GnuPG Preferences

Many GnuPG users do not set the preferences for cipher, hash and compression algorithms – at least that is my impression. Therefore quite a few users have unwanted or unexpected preferences and do not always know how to change them.

Pointing these users to the documentation may be helpful but there’s no step by step instruction of how to change preferences. However, this is what this document does.

Note: The following works with GnuPG 1.0.7 or later, BZIP2 compression method works with GnuPG 1.2.4 or later (see Change preferences).

To check the supported algorithms of your GnuPG installation just enter the command gpg –version:

Lines beginning with Cipher:, Hash: and Compress: are of interest.

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To enter the GnuPG interface for editing keys just fire gpg –edit-key Key-ID:

To examine the current preferences you can use the command pref. However, showpref will generate an output that is easier to understand:

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To change the preferences you will have to use the command setpref. This command expects a list of preferred algorithms as argument. These algorithms have to be encoded as shown in the following table:

Note: The BZIP2 compression method is supported since GnuPG 1.2.4.

To set AES as preferred cipher algo followed by TWOFISH, CAST5, BLOWFISH and 3DES the sequence S7 S10 S3 S4 S2 has to be used. You can append the codes for your preferred hash and compression algos, e.g. if you like to have SHA1, RIPEMD160, MD5 as hash algos and ZLIB, ZIP as compression algos your complete sequence should look like this: S7 S10 S3 S4 S2 H2 H3 H1 Z2 Z1. This sequence is used as argument for setpref:

The command shown above sets preferences for all three keys in the keyring. To set preferences for a single key you will have to select the key by entering the appropriate number prior to the setpref command.

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To finally update your newly set preferences enter the command updpref:

This command requires you to enter your passphrase. Next, you can check your new preferences with pref or showpref and quit the interface with quit (confirm that you want to save the changes).

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GnuPG Homepage
GnuPG Documentation
GnuPG FAQ
GnuPG Mini Howto
GnuPG Manual

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