Quantum secured blockchain framework for enhancing post quantum data security

This paper proposes a QuantumShield-BC framework to provide end-to-end protection for blockchain systems in the quantum age. It incorporates post-quantum digital signatures at the protocol layer, quantum key distribution (QKD) at the network layer, and a Quantum Byzantine Fault Tolerance (Q-BFT) consensus mechanism based on quantum random number generation (QRNG) to provide end-to-end quantum attack resistance, scalability, fairness, and high transaction throughput.

Introduction to QuantumShield-BC

One of the challenges it poses for blockchain technology is that quantum computing has a disruptive capability concerning the cryptographic techniques we use, primarily traditional cryptographic methods such as RSA and ECC. However, the main disadvantage of all these classical methods is their vulnerability once large-scale quantum computers become available and can perform quantum attacks, such as Shor’s algorithm, which efficiently breaks widely used public-key encryption schemes. It has led to the need for quantum-resistant blockchain architectures that ensure the security and safety of these decentralized methodologies against any future threats. Abstract: QuantumShield-BC is a quantum-secured blockchain framework that combines post-quantum cryptography (PQC) and quantum key distribution (QKD) to provide real-time security and resilience against quantum attacks over the long term.

The growing reliance on blockchain technologies for secure transactions, digital identity management, and decentralized applications (DApps) further underscores the necessity of quantum-resistant mechanisms as timelines for such attacks get shorter. However, this dependence on classical encryption introduces the risk of vulnerabilities in existing blockchain security models, as classical encryption can be solved in polynomial time with the aid of quantum computers. QuantumShield-BC addresses this issue by utilizing lattice-based post-quantum digital signatures that can be seamlessly integrated into smart contracts, thereby significantly lowering the barrier to usage on existing protocols while ensuring signature security, even in a quantum adversarial setting. Moreover, Quantum Key Distribution (QKD) is implemented by creating a secure peer-to-peer communication channel to prevent eavesdropping and man-in-the-middle attacks.

Deterministic PRNGs pose a significant attack vector for classical blockchains, as they often lead to nonce prediction in digital signatures, which attackers can exploit. QuantumShield-BC further introduces quantum random number generation (QRNG), providing cryptographically secure random values for generating transaction hashes and executing smart contracts, as well as for the consensus mechanism, significantly augmenting entropy and security. This introduces random deviation, thereby strengthening the protection of classical cryptography against more predictable attacks.

In Fig. 1, in addition to securing each transaction, QuantumShield-BC replaces standard proof-of-stake (PoS) and proof-of-work (PoW) models with a Quantum-enhanced Byzantine Fault Tolerance (Q-BFT) consensus layer, bringing the same transactional protection to consensus mechanisms. By ensuring that validator nodes use post-quantum cryptographic authentication, adversaries cannot forge post-quantum authentication signatures or influence the consensus mechanism. The framework incorporates post-quantum secure multi-party computation (MPC) to preserve the resistance of node selection and block validation against classical and quantum-based cyber attacks.

By fusing classical cryptography robustness with quantum-safe innovations, QuantumShield-BC embodies a transformation in the landscape of blockchain security. The framework combines encryption with lattice-based digital signatures, QKD-secured communication, QRNG-enhanced randomness, and a quantum-resistant consensus protocol to create a next-generation, tamper-proof blockchain ecosystem. With the continued evolution of quantum technology, the fundamental need for a quantum-secured, decentralized system is heightened. In an era where quantum adversaries pose a potential risk, QuantumShield-BC provides the ideal future-proof solution, safeguarding the integrity of blockchain applications across multiple domains.

The workflow diagram of QuantumShield-BC, shown in Fig. 2, illustrates the complete lifecycle of a blockchain transaction secured against quantum threats. It begins with a user-initiated transaction digitally signed using post-quantum cryptography. The transaction is then securely transmitted across blockchain nodes using quantum key distribution (QKD). Validators authenticate the transaction using lattice-based signatures, followed by QRNG-based leader selection to ensure unbiased consensus initiation. The Quantum Byzantine Fault Tolerance (Q-BFT) protocol is executed for multi-party consensus, and upon reaching agreement, the block is finalized and appended to the blockchain. The user receives a confirmation, completing the secure and quantum-resilient transaction flow.

