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Encryption Program Released

By Daniel C. Stevenson
Associate News Editor

Last month MIT issued a new, free version of the popular data encryption program PGP, which stands for "pretty good privacy."

The release of the PGP Version 2.6 software resolved a potential patent conflict between an older version of PGP and patents held by MIT and Stanford University for the RSA data encryption algorithm used by PGP. The new version resolves this conflict by granting a free license for non-commercial use of the software package on computer networks in the United States.

Encryption programs such as PGP are used to protect files and electronic messages so that only the intended recipient can decode the document. Encryption is also used to authenticate the sender of electronic messages.

MIT holds the 1983 RSA patent and exclusively licensed it to Public Key Partners of California for sale and sub-licensing of the RSA public key cryptosystem. PGP was written by Philip Zimmerman, a private programmer, using an independently developed implementation of the RSA algorithm, Zimmerman wrote in the PGP Version 2.6 manual.

Public Key Partners contended that Zimmerman's PGP conflicted with the RSA patent license, though Zimmerman said he is "convinced that publishing PGP the way I did does not violate patent law." Since May 22, Zimmerman has been the target of a U.S. Customs criminal investigation regarding the export controls on encryption software, according to the manual.

An information document about PGP provided by MIT and written by Professor of Electrical Engineering and Computer Science Harold Abelson '73, Jeffrey I. Schiller '79 of Information Systems, Brian A. LaMacchia G, and Derek A. Atkins G said that using the older versions of PGP "potentially infringes patents licensed exclusively to Public Key Partners" and the "sticky patent situation has deterred the spread of PGP."

"This agreement [to release a free version of PGP] solves the problem of software being distributed on the Internet which potentially infringed the intellectual property of MIT and the licensee, RSA," said Vice President for Information Systems James D. Bruce '60.

PGP uses public key encryption

Conventional "single-key" cryptosystems use one key to code and decode data, according to Zimmerman. To ensure privacy, this single key must be transmitted via secure channels so both parties are using the same key to decode the actual message, which could be sent over insecure channels.

Public key encryption allows people to "exchange files or messages with privacy, authentication, and convenience," Zimmerman wrote in the PGP manual. Public key encryption does not require secure channels because every user has two keys: a private key and a public key.

The public and private keys complement each other by unlocking the code that the other makes, Zimmerman said. In addition, knowledge of the public key does not aid in discovering the private key, allowing the public key to be widely distributed.

A message sender encrypts a message with the recipient's public key so that only the recipient can decode the message using their private key. Alternatively, the sender can encrypt a message with their private key, which can then only be decoded with the public key. This provides for authentic digital "signatures" of messages and files, Zimmerman said.

September format change

A deliberate change to PGP Version 2.6 will occur on Sept. 1 that is intended to "discourage PGP users in the U.S. from using [the previous version] PGP 2.3a, which potentially infringes patents," according to the information document. RSA Data Security Inc., the company which supplies the RSAREF Cryptographic Toolkit used in the PGP Version 2.6 software, would not support the new PGP without the format change, according to the document.

The change makes the new version unable to completely inter-operate with the old, potentially patent-infringing version, according to the document.

After Sept. 1, PGP will produce a slightly different data format. The program will still be able to read and process messages, signatures, and keys produced under the old format, but it will produce data using the new format, according to the PGP manual.

The potential patent infringements of the older PGP 2.3a only applies to the United States. "PGP users [outside the U.S.] are free to use implementations of PGP that do not rely on [the] RSAREF [Cryptographic Toolkit] or its restrictions," according to the PGP Version 2.6 manual.

Although these users are not obligated to upgrade to the newer version, the authors of PGP "are asking them to undergo the inconvenience of making a change to the non-U.S. version of PGP for no technical reason," according to the information document.

The voluntary upgrade "will benefit PGP users outside the U.S. as well as within the U.S.," the document said.

Because of U.S. export controls, the new version cannot be sent outside the country. Instead, the changes necessary to upgrade the old version of PGP have been published by MIT so that users outside of the United States can update the program without exporting the software, according to the document.