Generating a new keypair

The command-line option --gen-key is used to create a new primary keypair.

alice% gpg --gen-key gpg (GnuPG) 0.9.4; Copyright (C) 1999 Free Software Foundation, Inc. This program comes with ABSOLUTELY NO WARRANTY. This is free software, and you are welcome to redistribute it under certain conditions. See the file COPYING for details. Please select what kind of key you want: (1) DSA and ElGamal (default) (2) DSA (sign only) (4) ElGamal (sign and encrypt) Your selection?

GnuPG is able to create several different types of keypairs, but a primary key must be capable of making signatures. There are therefore only three options. Option 1 actually creates two keypairs. A DSA keypair is the primary keypair usable only for making signatures. An ElGamal subordinate keypair is also created for encryption. Option 2 is similar but creates only a DSA keypair. Option 4[1] creates a single ElGamal keypair usable for both making signatures and performing encryption. In all cases it is possible to later add additional subkeys for encryption and signing. For most users the default option is fine.

You must also choose a key size. The size of a DSA key must be between 512 and 1024 bits, and an ElGamal key may be of any size. GnuPG, however, requires that keys be no smaller than 768 bits. Therefore, if Option 1 was chosen and you choose a keysize larger than 1024 bits, the ElGamal key will have the requested size, but the DSA key will be 1024 bits.

About to generate a new ELG-E keypair. minimum keysize is 768 bits default keysize is 1024 bits highest suggested keysize is 2048 bits What keysize do you want? (1024)

The longer the key the more secure it is against brute-force attacks, but for almost all purposes the default keysize is adequate since it would be cheaper to circumvent the encryption than try to break it. Also, encryption and decryption will be slower as the key size is increased, and a larger keysize may affect signature length. Once selected, the keysize can never be changed.

Finally, you must choose an expiration date. If Option 1 was chosen, the expiration date will be used for both the ElGamal and DSA keypairs.

Please specify how long the key should be valid. 0 = key does not expire <n> = key expires in n days <n>w = key expires in n weeks <n>m = key expires in n months <n>y = key expires in n years Key is valid for? (0)

For most users a key that does not expire is adequate. The expiration time should be chosen with care, however, since although it is possible to change the expiration date after the key is created, it may be difficult to communicate a change to users who have your public key.

You must provide a user ID in addition to the key parameters. The user ID is used to associate the key being created with a real person.

You need a User-ID to identify your key; the software constructs the user id from Real Name, Comment and Email Address in this form: "Heinrich Heine (Der Dichter) <heinrichh@duesseldorf.de>" Real name:

Only one user ID is created when a key is created, but it is possible to create additional user IDs if you want to use the key in two or more contexts, e.g., as an employee at work and a political activist on the side. A user ID should be created carefully since it cannot be edited after it is created.

GnuPG needs a passphrase to protect the primary and subordinate private keys that you keep in your possession.

You need a Passphrase to protect your private key. Enter passphrase:

There is no limit on the length of a passphrase, and it should be carefully chosen. From the perspective of security, the passphrase to unlock the private key is one of the weakest points in GnuPG (and other public-key encryption systems as well) since it is the only protection you have if another individual gets your private key. Ideally, the passphrase should not use words from a dictionary and should mix the case of alphabetic characters as well as use non-alphabetic characters. A good passphrase is crucial to the secure use of GnuPG.