Usage
One purpose of the machine was to search text for key words from a watchlist. From a single foreign cipher system, Harvest was able to scan over seven million decrypts for any occurrences of over 7,000 key words in under four hours.
The computer was also used for codebreaking, and this was enhanced by a system codenamed Rye, which allowed remote access to Harvest. According to a 1965 NSA report, "RYE has made it possible for the agency to locate many more potentially exploitable cryptographic systems and `bust' situations. Many messages that would have taken hours or days to read by hand methods, if indeed the process were feasible at all, can now be `set' and machine decrypted in a matter of minutes". Harvest was also used for decipherment of solved systems; the report goes on to say that, "Decrypting a large batch of messages in a solved system also being routinely handled by this system".
Harvest remained in use until 1976, having been in operation at the NSA for fourteen years. Part of the reason for its retirement was that some of the mechanical components of Tractor had worn beyond use, and there was no practical way to replace them. IBM declined to re-implement the architecture in a more modern technology.
Read more about this topic: IBM 7950 Harvest
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