Table 1 presents the key notations used throughout the QuantumShield-BC framework, defining symbols related to transactions, cryptographic operations, consensus mechanisms, quantum processes, and validator interactions in blockchain.

Quantum-secure blockchain layer

The QuantumShield-BC builds a quantum-safe layer on top of the BC, protecting it from quantum adversaries across all three layers (transaction validation, block generation, and ledger) using PQ cryptographic methods. This layer provides the option to replace traditional cryptographic primitives with post-quantum digital signatures and merge quantum-safe hash functions, aided by quantum random number generation (QRNG) to increase entropy in the blockchain. These changes further bolster the blockchain against key stealing, signature forgery, and entropy-based attacks that may become possible with the emergence of quantum CPUs.

Digital signatures are crucial in verifying the authenticity of a transaction and preventing third-party manipulation. Unlike classical cryptographic schemes like RSA or ECDSA, which rely on Shor’s algorithm, QuantumShield-BC adopts a cryptographic stance when it comes to signing and verifying transactions, utilizing PQC algorithms such as CRYSTALS-Dilithium or Falcon post-quantum cryptographic (PQC) technology. The function for transaction verification is defined by

Where (:Vleft(Tright)) is the validity of the transaction, (:{S}_{k}) is the post-quantum digital signature produced with the private key, and (:Hleft(Tright)) is the cryptographic hash of the transaction. The function (:{Verify}_{PQ}) insures that the transaction is signed using a cryptosystem resistant to quantum computations before being included in the blockchain.

The security of the blockchain relies on more secure block generators, which allow data integrity to be secured while still maintaining immutability. QuantumShield-BC: Each block in QuantumShield-BC is tied to the previous one using a quantum-resistant hashing function. The hash of a block can be computed using a post-quantum secure hash function, such as SPHINCS + or Keccak, providing resistance to Grover’s search algorithm. The computation of the block hash is given by

Where (:Hleft({B}_{n}right)) is the hash of the block (:{B}_{n}), (:{B}_{n-1}) is the hash of the previous block, (:{T}_{n}) stands for the transactions that the block contains and (:{S}_{n}) is a digital signature of the block. The function (:{Hash}_{PQ}) secures the hash process against quantum computing attacks.

One of the fundamental weaknesses of classical blockchains is the use of deterministic pseudo-random number generators (DPRNG), which can be vulnerable to entropy prediction attacks. To mitigate this, QuantumShield-BC leverages quantum random number generation (QRNG) to introduce high-entropy randomness in cryptographic operations, such as block generation and nonce generation in smart contracts. We define the quantum entropy function by the following:

Where (:{R}_{Q}) is the quantum entropy, (:QB) is the quantum bits, seqi is the probability for each quantum state. This feature guarantees that roll results are at random, free from the weak state seeds.

QuantumShield-BC also interfaces to a quantum-resistant Merkle tree for secure ledger storage. It is interesting to note that classic Merkle trees are based on hash-based proof of eligibility and could not be trusted alone in the presence of a quantum attack. The approach replaces traditional construction with a post-quantum Merkle tree where each node is signed through a lattice-based DS. The Merkle root calculation is given by

Where (:{M}_{R}) is the post-quantum Merkle root, and (:{L}_{1}parallel:{L}_{2}dots:parallel:{L}_{n}) are the signed transaction leaves. By combining post-quantum signatures at every node layer, the transaction integrity is preserved against quantum adversaries.

QuantumHyperledger/QuantumShield-BC distinguishes itself as a tamper-resistant and robust decentralized ledger via the QRL by combining post-quantum digital signatures, hash hardening algorithms, and QRNG-based entropy. These improvements keep the blockchain operational and resilient to quantum-computing attack vectors as they emerge, meaning that QuantumShield-BC is the future of decentralized, secure applications.

Quantum key distribution (QKD) for secure peer-to-peer communication

QuantumShield-BC enhances blockchain security by utilizing Quantum Key Distribution (QKD) for secure peer-to-peer communication, thereby protecting the cryptographic keys exchanged between blockchain nodes against quantum attacks. Figure 3 illustrates that classic key-exchange mechanisms in cryptography, such as RSA and Diffie-Hellman, lack security against Shor’s algorithm in traditional blockchain networks. QKD, on the other hand, can provide the generation and secure transmission of cryptographic keys based on quantum states, for which eavesdropping and key compromise are not feasible.

