# US 10,320,758 B2 · Cryptography using multi-factor key system and finite state machine > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,320,758 B2 - Document ID: US10320758B2 - Status: Granted - Kind: B2 - Application number: 15/496,020 - Filed: 2017-04-25 - Published: 2018-10-25 - Granted: 2019-06-11 - Earliest claimed: 2017-04-25 - Assignees: International Business Machines Corporation - Applicants: International Business Machines Corporation - Inventors: Samuel M. Jawaharlal; Arunachalam Narayanan; Sathya Santhar; Balamurugaramanathan Sivaramalingam - Web page: https://patentgrep.com/patent/US10320758B2 ## CPC - H04L 63/0442: {wherein the sending and receiving network entities apply asymmetric encryption, i.e. different keys for encryption and decryption (cryptographic mechanisms or cryptographic arrangements for public-key encryption H04L9/30)} - H04L 9/14: using a plurality of keys or algorithms - H04L 9/30: Public key, i.e. encryption algorithm being computationally infeasible to invert or user's encryption keys not requiring secrecy - H04L 9/3006: {underlying computational problems or public-key parameters} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A process selects a public key from a plurality of public keys provided by a message recipient that is to receive an encrypted message. The process establishes an input alphabet for a finite-state machine. The process further constructs the finite-state machine and a language over the input alphabet such that the finite-state machine accepts the language, where the language includes language elements. The process encrypts a language element of the language using the selected public key to provide an encrypted language element. The process electronically transmits the encrypted language element and a specification of the finite-state machine to the message recipient for securely identifying the selected public key to the message recipient. The process encrypts a message using the selected public key to provide the encrypted message. The process also electronically transmits the encrypted message to the message recipient. ## Claims ### Claim 1 A computer-implemented method comprising: selecting, by a first computing device, a public key from a plurality of public keys provided by a message recipient that is to receive an encrypted message over a communication network; establishing an input alphabet for a finite-state machine; constructing the finite-state machine and a language over the input alphabet such that the finite-state machine accepts the language, wherein the language comprises language elements; encrypting a language element of the language using the selected public key to provide an encrypted language element; electronically transmitting the encrypted language element and a specification of the finite-state machine to the message recipient for securely identifying the selected public key to the message recipient, wherein the message recipient comprises a second computing device; encrypting a message using the selected public key to provide the encrypted message to the first computing device; and electronically transmitting the encrypted message to the message recipient. ### Claim 2 (depends on 1) The method of claim 1, wherein the language is a regular language and the finite-state machine accepts only the elements of the language. ### Claim 3 (depends on 1) The method of claim 1, further comprising randomly selecting the language element from the plurality of language elements of the language. ### Claim 4 (depends on 1) The method of claim 1, wherein the electronically transmitting the encrypted message to the message recipient is based on receiving an indication from the message recipient that electronic transmission of the encrypted message is to commence. ### Claim 5 (depends on 4) The method of claim 4, wherein the receiving the indication from the message recipient is based on the message recipient identifying the selected public key from the plurality of public keys and identifying a private key corresponding to the selected public key. ### Claim 6 (depends on 1) The method of claim 1, further comprising performing an initial attempt to securely identify an initial public key of the plurality of public keys to the message recipient, wherein based on an initial constructed finite-state machine and initial encrypted language element, decryption of the initial encrypted language element using each private key of a plurality of private keys corresponding to the plurality of public keys provides a plurality of initial decrypted language elements that are accepted by the initial finite-state machine, thereby indicating multiple candidate public keys, of the plurality of public keys, that could be the initial public key. ### Claim 7 (depends on 6) The method of claim 6, wherein based on receiving an indication from the message recipient that a definitive identification of the initial public key to the message recipient has failed, the method performs the selecting the public key, the establishing the input alphabet, and the constructing the finite-state machine and language over the input alphabet. ### Claim 8 (depends on 1) The method of claim 1, further comprising initially determining whether to encrypt the message using a first encryption technique including a single cryptographic key pair or using a second encryption technique, the second encryption technique comprising the selecting the public key, the establishing the input alphabet, the constructing the finite-state machine and language over the input alphabet, the encrypting the language element, and the electronically transmitting the encrypted language element and specification of the finite-state machine to the message recipient. ### Claim 9 (depends on 8) The method of claim 8, wherein the determining whether to use the first encryption technique or the second encryption technique is based on weighing an anticipated length of data transfer of the encrypted message against resource consumption anticipated to be consumed in identifying, for the message recipient a public key, of the