Is a secret key compromised by known cleartext?

[Konrad Podloucky]

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On Sat, 2003-05-31 at 10:14, tito@rumford.de wrote:
[...]
> If I got an email with a message in cleartext immediately=20
> followed by the same message encrypted to my public key --=20
> would that change the status of my secret key (being secret)=20
> abruptly to "being well known"?
>=20
Actually no. If all it took to get the private key was a
plaintext-ciphertext pair, the whole PGP concept would be pretty much
doomed. Everybody who sends you encrypted mail, has access to the
plaintext and ciphertext (because she/he generated both).

gpg takes the plaintext and encrypts it with a symmetric cipher by using
a random key. Then this random key is encrypted with your public key so
that you can decrypt the message. The symmetric algorithms used by gpg
are all immune against known-plaintext attacks.

hth,
	Konrad

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