Protected by the no-cloning theorem and superposition in quantum mechanics, 7 QKD allows for an intercept-resilient exchange of cryptographic keys. QuantumShield-BC utilizes the BB84 protocol to exchange a key between the sender and receiver blockchain nodes via quantum state-encoded, polarized photons. The key exchange can then be mathematically described.

Where (:K) denotes the obtained secret key, (:{Q}_{S}) is the quantum state transmitted by the sender node, and (:{Q}_{R}) is the quantum state received by the recipient node. If the eavesdropper attempts to tap the quantum channel, the organization of the quantum state collapses, informing the communicating parties.

After the Quantum Key is exchanged successfully, it is applied to build a safe symmetric encryption channel between blockchain nodes. By encrypting, the transmitted blockchain data is kept private and secure. The encryption with the key generated by the QKD is defined as.

Where (:C) is the encrypted message, (:{E}_{K}left(Mright)) is encryption with the secret key (:K), and (oplus)it is the XOR operation. The recipient decrypts the message with

Here (:{D}_{K}left(Cright)) is the cryptographic decryption operation. Since the encryption key is securely exchanged by using the QKD, the communication is secure against quantum decoherence attacks.

QuantumShield-BC also included post-quantum cryptographic algorithms to supplement QKD in addition to secure key exchange. QKD provides the guarantee of key confidentiality, and post-quantum key encapsulation mechanisms (KEM), such as Kyber and FrodoKEM, are applied to achieve hybrid security for blockchain data exchange. The hybrid encryption, combining QKD and lattice-based encryption, aims to protect against vulnerabilities in one security layer by ensuring the other remains secure. Denote the hybrid key agreement function by

where (:{K}_{H}) is the hybrid secret key for secure communication, (:{K}_{QKD}) is the secret key generated from qa quantum source, and cap K sub cap P cap Q cap C is the key from a post-quantumkey encapsulation mechanism.

QKD-authentication based mechanisms also add a layer of security to blockchain communications. Validator nodes in the blockchain network are authenticated by quantum-secure key exchange method and can defend against Sybil and identity cues attacks. A key QKD-authenticated identity hash is generated in each validator node, as follows:

Where (:{H}_{V}) is the identity of the authenticated validator, (:{ID}_{V}) is the unique identifier for the node, and (:K) is the QKD-derived key. This allows consensus and block validation only by nodes that are quantum-authenticated.

By using QKD for secure key exchange, QuantumShield-BC Se mitigates the risks associated with classical key exchange protocols and adds layer of post-quantum encryption. QKD is integrated with hybrid encryption schemes and QKD-authenticated node validation to secure the blockchain against classical and quantum attack fronts. With this, QuantumShield-BC establishes a channel for communication that will remain for the decentralized networks of the blockchain’s future.

Practical deployment considerations

Theoretically unbreakable, Quantum Key Distribution (QKD) provides secure key exchange; however, practical implementations raise several issues. The significant challenges include the high hardware costs of quantum photon sources, detectors, and synchronization systems, as well as channel loss over long distances, particularly when the channel is a fiber-optic or free-space link. In addition, the scalability of QKD is limited for blockchain networks because of the requirement of individual quantum channels among the nodes. QuantumShield-BC addresses these concerns, supporting a modular integration that allows hybrid PQC-KEM mechanisms to supplement QKD in situations where its deployment is not feasible. Future improvements will investigate satellite-based QKD or trusted node relays to eliminate losses caused by distance and increase the practical applicability of the system.

Quantum-secure consensus mechanism

Introducing a quantum-secure consensus, QuantumShield-BC enhances the security of the blockchain by utilizing post-quantum cryptographic algorithms with Byzantine Fault Tolerance (BFT), as illustrated in Fig. 4. Classic consensus schemes, such as PoW and PoS, are based on cryptographic algorithms that are susceptible to quantum attacks (e.g., Shor’s algorithm, which can crack RSA and ECC). It is ensured that the proposed Q-BFT-based protocol is secure for block validation and transaction verification even in the quantum environment.

