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Remove implementation of deprecated PGP "quick check" #31
PGP's block cipher mode makes the first two bytes of the second block a duplicate of two bytes from the IV. This redundancy was included in PGP as a quick way to check the right decryption key is being used, but was later discovered to not be cryptographically secure -- in some cases it can be exploited to partially decrypt messages (https://eprint.iacr.org/2005/033). Modern, secure implementations don't use the check, so the two bytes are only there for backwards compatibility.
The OpenPGP standard now includes encryption with cryptographic hashes for integrity protection.