plurality of public keys, to be used to encrypt the message. ### Claim 10 A computer program product comprising: a non-transitory computer readable storage medium readable by a processor and storing instructions for execution by the processor for performing a method comprising: selecting, by a first computing device, a public key from a plurality of public keys provided by a message recipient that is to receive an encrypted message over a communication network; establishing an input alphabet for a finite-state machine; constructing the finite-state machine and a language over the input alphabet such that the finite-state machine accepts the language, wherein the language comprises language elements; encrypting a language element of the language using the selected public key to provide an encrypted language element; electronically transmitting the encrypted language element and a specification of the finite-state machine to the message recipient for securely identifying the selected public key to the message recipient, wherein the message recipient comprises a second computing device; encrypting a message using the selected public key to provide the encrypted message to the first computing device; and electronically transmitting the encrypted message to the message recipient. ### Claim 11 (depends on 10) The computer program product of claim 10, wherein the language is a regular language and the finite-state machine accepts only the elements of the language. ### Claim 12 (depends on 10) The computer program product of claim 10, wherein the electronically transmitting the encrypted message to the message recipient is based on receiving an indication from the message recipient that electronic transmission of the encrypted message is to commence. ### Claim 13 (depends on 12) The computer program product of claim 12, wherein the receiving the indication from the message recipient is based on the message recipient identifying the selected public key from the plurality of public keys and identifying a private key corresponding to the selected public key. ### Claim 14 (depends on 10) The computer program product of claim 10, wherein the method further comprises initially determining whether to encrypt the message using a first encryption technique including a single cryptographic key pair or using a second encryption technique, the second encryption technique comprising the selecting the public key, the establishing the input alphabet, the constructing the finite-state machine and language over the input alphabet, the encrypting the language element, and the electronically transmitting the encrypted language element and specification of the finite-state machine to the message recipient. ### Claim 15 (depends on 14) The computer program product of claim 14, wherein the determining whether to use the first encryption technique or the second encryption technique is based on weighing an anticipated length of data transfer of the encrypted message against resource consumption anticipated to be consumed in identifying, for the message recipient a public key, of the plurality of public keys, to be used to encrypt the message. ### Claim 16 A computer system comprising: a memory device; and a hardware processor in communications with the memory, wherein the computer system is configured to perform a method comprising: selecting, by a first computer system, a public key from a plurality of public keys provided by a message recipient that is to receive an encrypted message over a communication network; establishing an input alphabet for a finite-state machine; constructing the finite-state machine and a language over the input alphabet such that the finite-state machine accepts the language, wherein the language comprises language elements; encrypting a language element of the language using the selected public key to provide an encrypted language element; electronically transmitting the encrypted language element and a specification of the finite-state machine to the message recipient for securely identifying the selected public key to the message recipient, wherein the message recipient comprises a second computer device; encrypting a message using the selected public key to provide the encrypted message to the first computing device; and electronically transmitting the encrypted message to the message recipient. ### Claim 17 (depends on 16) The computer system of claim 16, wherein the language is a regular language and the finite-state machine accepts only the elements of the language. ### Claim 18 (depends on 16) The computer system of claim 16, wherein the electronically transmitting the encrypted message to the message recipient is based on receiving an indication from the message recipient that electronic transmission of the encrypted message is to commence. ### Claim 19 (depends on 18) The computer system of claim 18, wherein the receiving the indication from the message recipient is based on the message recipient identifying the selected public key from the plurality of public keys and identifying a private key corresponding to the selected public key. ### Claim 20 (depends on 16) The computer system of claim 16, wherein the method further comprises initially determining whether to encrypt the message using a first encryption technique including a single cryptographic key pair or using a second encryption technique, the second encryption technique comprising the selecting the public key, the establishing the input alphabet, the constructing the finite-state machine and language over the input alphabet, the encrypting the language element, and the electronically transmitting the encrypted language element and specification of the finite-state machine to the message recipient, and wherein the determining whether to use the first encryption technique or the second encryption technique is based on weighing an anticipated length of data transfer of the encrypted message against resource consumption anticipated to be consumed in identifying, for the message recipient a public key, of the plurality of public keys, to be used to encrypt the message.