Gpg

Cheat sheet from Hera, by Philippe Teuwen.

setting this keyserver as default

• Edit {{file:~/.gnupg/gpg.conf}:

keyserver  hkp://hera.be-leu01.nxp.com

If you do so you won't need to specify the keyserver manually anymore as option in the commands given in the next sections.

On WinPT

• "Keyserver" menu → right-click somewhere in the white area → "Add" -> HKP Keyserver, Hostname: hera.be-leu01.nxp.com, Port: 11371 → "Add" → Select your keyserver and press "Set default".
• If you've previously set a proxy, be sure it's disabled (cf "Change proxy")

encrypting (and signing) a file

gpg [[--local-user|-u <yourself@nxp.com>] --sign|-s]  # if you want to sign (opt with another key than your main key)
    [--armor|-a]                                      # if you want to armor (ASCII) the output, else it's binary
    --encrypt|-e 
    --recipient|-r <someone@nxp.com> 
    [--encrypt-to <second_recipient@nxp.com>]         # if you want other people to be able to decrypt as well
    [--encrypt-to <yourself@nxp.com>]                 # if you want yourself to be able to decrypt as well
    [--output|-o <file.asc>]
    <file>

decrypting (and verifying) a file

gpg [--decrypt|-d]
    [--output|-o <file>]
    <file.asc>

So, yes, without any option gpg will decrypt/verify.

searching a key on the keyserver

gpg --keyserver hera.be-leu01.nxp.com
    --search <someone>                              # search only on full words

From here you can directly import a key by providing its numeral (1, 2, 3...)

importing a key from the keyserver

gpg --keyserver hera.be-leu01.nxp.com
    --recv-keys <key_id>                             # key-id is the last 8 bytes of the fingerprint

exporting a key to the keyserver

gpg --keyserver hera.be-leu01.nxp.com
    --send-keys <key_id>                             # key-id is the last 8 bytes of the fingerprint

importing a key from a file

gpg  --import <pubkey.asc>

exporting your publickey to a file

gpg  --armor|-a --output|-o <yourpubkey.asc> --export <yourself@nxp.com>

printing your fingerprint (e.g. to put in your mails footers)

gpg --fingerprint <yourself>|grep -i fingerprint

printing the fingerprint of an exported keyfile

gpg --with-fingerprint <exported_keyfile>|grep -i fingerprint

signing a key (see also below)

gpg --sign-key <someone>

Then you can upload it to the keyserver

On WinPT

When signing, don't forget to un-check the "Sign local only" box otherwise your signature cannot be exported to the server.

trusting a key owner

How far you trust this user to correctly verify other users' keys (by looking at passports, checking fingerprints from different sources, etc.)

gpg --edit-key <someone>

Command> trust
=> Choose the proper trust level
Command> quit
=> save changes

Remember that trust is not exported and purely local

revoking a subkey or a UID (old email address,...)

gpg --edit-key <yourself>

=> select UID(s) or subkey(s) by its numeral: 1, 2, 3...
Command> uid/key <n>
Command> revuid/revkey
Command> quit
=> save changes

Then you can upload it to the keyserver

extracting a session key

If you're forced to by a decryption order...

gpg --show-session-key --output|-o /dev/null <encrypted_file>

This will give you a long string: the session key. It can be used to decrypt that file

gpg --override-session-key <9:0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF>  <encrypted_file>

Installing GnuPG software

Under linux

• gnupg and many frontends are available for your favorite distribution
• quintuple-agent helps caching the passphrase
• gnupg can be configured through ~/.gnupg/gpg.conf with e.g.

keyserver hera.be-leu01.nxp.com
encrypt-to <yourself>

Under Windows

You can install everything at once via http://www.gpg4win.org Choose to install the following when prompted:

• GnuPG, of course
• WinPT, a GUI frontend offering a keyring manager and file en/decryption manager
• GPA, the Gnu Privacy Assistant, another keyring manager and file en/decryption manager
• GPGee, for integration of the gpg tools in the Windows Explorer
• Possibly GPGol or Claws if you use another MUA than Lotus Notes...

Creating keys

Creating fresh keys

Choose preferably RSA keys >= 2048 bits.

E.g. create first a RSA key for signing only then add a RSA encryption key:

gpg --expert --gen-key
# => RSA (sign only)
# => 2048 or bigger
# => validity: forever is ok
# => your name & email
# => choose a strong passphrase and be sure not to forget it!

gpg --edit-key <yourself>
# Command> addkey
# => re-type your passphrase
# => RSA (encrypt only)
# => 2048 or bigger
# => validity: forever is ok
# Command> quit
# => save changes

Importing a secret key from PGP

If you've already a PGP key you can import it into GnuPG: Under PGP, choose to export your key and ack to export also the secret key, tell where to put your ascii file, e.g. mykey.asc With GnuPG, import the ascii file with the following command:

gpg --import --allow-secret-key-import < <mykey.asc>

Recovering a public key from a secret key

In case you destroyed your public key and cannot fetch it from the keyserver, you can reconstruct it:

gpg --export-secret-key <myname> | gpgsplit --no-split --secret-to-public |gpg import

Generating a revocation certificate, just in case...

Print it and keep it safe in case your key is compromised or you definitively forgot your passphrase:

gpg --gen-revoke <yourself>

Signing keys the right way

Signing keys involve more than a few GPG commands as it implies trust. Get the public key of someone, either via keyserver or import file

• Get the owner of the key in contact with you
• Verify his identity (authenticate the owner)
• Show him the fingerprint of his key from your computer (when you want to sign the soft will show you the fingerprint)
• He must verify his fingerprint and make sure you are about to sign *his* key (the owner authenticates his key)
• Sign the key, in an exportable way
• Send the signed key to the server

Skipping the social aspect, a signature via gpg will look like:

gpg --keyserver hera.be-leu01.nxp.com --search <someone>
# either import interactively the key or find the key_id and get it:
gpg --keyserver hera.be-leu01.nxp.com --recv-keys <key_id>
gpg --sign-key <key_id>
gpg --keyserver hera.be-leu01.nxp.com --send-keys <key_id>