How to read a PGP-encrypted email from the command-line

I received a PGP-encrypted email a couple days ago with confidential information. As I use GMail, I do not have direct support for PGP. Here are the steps I followed in order to extract the message and the files in it, from the command-line.

Disclaimer: I already knew the big picture for PGP but it was the first time I had to effectively use it.

The message was empty with just a msg.asc file in it:

$ head msg.asc 
-----BEGIN PGP MESSAGE-----
Version: GnuPG v1

hQEMA5Rm9tOuXUEGAQgAlcrBh++K7tBf6UhLPR3MM1S3N94xfSRamHWLXMBj5dp6
9fg+a2GuQDRnta+QRgmlkgXha/6vU9eFzqx9Fh7neeFOC2aOc+8wq7KSNXjUaX0o
wRdm1Jbh7fKy9ygNKGcTkikrpuVtYj1GrLjKD5CJ0gdGvv9vQIr8bUuVE+WwKgOr
hIv4sWDXChiWahDtY8A/LktfAWd0eVZ47FzQQ/LKo89v8POxvqPACmyzDRNKkNhy
AJSu2kjA44k/f79n880lMKZ89GMYjzKISxkxWYi4ccZPOmXgYFIrx5SFDhJNPhaw
1gd3InrLpBdTYGuJZxwRcZ1SpY4v5siDLoXQHnuHONLtAZh02Viq/F0cwWuRyMk5
km2lb3OREW2bHEzHTL5U4/Vb71cup0U7js7J7WvxOR7TCzizShX4w+uRAbfuLmH+

So I basically knew this had been encrypted using PGP with my public PGP key. I already had one because I need to sign artifacts when publishing on Sonatype.

First, I install the GPG toolkit for Ubuntu:

$ sudo apt-get install pgpgpg

Then I get the sender’s public key from his website and add it to my keyring (source):

$ pgp -ka send.pubkey

And I can finally extract the content.

$ pgp msg.asc

The resulting file msg is a typical email attachment:

Content-Type: multipart/mixed; boundary="a8Wt8u1KmwUX3Y2C"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit


--a8Wt8u1KmwUX3Y2C
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit

...

--a8Wt8u1KmwUX3Y2C
Content-Type: application/pdf
Content-Disposition: attachment; filename="the-file.pdf"
Content-Transfer-Encoding: base64

...

--a8Wt8u1KmwUX3Y2C--

I still need to extract the PDF. For that, I used munpack:

$ sudo apt-get install mpack
$ munpack msg
the-file.pdf (application/pdf)

Et voilà!

Bonus

If you have forgotten your passphrase to unlock your PGP key, you can use this command found on stackoverflow:

$ echo "1234" | gpg --no-use-agent -o /dev/null --local-user 'Alexandre Bertails <alexandre@bertails.org>' --no-greeting -as - && echo "The correct passphrase was entered for this key"

You can also use the --passphrase parameter if needed.