Method and system for securing post-quantum blockchains
View Patent ↗A system and method are provided for transitioning a distributed ledger or blockchain to a post-quantum authorization through a soft fork that avoids interruption or delay of network operation including defining a first activation block height (h 1 ) to initiate the transition and a second activation block height (h 2 ) greater than the first activation block height to complete the transition. For each block during the transition, transactions are validated by applying a height-based rule set that enforces a classical digital signature scheme before the first activation block height, permits both classical and post-quantum digital signature schemes between the first and second activation heights while requiring post-quantum authorization for newly created ledger units and enforces only post-quantum authorization after the second activation height. At the second activation height, all ledger units authorized under the classical digital signature scheme become invalid, resulting in a distributed ledger operating exclusively under post-quantum authorization.
1 . A method for transitioning a distributed ledger to a post-quantum authorization, comprising:
defining a first activation block height (h 1 ) to initiate a soft fork and a second activation block height (h 2 ) greater than the first activation block height;
validating, for each block (b) at a block height H, each transaction in the block (b) by applying a height-based rule set that comprises:
validating, when H<h 1 , that each input ledger unit referenced by the transaction is authorized under a classical digital signature scheme;
validating, when h 1 ≤H≤h 2 , that each input ledger unit referenced by the transaction is authorized under either the classical digital signature scheme or a post-quantum digital signature scheme and validating that each output ledger unit created by the transaction is authorized under the post-quantum digital signature scheme; and
validating, when H>h 2 , that each input ledger unit referenced by the transaction is authorized under the post-quantum digital signature scheme; and
committing the block (b) to the distributed ledger when each transaction in the block (b) satisfies the height-based rule set or rejecting the block (b) otherwise.
2 . The method of claim 1 , wherein each ledger unit, including an input ledger unit and an output ledger unit, comprises a blockchain-tracked unit including a digital coin or an application token.
3 . The method of claim 1 , further comprising verifying, for each input ledger unit of each transaction, that the input ledger unit is unspent on the distributed ledger before treating the transaction as valid.
4 . The method of claim 1 , further comprising determining whether a ledger unit is authorized under the classical digital signature scheme or the post-quantum digital signature scheme based on the block height at which the ledger unit was created relative to the first activation block height (h 1 ).
5 . The method of claim 1 , further comprising:
treating each unspent ledger unit authorized under the classical digital signature scheme as expired at block height h 2 ; and
rejecting each transaction that references an expired ledger unit as an input after block height h 2 .
6 . The method of claim 5 , further comprising adjusting a block reward after block height h 2 by an amount corresponding to the expired ledger units authorized under the classical digital signature scheme.
7 . The method of claim 1 , further comprising announcing to a plurality of network peers an expected expiration date for ledger units authorized under the classical digital signature scheme, the expected expiration date being based on an expected date at which block height h 2 is reached.
8 . The method of claim 1 , further comprising converting, during h 1 ≤H≤h 2 , each ledger unit authorized under the classical digital signature scheme into a ledger unit authorized under the post-quantum digital signature scheme by initiating a self-transfer to a post-quantum address.
9 . The method of claim 1 , wherein the post-quantum digital signature scheme comprises one of a hash-based scheme, a lattice-based scheme, a code-based scheme, a multivariate scheme, and an isogeny-based scheme.
10 . The method of claim 1 , further comprising tracking non-currency application tokens and applying the height-based rule set to state updates representing at least one of supply-chain provenance, smart-contract state, e-government services, digital-identity credentials and healthcare records.
11 . A system for transitioning a distributed ledger to post-quantum authorization, comprising one or more processors and a memory storing instructions that, when executed by the one or more processors, cause the system to:
define a first activation block height (h 1 ) to initiate a soft fork and a second activation block height (h 2 ) greater than the first activation block height;
validate, for each block (b) at a block height H, each transaction in the block (b) by applying a height-based rule set that comprises:
validating, when H<h 1 , that each input ledger unit referenced by the transaction is authorized under a classical digital signature scheme;
validating, when h 1 ≤H≤h 2 , that each input ledger unit referenced by the transaction is authorized under either the classical digital signature scheme or a post-quantum digital signature scheme and validating that each output ledger unit created by the transaction is authorized under the post-quantum digital signature scheme; and
validating, when H>h 2 , that each input ledger unit referenced by the transaction is authorized under the post-quantum digital signature scheme; and
commit the block (b) to the distributed ledger when each transaction in the block (b) satisfies the height-based rule set or reject the block (b) otherwise.
12 . The system of claim 11 , wherein each ledger unit including an input ledger unit and an output ledger unit comprises a blockchain-tracked unit including a digital coin or an application token.
13 . The system of claim 11 , wherein the one or more processors are further configured to verify, for each input ledger unit of each transaction, that the input ledger unit is unspent on the distributed ledger before treating the transaction as valid.
14 . The system of claim 11 , wherein the one or more processors are further configured to determine whether a ledger unit is authorized under the classical digital signature scheme or the post-quantum digital signature scheme based on the block height at which the ledger unit was created relative to the first activation block height (h 1 ).
15 . The system of claim 11 , wherein the one or more processors are further configured to:
treat each unspent ledger unit authorized under the classical digital signature scheme as expired at block height h 2 ; and
reject each transaction that references an expired ledger unit as an input after block height h 2 .
16 . The system of claim 15 , wherein the one or more processors are further configured to adjust a block reward after block height h 2 by an amount corresponding to the expired ledger units authorized under the classical digital signature scheme.
17 . The system of claim 11 , wherein the one or more processors are further configured to announce to a plurality of network peers an expected expiration date for ledger units authorized under the classical digital signature scheme, the expected expiration date being based on an expected date at which block height h 2 is reached.
18 . The system of claim 11 , wherein the one or more processors are further configured to convert, during h 1 ≤H≤h 2 , each ledger unit authorized under the classical digital signature scheme into a ledger unit authorized under the post-quantum digital signature scheme by initiating a self-transfer to a post-quantum address.
19 . The system of claim 11 , wherein the post-quantum digital signature scheme comprises one of a hash-based scheme, a lattice-based scheme, a code-based scheme, a multivariate scheme, and an isogeny-based scheme.
20 . The system of claim 11 , wherein the one or more processors are further configured to track non-currency application tokens and apply the height-based rule set to state updates representing at least one of supply-chain provenance, smart-contract state, e-government services, digital-identity credentials, and healthcare records.