There was a bug in the old versions of PGP. It was discovered in version 2.2, and was corrected, somewhat in version 2.3. The bug was that the RSA-encoded certificated were actually in the reverse byte-order than they should have been, before they were encoded in the RSA encryption. This was somewhat corrected in 2.3, in that 2.3 could read the new, correct, pkcs_compatible signature, although PGP didn't start outputting this corrected signtature until 2.3a. PGP version 2.6 cannot read the old version. This means that anything that was created with versions before 2.3a cannot be read by version 2.6, and this is what you are seeing when you see "Malformed or obsolete signature format".. It is a signature that was created before 2.3a, and therefore 2.6 does not understand it. FYI: PGP 2.6 has a neat feature... If you recreate a signature in the new format, with a newer timestamp than an old signature, 2.6 will use the newer signature in lieu of the older signature when merging keyrings, so you can replace old signatures. -derek PS: This had to happen eventually.