Patents and Standards

Contents in Brief

  • 15.1 Introduction.............................635
  • 15.2 Patents on cryptographic techniques................635
  • 15.3 Cryptographic standards......................645
  • 15.4 Notes and further references....................657


This chapter discusses two topics which have significant impact on the use of cryptography in practice: patents and standards. At their best, cryptographic patents make details of significant new processes and efficient techniques publicly available, thereby increasing awareness and promoting use; at their worst, they limit or stifle the use of such techniques due to licensing requirements. Cryptographic standards serve two important goals: facilitating widespread use of cryptographically sound and well-accepted techniques; and promoting interoperability between components involving security mechanisms in various systems.

An overview of patents is given in §15.2. Standards are pursued in §15.3. Notes and further references follow in §15.4.

Patents on cryptographic techniques

A vast number of cryptographic patents have been issued, of widely varying significance and use. Here attention is focused on a subset of these with primary emphasis on unexpired patents of industrial interest, involving fundamental techniques and specific algorithms and protocols. In addition, some patents of historical interest are noted.

Where appropriate, a brief description of major claims or disclosed techniques is given. Inclusion herein is intended to provide reference information to practitioners on the existence and content of well-known patents, and to illustrate the nature of cryptographic patents in general. There is no intention to convey any judgement on the validity of any claims.

Because most patents are eventually filed in the United States, U.S. patent numbers and associated details are given. Additional information including related filings in other countries may be found in patent databases. For further technical details, the original patents should be consulted (see §15.2.4). Where details of patented techniques and algorithms appear elsewhere in this book, cross-references are given.

Expiry of patents

U.S. patents are valid for 17 years from the date of issue, or 20 years from the date a patent application was filed. For applications filed before June 8 1995 (and unexpired at that point), the longer period applies; the 20-year rule applies for applications filed after this date.

Priority data

Many countries require that a patent be filed before any public disclosure of the invention; in the USA, the fifing must be within one year of disclosure. A large number of countries are parties to a patent agreement which recognizes priority dates. A patent filed in such a country, and filed in another such country within one year thereof, may claim the date of the first filing as a priority date for the later filing.

Outline of patents section

The discussion of patents is broken into three main subsections. §15.2.1 notes five fundamental patents, including DES and basic patents on public-key cryptography. §15.2.2 addresses ten prominent patents including those on well-known block ciphers, hash functions, identification and signature schemes. §15.2.3 includes ten additional patents addressing various techniques, of historical or practical interest. Finally, §15.2.4 provides information on ordering patents.

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