity: unknown
sub  4096R/4A6D5217  created: 2009-08-20  expires: never       usage: E 

[ unknown] (1). Alice Example (EXAMPLE NEW KEY) <alice@example.org>
Please note that the shown key validity is not necessarily correct
unless you restart the program.

Sign New Key With Old

The new key should be signed with the old key (AD741727, say):

Command> sign AD741727

pub  4096R/E2B054B8  created: 2009-08-20  expires: never       usage: SC

                     trust: ultimate      validity: ultimate
Primary key fingerprint: FF96 6261 C995 1DDE BF34  5150 D5D2 BDB5 E2B0 54B8
 Alice Example (EXAMPLE NEW KEY) <alice@example.org>



Are you sure that you want to sign this key with your
key "Alice Example (EXAMPLE OF OLD KEY) <alice@example.org>"
(AD741727)
Really sign? (y/N) y
You need a passphrase to unlock the secret key for
user: "Alice Example (EXAMPLE OF OLD KEY) <alice@example.org>"
1024-bit DSA key, ID AD741727, created 2009-08-20

Check Preferences

Check that check that SHA-1 is avoided in the key preferences of both the new and old keys.

Complete Edit

It is convenient to add secondary user ids (for current email accounts) now.

Save changes (which exits edit mode):

Command> save

Whether To Sign The Old Key With The New

Arguments can be made for and against signing the old key with the new. The old key is less trustworthy now and will be revoked in future so signing it may be misleading for those unaware of the potential weaknesses. However, without this signature, signers of the new key will not receive the transitive benefit of the links made from the old key. Anyone who chooses not to sign the old key with the new should made efforts to resign links made by the old key with the new key.

Set Default To New Key

Next, the default key on the keyring needs to be changed from the old key to the new. This will ensure that all future signatures will - by default - use the new key. Though the old key can still be used for signing by explicitly specifying it, this use should be avoided since the signatures will be weak.

To make the new key the default, set the default-key in the gpg.conf configuration file. For example, to set the default to E2B054B8 add:

default-key E2B054B8

This setting can be tested by creating a test signature:

$ gpg --detach-sig --armor document

You need a passphrase to unlock the secret key for
user: "Alice Example (EXAMPLE NEW KEY) <alice@example.org>"
4096-bit RSA key, ID E2B054B8, created 2009-08-20

Verify that the new key has been chosen by default.

Upload Both Keys

Finish the process by uploading the new and old keys to the keyserver:

$ gpg --send-keys E2B054B8 AD741727

Create Backups

Follow these instructions.

Generate And Store Revocation Certificates

Follow these instructions to create and securely store generic revocation certificates for the new key.

Update Documents

The final stage in the process is to update documents containing references to the old key so that they contain both the new and old keys. For Apache documents, follow this checklist opting for the instructions appropriate for a transition (when given a choice).

For other documents:

• Those containing an export , should be updated with a dual export

• Those containing a fingerprint should be updated with both fingerprints

Web Of Trust

Read this guide to the Apache use of the web of trust and make arrangements for your new key to be included at the earliest opportunity.

How To Export Both New And Old Keys

During a transition period, a single export containing both new and old public keys should be used whenever an export is needed. To create a suitable export, supply both key IDs on the command line.

For example, to export keys AD741727 (old) and E2B054B8 (new) to FILENAME use:

$ gpg --export --armor --output FILENAME AD741727 E2B054B8

This exports only the public keys, and so isn't confidential. Everywhere the old public key was published should be replaced by this dual export.

How To Fingerprint New And Old Keys

During the transitions, both fingerprints should be used. For example, to fingerprint old key AD741727 and new key E2B054B8, use:

$ gpg --fingerprint AD741727 E2B054B8
pub   1024D/AD741727 2009-08-20
      Key fingerprint = CD0C 5281 D0A9 E963 19AF  F365 AD81 612A AD74 1727
uid                  Alice Example (EXAMPLE OF OLD KEY) <alice@example.org>
sub   1024g/268883A9 2009-08-20

pub   4096R/E2B054B8 2009-08-20
      Key fingerprint = FF96 6261 C995 1DDE BF34  5150 D5D2 BDB5 E2B0 54B8
uid                 Alice Example (EXAMPLE NEW KEY) <alice@example.org>
sub   4096R/4A6D5217 2009-08-20

So the fingerprints are:

• CD0C 5281 D0A9 E963 19AF F365 AD81 612A AD74 1727 for AD741727

• FF96 6261 C995 1DDE BF34 5150 D5D2 BDB5 E2B0 54B8 for E2B054B8

(For every fingerprint, the last 8 digits are the key ID.)