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Bad Session Key error when trying to decrypt a file encrypted with Robo-FTP
This article applies to Robo-FTP v3.6 and later.
Recipients using very old versions of PGP Desktop may not be able to decrypt files encrypted with Robo-FTP.
The most common error users report is Bad Session Key, but the error message may vary depending on the version of PGP Desktop (or other PGP implementation) being used.
If you encounter this problem you can use the /compat option with PGPENCRYPT to create PGP Desktop 2.x compatible files.
Using this older PGP format is still generally considered to be secure, but it does impose a 2 Gb file size limit.
If you are signing a file in addition to encrypting it, and the recipient's PGP implementation is particularly old, using the /compat option with PGPENCRYPT may not be sufficient. You may also need to generate a new key pair using the "Old PGP key compatibility" option in the Configurator. Use this key for signing and encrypting the file (and be sure to send the resulting public key to the recipient).
Article last updated: 2021-01-15
Tags: PGP, GPG, Encryption