In QuantumShield-BC, each validator node is required to verify transactions with a post-quantum cryptographic signature before contributing to the consensus. The authentication is formed using lattice-based digital signatures, so malicious parties cannot forge the validator credentials. The function is the validator authentication function assigned by where quale lector.

where (:{V}_{node}) denotes the validator at the position 1the validator’s authenticating status at the position, (:{S}_{v}) is the post-quantum digital signature produced by the validator at the 11 st position, and cap H of cap B is the cryptographic hashrecord of the candidate block. This prevents the Byzantine Army from joining the consensus by only accepting quantum-resistant signatures to verify a block.

This consensus decision function collects multiple signatures of validator nodes, and the block is appended to the blockchain only if a large enough set of quantum-authenticated validators accept it. This is mathematically modeled as:

Where (:{C}_{V}) is the consensus declared voting result, (:{T}_{i}) is any individual transaction of a block, and (:{P}_{i}) is the post-quantum public key of the validator (::i). QiatumShield-BC can defend against attacks such as quantum Sybil attacks and signature forging by implementing this quantum-secure aggregation process.

QuantumShield-BC uses quantum-resistant threshold cryptography to guarantee that block finalization is not possible unless a sufficiently large number of validators participate. The block confirmation horizon can be derived as follows:

Where (:{Q}_{C}) is a quantum consensus threshold, (:{V}_{{node}_{i}}) is the verification status of single validator nodes, and (:tau:) is a minimum threshold required for consensus. This maintains decentralization in the blockchain and thwart quantum bloc adversaries attempts to effect block finalization.

Leader election in consensus protocols is generally susceptible to predictability attacks. QuantumShield-BC addresses this challenge by using QRNG for unbiased leader election. The leader selection function that uses QRNGs has the form of

Where (:L) is the leader node, (:{R}_{Q}) is the quantum-generated random number, and nn denotes the total number of the validators that participate in the procedure. Thanks to the use of QRNG, QuantumShield-BC makes sure leader election mysterious and non-manipulatable.

In QuantumShield-BC (QSB)-QRNGs are not augmentations of conventional PRNGs(2), but separated quantum entropy sources based on physical behavior of quantum systems. QRNGs, however, take their source of randomness from fundamentally unpredictable quantum processes (such as photon phase noise, radioactive decay, or vacuum fluctuations), in contrast to PRNGs, which rely on deterministic algorithms and seed value(s). Such sources are physically uncloneable and therefore they cannot be mimicked so that they not only quantum mechanically sounds more secure than classical random numbers, but they are not just probabilistically secure (cloning the classical data is a typical classical attack), but they are also physically verifiable. To avoid being attacked by entropy predictability, QuantumShield-BC employs QRNG generated values for leader selection, nonce generation and consensus randomness. Randomness is fed through quantum-proof extractors (such as Trevisan’s extractor) for entropy extraction and uniformity, making the output cryptographically usable (see²⁰ for specifics on the entropy extraction process).

For additional security, the architecture includes a hybrid consensus validation scheme with the quantum multiparty computation (QMPC). This way, several validators can cooperate in validating transactions and without revealing too much about the sensitive cryptographical information. The centralized verification process over multi-party consensus is defined as

.

Where (:{M}_{C}) is the consensus verification output, (:{S}_{i}) is the post-quantum digital signature of the validator (:i), and (:Hleft({T}_{i}right)) is the CM-Hash of the transaction (:{T}_{i}). QuantumShield-BC achieves privacy preserving and quantum-safe consensus validation by using QMPC.

By combining QRPoA with PQC-threshold signature, QRNG leader selection, and QMPC consensus validation, QuantumShield-BC is secure against classical and quantum adversarial attacks. This method allows decentralized blockchain systems to achieve the tamper-proof and security in the quantum scale era because of large-scale quantum computer, and it makes QuantumShield-BC as a future next-generation blockchain consensus framework.

Implementation of quantumshield-BC prototype

The development of the quantumshield-bc prototype takes place in several stages to enable a step-by-step integration of quantum-safe blockchain components. In addition to a post-quantum cryptography (PQC), the OmegaLedger prototype includes quantum key distribution (QKD), quantum-secure consensus algorithms, and quantum random number generation (QRNG) as solutions to boost blockchain immunity against quantum attacks. At each stage, critical security concerns, that is transaction verification, block creation, consensus assurance, and secure p2p communication, are addressed. The main development steps of the prototype are described below.

