# US 12,120,223 B2 · Scalable security for cryptographic ledgers via dynamic and unpredictable changes to quorum memberships > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,120,223 B2 - Document ID: US12120223B2 - Status: Granted - Kind: B2 - Application number: 18/346,513 - Filed: 2023-07-03 - Published: 2024-02-08 - Granted: 2024-10-15 - Earliest claimed: 2019-03-13 - Assignees: Google Inc. - Applicants: Google LLC - Inventors: William Douglas Cox; Bo Zhu; Orest Bolohan; Sheldon I. Walfish - Web page: https://patentgrep.com/patent/US12120223B2 ## CPC - H04L 9/085: {Secret sharing or secret splitting, e.g. threshold schemes} - H04L 9/3239: {involving non-keyed hash functions, e.g. modification detection codes [MDCs], MD5, SHA or RIPEMD} - H04L 9/0637: {Modes of operation, e.g. cipher block chaining [CBC], electronic codebook [ECB] or Galois/counter mode [GCM]} - H04L 9/0643: {Hash functions, e.g. MD5, SHA, HMAC or f9 MAC} - H04L 9/30: Public key, i.e. encryption algorithm being computationally infeasible to invert or user's encryption keys not requiring secrecy - H04L 9/3255: {using group based signatures, e.g. ring or threshold signatures} - H04L 9/50: {using hash chains, e.g. blockchains or hash trees} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract The present disclosure provides computing systems in which respective quorums of computing nodes securely manage respective secrets associated with cryptographic ledgers according to threshold secret sharing schemes. In particular, membership in the quorums can be changed dynamically and unpredictability to improve security of the quorums against adversarial attacks in which adversaries attempt to compromise or gain control of the computing nodes. More specifically, by changing membership in the quorum dynamically and unpredictability, the ability of the adversary to control at any given time a threshold number of the current members of the quorum and gain access to the secret is dramatically reduced. ## Claims ### Claim 1 A computing system comprising: one or more processors; and one or more non-transitory computer-readable media storing instructions that are executable to perform operations, the operations comprising: storing, by one or more master computing nodes of a master quorum, a master secret according to a threshold secret sharing scheme, wherein the master quorum is configured to use the master secret to control changes in a respective membership of each of a plurality of subordinate quorums that are respectively associated with a plurality of cryptographic ledgers, wherein the respective membership of each subordinate quorum comprises a dynamically changing plurality of subordinate computing nodes that respectively store respective shares of a respective subordinate secret associated with the respective cryptographic ledger according to the threshold secret sharing scheme; periodically receiving, by the master quorum, a quorum-signed proof of liveness from each subordinate quorum; and providing, by the master quorum, responsive to receipt of the quorum-signed proof of liveness from at least one subordinate quorum of the subordinate quorums, a certificate of operation to the at least one subordinate quorum, wherein the certificate of operation specifies a period of time for which the subordinate quorum is approved to operate, and wherein each subordinate computing node is configured to erase its respective share of the respective subordinate secret when its current certificate of operation expires and it has not received a new certificate of operation. ### Claim 2 (depends on 1) The computing system of claim 1, the operations comprising: receiving, by the master quorum, information excluding the proof of liveness from the at least one subordinate quorum; and erasing, by the master quorum, responsive to receiving the information excluding the proof of liveness from the at least one subordinate quorum, the at least one subordinate quorum's respective share of the respective subordinate secret. ### Claim 3 (depends on 1) The computing system of claim 1, wherein the information excluding the proof of liveness from the at least one subordinate quorum comprises the at least one subordinate quorum's certificate of operation expiring and no new certificate of operation being received. ### Claim 4 (depends on 1) The computing system of claim 1, wherein each master computing node stores its respective share of the master secret in a non-temporary memory location that persists against node power failure. ### Claim 5 (depends on 1) The computing system of claim 1, wherein each subordinate computing node stores its respective share of the subordinate secret in a temporary memory location that does not persist against node power failure. ### Claim 6 (depends on 1) The computing system of any claim 1, wherein the master quorum is configured to vote to start or re-start a given subordinate quorum. ### Claim 7 (depends on 1) The computing system of claim 1, wherein the master quorum is configured to periodically receive a quorum-signed proof of liveness from each subordinate quorum. ### Claim 8 (depends on 5) The computing system of claim 5, wherein, in response to receipt of the quorum-signed proof of liveness from one of the subordinate quorums, the master quorum is