There is no easy way to do remote file authentication.

You can however send the file, followed by the MD5 checksum of the file in a signature file. (There are plenty of Perl sources on the net that does MD5 checksum.) The remote system has to somehow (via cron?) compute the MD5 checksum of the received file, and write an error/success file, which can be picked up by your FTP client program.

There is another method, which is to create a custom version of ProFTP server by adding implicit MD5 checksum (or CRC checksum, etc) at both the client and server end, and client and server can verify checksums of the received and sent file to tell whether the file has arrived properly (server after received the file, automatically compute the MD5 hash and send to client as part of the acknowledgement packet). That sound's like a very interesting approach. I will most likely to follow the second approach, and have some fun coding. :-)