The first phase of development focuses on incorporating post-quantum digital signatures to transition from classical signatures, RSA and ECC, to post-quantum. QuantumShield-BC uses lattice-based cryptographic methods CRYSTALS-Dilithium and Falcon by signing transactions, ensuring secure transactions. Where the transaction validation function is the formulation of:

Where (:Vleft(Tright)) is the transaction validity, (:{S}_{k}) is the post-quantum digital signature of the sender of the transaction and (:Hleft(Tright)) is the cryptographic hash of the transaction. This prevents non quantum-resistant signatures from being added to the blockchain.

In the second stage, the communication between nodes are being insured using QKD, where nodes use QKD to share an encrypting/decrypting key for the block chain communication. This also closes weaknesses in traditional key exchange schemes like Diffie-Hellman and RSA. The pairwise key agreement between nodes is specified as:

Where (:K) is the parties’ secret key, (::{Q}_{S}) is the quantum state sent by the sender, (:{Q}_{R}) and is the received quantum state of the receiver. If the key is intercepted by an enemy, he will change the quantum state; therefore, key compromise will be noticed immediately.

To derive tamper-proof block generation, QuantumShield-BC employs quantum-resistant hashing for connecting the blocks together within the blockchain. The block hash calculation uses SPHINCS + or Keccak, which are resistant to Grover algorithm attacks. The hash function used to create a block is defined as:

Where (:Hleft({B}_{n}right)) is a hash to the newly created block (:{B}_{n}), (:{B}_{n-1}) to the previous block, (:{T}_{n}) to the transactions in the block; and (:{S}_{n}) is the post-quantum block signature. This ensures that the data cannot be changed and that it will be resistant to quantum attacks.

The upcoming developments will be directed towards the implementation of Quantum Byzantine Fault Tolerance (Q-BFT), a post-quantum consensus protocol that supersedes old-fashioned PoS and PoW mechanisms. It was also observed that validator nodes prove their identity with quantum-secure signatures before joining the consensus. The function for the validator authentication is defined as

Where (:{V}_{node}) denotes validator certification, (:{S}_{v}) is the post-quantum digital signature of the validator, and (:Hleft(Bright)) is the cryptographic hash of the block proposal. Only verified QSC validators are allowed to participate in the consensus.

To achieve the fair leadership selection in consensus, the Quantum Random Number Generation (QRNG) is implemented in order to remove the bias and predictability during the leader selection. We model the leader election as

Where (:L) is the leader, (:{R}_{Q}) is the random number generated by quantum, and (:n) is the number of available validators. QuantumShield-BC relies on QRNG to achieve fair and tamper-free leader election free from pseudo randomness source such as pseudo-random number generator and pseudo-random counterparts.

The last stage comprises the installation of QuantumShield-BC prototype on a testbed for testing its security and performance as well as its defence to quantum attacks. The security of transaction verification, consensus and block generation is proven with quantum attack simulation on quantum computing simulator (i.e., IBM Qiskit or Google Cirq). The integrity of the global blockchain is decided by the multi-party consensus verification function, which is denoted as:

Where (:{M}_{C}) is the consensus validation status, (:{S}_{i}) is the digital signature of validator post-quantum (:i), and (:Hleft({T}_{i}right)) is the hash cryptographic value of transaction (:{T}_{i}). This multi-party validation prevent any but quantum-secure transactions from entering the blockchain.

Incorporating PQ digital signatures, PKI free QKD, quantum-secure hashing, and QRNG-based consensus, the QuantumShield-BC prototype provides an ultra-resilient and temper-proof blockchain platform. By the systematic evolution and incorporation of quantum-safe technology into a blockchain, so that the blockchain is operational, scalable and robust against newly emerging quantum scientific threats, a future user facing quantum-safe blockchain 2.0 can be achieved.

Proposed algorithms

This section presents the core algorithms underpinning the QuantumShield-BC framework. Each algorithm addresses a specific component of the system, including transaction authentication, secure key exchange, quantum-safe consensus, and randomness generation. Together, these algorithms ensure end-to-end quantum resilience, enabling secure, scalable, and tamper-proof blockchain operations in the presence of emerging quantum computational threats.

Algorithm 1 secures blockchain transactions using post-quantum digital signatures. It begins by hashing the transaction data and generating a signature with a private key using a post-quantum algorithm. The signature is then attached to the transaction and verified using the corresponding public key. This ensures that the transaction is authentic, tamper-proof, and resistant to quantum-based attacks.

