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Section 101 Examples
Example 41: Cryptographic Communications

This is an example provided by the U.S. Patent and Trademark Office for analyzing Section 101 patent subject matter eligibility issues. In particular, this example was created to help explain the 2019 Revised Patent Subject Matter Eligibility Guidance (2019 PEG). The original PDF document is found here.

This example should be viewed in light of the introduction that was provided with it.

Index to USPTO's Section 101 Examples
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Example 41: Cryptographic Communications

Background

Security of information is of increasing importance in computer technology. It is critical that data being sent from a sender to a recipient is unable to be intercepted and understood by an intermediate source. In addition, authentication of the source of the message must be ensured along with the verification of and security of the message content. Various cryptographic encoding and decoding methods are available to assist with these security and authentication needs. However, many of them require expensive encoding and decoding hardware as well as a secure way of sharing the private key used to encrypt and decrypt the message. There is a need to perform these same security and authentication functions efficiently over a public key system so that information can be shared easily between users who do not know each other and have not shared the key used to encrypt and decrypt the information.

To solve these problems, applicants have invented a method for establishing cryptographic communications using an algorithm to encrypt a plaintext into a ciphertext. The invention includes at least one encoding device and at least one decoding device, which are computer terminals, and a communication channel, where the encoding and decoding devices are coupled to the communication channel. The encoding device is responsive to a precoded message-to-be-transmitted M and an encoding key E to provide a ciphertext word C for transmission to a particular decoding device. The message-to-be-transmitted is precoded by converting it to a numerical representation which is broken into one or more blocks MA of equal length. This precoding may be done by any conventional means. The resulting message MA is a number representative of a message-to-be-transmitted, where 0 ≤ MA ≤ n-1, where n is a composite number of the form n=p*q, where p and q are prime numbers. The encoding key E is a pair of positive integers e and n, which are related to the particular decoding device. The encoding device distinctly encodes each of the n possible messages. The transformation provided by the encoding device is described by the relation CA=MAe (mod n) where e is a number relatively prime to (p-1)*(q-1). The encoding device transmits the ciphertext word signal CA to the decoding device over the communications channel. The decoding device is responsive to the received ciphertext word CA and a decoding key to transform the ciphertext to a received message word MA’.

The invention improves upon prior methods for establishing cryptographic communications because by using only the variables n and e (which are publicly known), a plaintext can be encrypted by anyone. The variables p and q are only known by the owner of the decryption key d and are used to generate the decryption key (private key d is not claimed below). Thus, the security of the cipher relies on the difficulty of factoring large integers by computers, and there is no known efficient algorithm to recover the plaintext given the ciphertext and the public information (n, e) (assuming that p and q are sufficiently large).

Claim:

A method for establishing cryptographic communications between a first computer terminal and a second computer terminal comprising:
• receiving a plaintext word signal at the first computer terminal;
• transforming the plaintext word signal to one or more message block word signals MA;
• encoding each of the message block word signals MA to produce a ciphertext word signal CA, whereby CA=MAe (mod n);
• where CA is a number representative of an encoded form of message word MA;
• where MA corresponds to a number representative of a message and 0 ≤ MA ≤ n-1;
• where n is a composite number of the form n=p*q; where p and q are prime numbers;
• where e is a number relatively prime to (p-1)*(q-1); and
transmitting the ciphertext word signal CA to the second computer terminal over a communication channel.
Step Analysis
1: Statutory Category? Yes. The claim recites a series of steps and, therefore, is a process.
2A - Prong 1: Judicial Exception Recited? Yes. The claim recites a mathematical formula or calculation that is used to encode each of the message block word signals MA to produce a ciphertext word signal CA, whereby CA=MAe (mod n). Thus, the claim recites a mathematical concept. Note that, in this example, the “encoding” step is determined to recite a mathematical concept because the claim explicitly recites a mathematical formula or calculation.
2A - Prong 2: Integrated into a Practical Application? Yes. The combination of additional elements in the claim (receiving the plaintext word signal at the first computer terminal, transforming the plaintext word signal to one or message block word signals MA, and transmitting the encoded ciphertext word signal CA to the second computer terminal over a communication channel) integrates the exception into a practical application. In particular, the combination of additional elements use the mathematical formulas and calculations in a specific manner that sufficiently limits the use of the mathematical concepts to the practical application of transmitting the ciphertext word signal to a computer terminal over a communication channel. Thus, the mathematical concepts are integrated into a process that secures private network communications, so that a ciphertext word signal can be transmitted between computers of people who do not know each other or who have not shared a private key between them in advance of the message being transmitted, where the security of the cipher relies on the difficulty of factoring large integers by computers. Thus, the claim is not directed to the recited judicial exception, and the claim is eligible. Note that well-understood, routine, conventional subject matter can integrate an abstract idea into a practical application. Thus, even though receiving a signal at a first computer, transforming it and transmitting the transformed signal to a second computer are described in the background as being conventional, Step 2A – Prong 2 does not evaluate whether the additional elements are conventional to determine whether the abstract idea is integrated into a practical application.
2B: Claim provides an Inventive Concept? N/A.