jsmith9...@gmx.com wrote:
[...]
A private key protected by weak blowfish cipher is by no means more at risk
compared to an unencrypted key, which GnuPG has no problem with.
The difference is that you *know* an unencrypted key is lying around at
risk of compromise, and you knowingly chose to take that risk when you
chose to store the key unencrypted.
Also, from what I've read about blowfish weak keys (and I admit I didn't spend
too much time on it), the attacks are unrealistic in that even though they
reduce the complexity compared to brute forcing a 128-bit key, it's still
near-impossible to retrieve the plain-text or the key itself within reasonable
amount of time. And I also recall reading that it requires a large amounts of
known plain-text and corresponding cipher-text data. In this case, it's a
unique key that's only used to encrypt a few hundred bytes of data. So the risk
of an attacker being able to just "crack" your private key based on the weakness
of the cipher key seems to be quite an overstatement.
I am assuming that there is some more severe problem with OpenPGP
Blowfish key wrapping, since the situation you describe would not
warrant the measures GPG has taken. (In other words, I am assuming that
the GPG developers know something here that we do not, and I believe
that to be a reasonable assumption.)
Besides, shouldn't the assessment of the security of the key be better left to
the user? It would be totally reasonable to warn the user about the potential
risks and even make a recommendation to revoke this key. But not allowing them
to decrypt something that was previously encrypted with this key doesn't seem
justifiable even if the risks were as high as you stated.
You are correct that the situation you describe does not reasonably
support completely rejecting the key. That is the reason I expect that
there is a problem serious enough that the key should be considered
compromised.
-- Jacob
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