Algorithm 2 enables secure key exchange between blockchain nodes using quantum key distribution. The sender transmits quantum states, which the receiver measures using random bases. Through classical communication, both parties compare bases and retain matching bits to form a raw key. After error correction and privacy amplification, a final secure key is established, ensuring tamper-proof communication against quantum adversaries.

Algorithm 3 generates a quantum-resistant hash for a blockchain block using post-quantum cryptographic functions. It concatenates the current block data with the previous block’s hash to form the input. A secure hash function, such as SPHINCS + or Keccak, is then applied to produce a tamper-proof hash. This ensures the integrity and immutability of the blockchain ledger.

Algorithm 4 performs transaction validation using post-quantum cryptographic techniques. It extracts the transaction and its digital signature, computes the hash of the transaction, and verifies the signature using the sender’s public key. If the verification is successful, the transaction is accepted; otherwise, it is rejected. This process ensures that only authentic and quantum-secure transactions enter the blockchain.

Algorithm 5 generates quantum-secure random numbers using a quantum random number generator (QRNG). It begins by producing a sequence of quantum bits, which are measured to obtain raw entropy. A randomness extraction function is then applied to refine the output. The resulting value provides true, unpredictable randomness used for nonce generation, leader selection, and other critical blockchain processes.

Algorithm 6 selects a consensus leader using quantum-generated randomness. A random number is generated via a quantum random number generator (QRNG) and mapped to a validator index by taking the modulus with the total number of validators. If the selected validator is active, it is assigned as the leader. This approach ensures fair, unpredictable, and tamper-proof leader selection.

Algorithm 7 establishes consensus using the Quantum Byzantine Fault Tolerance (Q-BFT) mechanism. Each validator verifies transactions using post-quantum signatures and broadcasts its result. The system aggregates validator votes and compares them against a predefined threshold. If the number of valid votes meets or exceeds this threshold, consensus is achieved and the block is approved; otherwise, consensus fails and is retried.

Algorithm 8 performs post-quantum multi-party consensus verification among validators. Each validator independently verifies transaction signatures using post-quantum cryptography. The results are securely shared and aggregated using quantum-secure multi-party computation. If all verifications are successful, consensus is confirmed. Otherwise, the transaction is rejected. This ensures tamper-resistant validation across distributed nodes in a quantum-secure blockchain environment.

Algorithm 9 finalizes and appends a validated block to the blockchain. It first checks whether consensus has been achieved. If valid, the block data is hashed using a post-quantum secure hash function and linked to the previous block. The finalized block is then added to the blockchain and broadcast to the network, ensuring integrity, immutability, and resistance to quantum-based tampering.

Algorithm 10 secures validator communication using quantum-aware techniques. It begins by establishing a key via quantum key distribution, followed by validator authentication using post-quantum signatures. All messages are encrypted using the QKD-derived key. Replay and Sybil attacks are mitigated through QRNG-generated nonces and identity checks. The system ensures quantum-resilient, authenticated, and tamper-proof communication across blockchain nodes.

Performance evaluation metrics

Performance Evaluation The performance of QuantumShield-BC is tested through a number of essential performance criteria to measure its security, efficiency, and scalability against quantum threats. The assessment considers transaction validation latency, consensus throughput, cryptographic entropy, and benchmark quantum resistance. These benchmarks guarantee QuantumShield-BC maintains high speed operation and uses post-quantum cryptographic (PQC) primitives, QKD, Quantum Byzantine Fault Tolerance (Q-BFT), and QRNG.

One of the primary performance metrics is the transaction validation time, which measures the time to validate a transaction using post-quantum digital signatures as opposed to the case of standard signatures. The validation time ({T}_{v}) of a transaction can be defined as

Where (:{T}_{Sign}) is the time to compute a post-quantum signature, and (:{T}_{Verify}) is the time to verify the signature based on the underlying post-quantum cryptographic (PQC) scheme. Since lattice-based signatures (e.g., CRYSTALS-Dilithium, Falcon) increase the computational overhead as compared to ECC, we strive to choose PQC schemes with the least latency, to achieve the most efficient QuantumShield-BC.

