GnuPG is a free clone of PGP (PrettyGoodPrivacy), cryptographic software.
To find it on Debian, do:
aptitude search gnupg
aptitude install gnupg
To use GnuPG first, you generate your key:
Please select what kind of key you want:
(1) RSA and RSA (default)
(2) DSA and Elgamal
(3) DSA (sign only)
(4) RSA (sign only)
Select # 1
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048)
Accept and press [ Enter ]
Please specify how long the key should be valid.
0 = key does not expire
Key is valid for? (0)
Key does not expire at all
Is this correct? (y/N)
You need a user ID to identify your key; the software constructs the user ID
from the Real Name, Comment and Email Address in this form:
"Heinrich Heine (Der Dichter)
Real name: [ Enter your name here ]
Email address: [ Enter your email address here ]
Comment: [ Enter a comment or leave blank ]
You selected this USER-ID:
Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit?
[ Press 'O' to accept settings ]
You need a Passphrase to protect your secret key.
[ Type a memorable phrase. You will need it later. ]
GnuPG will generate and display your key. Something like:
pub 2048R/8E6D74A2 2010-12-31
uid Your Name
sub 2048R/AD17E388 2010-12-31