A blockchain is a decentralised ledger that records information of currency transactions distributed across multiple servers. The transactions are added to a database called a block. At the end of a given time period, the block is encrypted using a hashing function. Hashing Function produces a unique number that can be used to represent the data exactly.
A blockchain enables creating new business models. Public blockchains have immutable records and security of transactions. Blockchain users need to secure their private key. The private key prevents hackers from breaking their digital signatures. To prevent malicious transactions, blockchains have consensus algorithms. Consensus algorithms impose validation requirements for transactions. No transaction will get into the ledger without validation. The consensus algorithms prevent tampering of any past transaction. Blockchain security will be at risk when quantum computers emerge. Functioning cryptographic systems such as DES, Triple DES, AES, RSA, Merkle hash-tree signatures, Merkle–Hellman knapsack encryption, Buchmann–Williams class-group encryption, ECDSA, HFEv−, etc are going to break with a quantum computer.
Keywords: Post Quantum Cryptography, Quantum Resistant Blockchain, Cryptography, BlockChain
Block Chain Platforms
Blockchain platforms are of public, private and federated types. Checking for permission (public or private), permissionless and restricted permissions is the difference in the types. A smart contract model of blockchain with roles like Contract Owner, Team Member, Advisor, Holder and interfaces to Asset Proxies, Exchanges, BMC Token, and Asset Tokens. A smart contract implements an interface between the platform Wallet with income and external addresses such as exchanges. Tokens are implemented as token-as-a-currency instruments. They receive proceeds from continuous contributors. The tokens are connected to the platform through the platform asset and proxy asset interfaces. The smart contract for asset token consists of the investment vehicle structure, fees, and assets.
Post Quantum Signature Chains
Naor Yung signature chains are related to signing a message which will have a hash of the public key to sign the next signature. This creates a chain of related messages. The public key of the chain’s first node is used as a long term public key to create a hash address. Verifying a long term public key is to check if it belongs to the corresponding signature chain. It is tough to change previously created signatures as chaining provide forward security to signature schemes.
The chain is forked by signing n new public key hashes instead of one. This results in a tree of signatures so that a previous fork can be used in case current chain is broken. Verification of signature happens when signed public key hashes are sent along with it. The signature of a long term address σlt as a tuple of one-time signature and a number of public key hashes.
σlt = (σots,pkh0,…,pkhb−1)
The entire chain of signatures needs to be stored so that every previous link in the signature chain can be looked up. Many algorithms rely on signature chains which have key generation, signing and verification algorithms.
QUANTUM RESISTANT BLOCKCHAIN
A blockchain is a ledger that records information related to transactions. The transactions are continually added by block size. At the end of a given time period, the block is encrypted using a hashing function. Public permission-less blockchain networks allow disruption of centralized player. Public blockchains ensure immutable records and security of transactions. Quantum computers can break the hash signatures using Shor’s algorithm. There is a need for a post-quantum secure signature scheme for post-quantum blockchain security.
The Quantum Resistant ledger is a cryptocurrency that strives to remain on the bleeding edge of security and functionality. It features quantum resistant cryptographic protocols and a custom proof of stake system. The cryptocurrency ledger is resistant to both classical and quantum computing attack. It uses hash-based digital signatures which are quantum-resistant. The ledger provides an ultra-secure backup store of value in the event of a sudden advance in quantum computing. The initial aim of the chain is to offer a low volume of ultra-secure transactions in the first iteration with guaranteed longevity.
Quantum resistant hashtag based signature tree like Extended Merkel signature scheme and a low power proof of stake algorithm is used for quantum resistant ledgers. Extended Merkel signature uses a one-time signature scheme. This scheme signs one message with one key. One Time Signature (OTS) key is used to sign two different messages so that an attacker could generate a valid signature for a third message you had never signed before. An attacker can generate a valid transaction which is never approved. One can use a different OTS key for each message.
A quantum secure signature scheme combined with a hash-based signature scheme with Naor Yung chaining secures a blockchain. Extended Naor Yung Signature scheme has algorithms for key generation, signing, and verification of blockchain transaction blocks. The entire chain is stored in the blockchain and look up for finding one with root public keys is easy. Hash chains suffer from the limitation related to having a finite number of links which when exhausted requires the system to be re-initialized. Conventional Hash chain needs to be replaced by Re-initializable Hash Chain. The re-initializable hash chain has the property that if its links are exhausted. It can be securely re-initialized in a non-repudiable manner to result in another hash chain. This process can be continued indefinitely to give rise to an infinite length hash chain. Thus an infinite number of finite length hash chains tied together.
Post Quantum cryptography is catching up and four types of cryptosystems elliptic curves, lattices, isogenies, and hash-based signatures are grabbing attention in academia and NIST. McEliece with Goppa codes is the reliable cryptosystem. Using a Shor’s algorithm variant, quantum computer underpins the security of blockchain. Quantum cryptographic codes can secure block chains and the transactions. Quantum key distribution with post-quantum cryptography helps in securing blockchain. Blockchain communities are proactively looking to come up with innovative techniques to tackle quantum computing process power.
- NIST Post Quantum Cryptography Project
- Block Chain Research Institute Quantum Proofing Block Chain
- European Telecommunications Standards Institute Quantum Safe Cryptography
Quantum Resistant Blockchain was originally published in Data Driven Investor on Medium, where people are continuing the conversation by highlighting and responding to this story.