An Attack on CFB Mode Encryption as Used by OpenPGP.

Serge Mister Robert J. Zuccherato An Attack on CFB Mode Encryption as Used by OpenPGP. 82-94 2005 conf/sacrypt/2005 Selected Areas in Cryptography http://dx.doi.org/10.1007/11693383_6 db/conf/sacrypt/sacrypt2005.html#MisterZ05