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rcp (remote copy) program was a tool for copying files to/from remote computers. It has since been superceded by ssh, particularly the scp tool. Everyone who still has
rcp enabled is encouraged to immediately disable it for important security reasons.
rcp tool was introduced in BSD Unix in the 1980s. It was an important tool at the time, but it suffered from several shortcomings. Its security was poor, and its usability wasn't great.
.rhosts files and
/etc/hosts.equiv for authentication. These methods relied on IP addresses and DNS (Domain Name System) for authentication. However, spoofing IP addresses is fairly easy, especially if the attacker is on the local network, and at the time it could even be done remotely.
.rhosts files were stored in users' home directories, which were typically stored on NFS (Network File System) volumes. The security of NFS at that time was poor (and still is, in many installations).
A major annoyance in
rcp was that it didn't support passwords for authentication. Whenever you wanted to copy files between systems, you first had to set up
.rhosts authentication. Besides obvious security implications, this was really cumbersome.
Making ad hoc copying of file easy was a major factor in the success of SSH. It being secure was just an added bonus. The ease of use meant students and employees could learn it more easily and there was less workload on IT support specialists. Lower costs, saved time, more productivity, better user satisfaction.