“Brainwallet” is a program that takes a passphrase (hopefully a good one) and deterministically creates a Bitcoin wallet. This wallet can be used for transactions, then deleted from the computer. To get access to the wallet again, you only need the passphrase to re-create it.

Does something similar exist for GPG? If yes, where can I get it?
If not, is it even possible to create such a program? Maybe it's just a bad idea?

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    $\begingroup$ I don't know whether it exists in GPG in a standardized interface/format, but the answer to whether it is possible is yes. Private keys usually get seeded with random data, but you could also deterministically create private keys for GPG use from a password. $\endgroup$ – orlp Oct 23 '13 at 9:10
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    $\begingroup$ Same problem as for all password based encryption, except a bit worse since it's not possible to use salts. So whenever practical, encrypt your private key with the password instead of using a password as seed. $\endgroup$ – CodesInChaos Oct 23 '13 at 14:05
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    $\begingroup$ @ralu The coding part is easy. Typical password quality is a problem, especially since you can't use salts. $\endgroup$ – CodesInChaos Oct 23 '13 at 19:55
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    $\begingroup$ I have done this. See my code here: stackoverflow.com/questions/21937369/… $\endgroup$ – spectator Feb 21 '14 at 23:32
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    $\begingroup$ @figlesquidge, I don't know about that. How to generate a gpg key from a passphrase seems more crypto than security. $\endgroup$ – RobKohr Mar 5 '14 at 20:23