Computer-implemented systems and methods for authorising blockchain transactions with low-entropy passwords

Patent metadata

Field	Value
Publication number	US-11429956-B2
Application number	US-201816954173-A
Country	US
Kind code	B2
Filing date	Dec 12, 2018
Priority date	Dec 15, 2017
Publication date	Aug 30, 2022
Grant date	Aug 30, 2022

Abstract

There may be provided a blockchain-implemented security method involving a requestor and a group of nodes, which includes generating a cryptographic key of the requestor based on a password chosen by the requestor and first quantities sent by the group of nodes (which are derived from private key shares of the group of nodes and a generator function of a digital signature scheme employing a bilinear mapping on an elliptic curve). A cryptographic signature for a requestor blockchain transaction can be generated where the signature corresponds to the requestor's cryptographic key. The signature can be based on the password and second quantities sent by the group of nodes (which are also derived from the group private key shares). The method can further include verifying the cryptographic signature of the blockchain transaction using the requestor's cryptographic key. Additionally or alternatively, the method can employ a consensus mechanism involving the group of nodes to allow the requestor to authorise a transaction with a password. The method can be logically partitioned into a sequence of phases, including an initialisation phase, a funding phase, and a payment authorization phase (which involves a pre-spending transaction and a spending transaction).

First claim

The invention claimed is:

1. A blockchain-implemented security method involving a requestor and a group of nodes, the blockchain-implemented security method comprising:
establishing the group of nodes operably coupled to one another via at least one communication network, wherein each node of the group transfers a digital asset to the group, and wherein each node of the group stores a corresponding private key share;
broadcasting, by a requestor system, an initialisation transaction from the requestor for communication to the group, wherein the initialisation transaction indicates a desire to set a password associated with the requestor;
generating, by the nodes of the group, a plurality of first quantities in response to the initialisation transaction, wherein a first quantity generated by a first node is based at least in part on a first private key share of the first node and a generator function of a digital signature scheme employing a bilinear mapping on an elliptic curve;
sending, by the nodes of the group, respective first messages to the requestor, wherein the respective first messages include the plurality of first quantities;
generating, by the requestor system, a cryptographic key based on a password chosen by the requestor and the plurality of first quantities;
broadcasting, by the requestor system, a funding transaction from the requestor for communication to the group, wherein the funding transaction specifies one or more digital assets of the requestor, further wherein all or some of such digital assets are transferrable using the password chosen by the requestor and include the cryptographic key;
broadcasting, by the requestor system, a pre-spending transaction from the requestor for communication to the group, wherein the pre-spending transaction is unsigned, transfers a transaction deposit, and includes a hash of the pre-spending transaction that transfers a portion of funds of the one or more digital assets of the requestor using a hash function of the digital signature scheme;
generating, by the nodes of the group, a plurality of second quantities in response to the pre-spending transaction, wherein a second quantity generated by a second node is based at least in part on the hash of the pre-spending transaction as included in the pre-spending transaction and a second private key share of the second node;
sending, by the nodes of the group, respective second messages to the requestor, wherein the respective second messages include the plurality of second quantities;
generating, by the requestor system, a cryptographic signature based on the password chosen by the requestor and the plurality of second quantities, wherein the cryptographic signature corresponds to the cryptographic key of the requestor based on the bilinear mapping on the elliptic curve of the digital signature scheme;
broadcasting, by the requestor system, a spending transaction from the requestor for communication to the group, wherein the spending transaction transfers the portion of funds of the one or more digital assets of the requestor, and wherein the spending transaction is based on an unsigned spending transaction and is signed with the cryptographic signature; and
verifying, by at least the nodes of the group, the cryptographic signature of the spending transaction using the cryptographic key of the requestor in the funding transaction,
wherein, based on the verification, the spending transaction is stored in the blockchain, confirming a transfer of the portion of funds of the requestor to a recipient of the spending transaction.

2. The blockchain-implemented security method according to claim 1 , further comprising:
receiving, by the nodes of the group, the funding transaction from the requestor; and
receiving, by the nodes of the group, the spending transaction from the requestor.

3. The blockchain-implemented security method according to claim 2 , further comprising:
receiving, by the nodes of the group, the initialisation transaction from the requestor.

4. The blockchain-implemented security method according to claim 2 , further comprising:
receiving, by the nodes of the group, the pre-spending transaction from the requestor.

5. The blockchain-implemented security method according to claim 3 , wherein:
the initialisation transaction includes an initialisation fee that is at least one of:
paid by the requestor to the group;
paid to a public group address associated with the group; and/or
returned to the requestor in the event that at least one node of the group sends an inconsistent first quantity to the requestor, wherein the inconsistent first quantity is determined using a verifiable secret sharing scheme.

6. The blockchain-implemented security method according to claim 4 , wherein:
the pre-spending transaction further defines a spending fee; and/or
the transaction deposit is locked under a public group address associated with the group; and/or
the group selectively transfers the transaction deposit less the spending fee back to the requestor in the event that the verifying is successful; and/or
the group selectively confiscates the transaction deposit in the event that the verifying fails; and/or
the transaction deposit is returned to the requestor in the event that at least one node of the group of nodes sends an inconsistent second quantity to the requestor, wherein the inconsistent second quantity is determined using a verifiable secret sharing scheme; and/or
the spending fee is paid to a public group address associated with the group; and/or
the nodes of the group verify that the spending fee is sufficient, wherein sufficiency of the spending fee is based on computation resources required to process a third transaction and the spending transaction; and/or
the nodes of the group selectively bypass further processing of the pre-spending transaction in the event of failed verification of sufficiency of the spending fee; and/or
the group selectively distributes the spending fee to the group in the event of successful verification of the cryptographic signature of the spending transaction.

7. The blockchain-implemented security method according to claim 1 .

8. The blockchain-implemented security method according to claim 2 , wherein:
the funding transaction specifies that the one or more digital assets of the requestor are locked by the cryptographic key and thus can be spent by the cryptographic signature; and
the verifying of the cryptographic signature of the spending transaction is performed by the group and optionally by other nodes that do not belong to the group.

9. The blockchain-implemented security method according to claim 2 , wherein:
the funding transaction specifies that the one or more digital assets of the requestor are locked by a public key of the group and thus can be spent by a signature based on a threshold number of private key shares of the group;
the verifying of the cryptographic signature of the spending transaction is performed only by the group; and
upon successful verification of the cryptographic signature of the spending transaction, the group cooperates to generate the signature based on the threshold number of private key shares of the group and to construct a secondary spending transaction that includes the signature.

10. The blockchain-implemented security method according to claim 2 , wherein:
the plurality of first quantities are included in private messages sent from the nodes of the group to the requestor and/or are encrypted with a public key of the requestor; and/or
the nodes of the group each have a trusted execution environment that stores the corresponding private key share of the node; and/or
the trusted execution enviro

Assignees

• Nchain Holdings Ltd

Inventors

• Bartolucci Silvia
• Fletcher John

Classifications

• G06Q20/389

  Keeping log of transactions for guaranteeing non-repudiation of a transaction · CPC title

• G06F21/64 Primary

  Protecting data integrity, e.g. using checksums, certificates or signatures · CPC title

• H04L9/50

  using hash chains, e.g. blockchains or hash trees · CPC title

• H04L9/3247

  involving digital signatures · CPC title

• H04L9/3239 Primary

  involving non-keyed hash functions, e.g. modification detection codes [MDCs], MD5, SHA or RIPEMD · CPC title