Thus, this list of potential problems and gotchas for a developer who is trying to be backward-compatible. PGP 5.x does not accept V4 signatures for anything other than key material. PGP 5.0 rejects an encrypted session key if the keylength differs from the S2K symmetric algorithm. This is a bug in its validation function. PGP 5.0 does not handle multiple one-pass signature headers and trailers.
All previous versions ignore the implied data type, and look directly at the packet data type.
There are a number of enhanced variants of PGP 2.6.x that have been modified for SHA-1 signatures. Neither PGP 5.x nor PGP 6.0 recognize Elgamal Encrypt and Sign keys. They only handle Elgamal Encrypt-only keys. Werner Koch , Remscheider Str. D sseldorf, Germany.