configured to provide a certificate of operation to the subordinate quorum, wherein the certificate of operation specifies a period of time for which the subordinate quorum is approved to operate, and wherein each subordinate computing node is configured to erase its respective share of the respective subordinate secret when its current certificate of operation expires and it has not received a new certificate of operation. ### Claim 9 (depends on 5) The computing system of claim 5, wherein the master quorum is configured to: detect when a proof of liveness has not been received from one of the subordinate quorums within a threshold period of time; and in response, re-initialize the subordinate quorum with the membership at least partially modified. ### Claim 10 (depends on 1) The computing system of claim 1, wherein at least one of the one or more cryptographic ledgers comprises a smart contract that controls operations of the respective subordinate quorum. ### Claim 11 (depends on 10) The computing system of claim 10, wherein the smart contract comprises at least one rule that enables control of the subordinate quorum via a backdoor under a condition that each instance of subordinate quorum control undertaken under the at least one rule is irreversibly acknowledged on the cryptographic ledger. ### Claim 12 (depends on 1) The computing system of claim 1, wherein: a master cryptographic ledger is associated with the master quorum; and the master cryptographic ledger stores the respective subordinate secret associated with each cryptographic ledger. ### Claim 13 A method to prevent a subordinate quorum from performing conflicting operations by: obtaining, by a master quorum, from each subordinate member of the subordinate quorum before the subordinate member drops out of the subordinate quorum, a required quorum departure certificate; requiring each subordinate member of the subordinate quorum to record a quorum departure certificate in persistent before dropping out of the subordinate quorum; obtaining, by the master quorum, a request to re-start the subordinate quorum; responsive to obtaining the request to re-start the subordinate quorum, obtaining the required quorum departure certificate from a plurality of subordinate members; determining that a required number of subordinate members of the subordinate quorum have the required departure certificate; and restarting the subordinate quorum responsive determining that the required number of subordinate members of the subordinate quorum have the required departure certificate. ### Claim 14 (depends on 13) The method of claim 13, wherein the required number of subordinate members is a number greater than one third of the total number of subordinate members. ### Claim 15 (depends on 13) The method of claim 13, wherein the quorum departure certificate is associated with a verifiable transaction number. ### Claim 16 (depends on 13) The method of claim 13, wherein the quorum departure certificate with a highest verifiable transaction number comprises data indicative of the subordinate quorum stopping functioning. ### Claim 17 One or more non-transitory computer-readable media storing instructions that are executable to cause one or more processors to perform operations, the operations comprising: storing, by the one or more master computing nodes, a master secret according to a threshold secret sharing scheme, wherein the master quorum is configured to use the master secret to control changes in a respective membership of each of a plurality of subordinate quorums that are respectively associated with a plurality of cryptographic ledgers, wherein the respective membership of each subordinate quorum comprises a dynamically changing plurality of subordinate computing nodes that respectively store respective shares of a respective subordinate secret associated with the respective cryptographic ledger according to the threshold secret sharing scheme; periodically receiving, by the master quorum, a quorum-signed proof of liveness from each subordinate quorum; and providing, by the master quorum, responsive to receipt of the quorum-signed proof of liveness from at least one subordinate quorum of the subordinate quorums, a certificate of operation to the at least one subordinate quorum, wherein the certificate of operation specifies a period of time for which the subordinate quorum is approved to operate, and wherein each subordinate computing node is configured to erase its respective share of the respective subordinate secret when its current certificate of operation expires and it has not received a new certificate of operation. ### Claim 18 (depends on 17) The one or more non-transitory computer-readable media of claim 17, wherein the required number of subordinate members is a number greater than one third of the total number of subordinate members. ### Claim 19 (depends on 17) The one or more non-transitory computer-readable media of claim 17, wherein the quorum departure certificate is associated with a verifiable transaction number. ### Claim 20 (depends on 17) The one or more non-transitory computer-readable media of claim 17, wherein the quorum departure certificate with a highest verifiable transaction number comprises data indicative of the subordinate quorum stopping functioning.