Weak encryption keys

Jacob Bachmeyer jcb62281 at gmail.com
Mon Mar 22 20:34:00 CET 2021

jsmith9810--- via Gnupg-users wrote:
> Hello all,
> I have a private key protected by blowfish cipher that despite a random salt and several rounds of RIPEMD160 iterations is still considered "weak" by GnuPG and it refuses to do anything with it. When I try to import this key manually (--import), gpg throws a "weak encryption key" error and refuses to import it. ...which I find ironic, because it has no problem importing unprotected plain-text keys. Also, it's worth pointing out that GnuPG applies its default protection scheme to the private keys imported this way regardless of what encryption these keys used earlier - which means that the issue that it's complaining about will actually be resolved simply by importing this key.
> I still managed to force this key into GnuPG's private key store through the secring.gpg migration route which preserves the key in its openpgp-native format, but now gpg refuses any operation involving this private key - sign, encrypt, etc. It won't even let me change the password - which would actually make this issue go away. I tested with GnuPG 1.4.23 as well and it does not have a problem either importing or using this key.
> I am not looking for a solution as I can easily work around this problem by changing password using GnuPG 1.x prior to importing this key in GnuPG 2.x, but should this be logged as a product defect? This doesn't look like reasonable way to deal with these so-called "weak" encryption keys when importing these keys would actually address the issue at hand.
> Thanks!

The problem is that a private key protected by a weak cipher is still 
potentially compromised if an attacker can get any copy of the key prior 
to migrating it to a stronger cipher.  In other words, if an attacker is 
able to obtain your current key blob, the attacker can still compromise 
your key by cracking that copy, even after you have migrated your copy 
to a stronger wrapping.

If an attacker was interested in you, your key is lost and the best path 
forwards is to revoke it and generate a new key.  You could sign the new 
key with the old one before revoking the old key.

-- Jacob

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