BTW, in order to get /anything/ installed using CPAN, it'll recommend you get Digest::MD5. The reason is that CPAN keeps the md5sums of every module around in order to be able to verify that your download was acatualy successful. (If there were download errors, the md5sum would be different.)

However, PGP in specific probably wants Digest::MD5 because PGP uses MD5 digests for some of it's work. (SHA-1 would be more secure, but PGP is older then SHA-1.)