Another essential metric to consider is consensus throughput, the number of transactions that can be handled per second and that are secure against quantum adversaries. The performance (throughput) of the Q-BFT consensus mechanism can be defined as

Where (:{T}_{Q-BFT}) is the number of transactions (transactions per second), (:{N}_{T}) is the number of transactions validated (:,:cap:T:sub:cap:C:is:the:total:running:time:for:forming:a)decision. Utilizing Quantum-Secure Multi-Party Computation (QMPC), the consensus mechanism ensures secure transaction validation, whilst minimizing the computational overhead caused by post-quantum cryptographic primitives.

QuantumShield-BC, in selecting specific PQC algorithms, makes a balance between computational efficiency and post-quantum security guarantees. We considered both CRYSTALS-Dilithium and Falcon schemes as digital signatures, both of which are NIST post-quantum cryptography standardization finalists. CRYSTALS-Dilithium provides excellent security guarantees and high confidence in being resilient against lattice-based attacks; however, Falcon supports very small signatures with much faster verification speeds, making it more advantageous for high-throughput blockchain environments. We used Falcon for consensus authentication in our prototype, due to its fast signature verification time (1.5 ms per signature), and we opted for Dilithium for transaction signing, where the signature size constraint is less critical. The combination of the two reduces both speed and storage overhead used by the two to perform blockchain operations. We found that total conversion to Dilithium increases validation time by 18%, but this also improves resistance to some attacks based on side-channels¹⁷. These design choices exemplify how modular PQC algorithm customization can align security-performance trade-offs for real systems.

An entropy assessment of QRNG-based blockchain functions is conducted to evaluate the quality of randomness applied to leader selection, nonce generation, and cryptographic key generation tasks. The Shannon entropy formula determines the quantum entropy value, cap R sub cap Qalue, (:{R}_{Q}), is determined by the Shannon entropy formula:

Where (:QB) is the bit pattern ggenerated from the quantum, and p sub i is the probability distribution of the uantum state. Higher entropy values imply better randomness, increased security for cryptographic keys, and greater unpredictability in blockchain operations.

Equation (23) computes the Shannon entropy value derived from quantum bitstreams generated by a QRNG device. Here, the entropy H(Q)=(:-sum:_{i}{p}_{i}{log}_{2}:{p}_{i}) ​ quantifies the uncertainty of measured quantum states. Unlike classical bitstreams, the probabilities (:{p}_{i})​ are obtained from quantum state measurement results, ensuring they reflect hardware-derived unpredictability rather than algorithmic randomness.

In order to measure the quantum resistance of blockchain transactions, we analyze security by running simulations using Shor’s Algorithm to compare the resistance of classical versus post-quantum cryptography. The time complexity for solving the cryptographic key with Shor’s algorithm can be expressed as: $ where ta is the time to guess a while Shor’s key is around Inf:.

Where (:N:indicates:the:length:of) the cryptographic key in bits, since RSA/ECC keys will be broken in polynomial time by Shor’s algorithm, QuantumShield-BC is based on post-quantum cryptographic primitives like Kyber, FrodoKEM, and SPHINCS + that are secure against quantum decryption.

Another relevant measure is the network overhead due to QKD-based encryption. However, QKD’s secure key distribution may lead to extra bandwidth consumption, where cap O sub cap Q is the overhead factor.

Where (:{B}_{Q}) denotes the bandwidth cconsumption of QKD-based encryption, a nd (:{B}_{C}) denotes classical encryption. QuantumShield-BC is lightweight, and the overall communication efficiency is not degraded as QKD key exchange rates are improved and unnecessary quantum-state transmissions are suppressed.

The last evaluation measure is the CTT: the time it takes the network to agree upon a new block and place it on the blockchain. This is given by

Where (:{T}_{B}) is the block confirmation time, (:{T}_{Comm}) denotes the time for communication among validators, (:{T}_{Q-Rand}) is the time for quantum-safe random value generation for leader selection and (:{V}_{C}) is the number of the validators involved. The efficient block generation is one of the most essential requirements of the blockchain with a shorter block confirmation time and quantum resistance.

This allows QuantumShield-BC to be tested against the following performance measures, namely, transaction validation latency, consensus throughput, entropy test, quantum safety test, QKD-induced network overhead, and block confirmation time, to strike a tradeoff among security, efficiency, and scalability. These results support that the insertion of quantum-safe cryptographic features improves the resilience of blockchain-based networks against quantum threats with negligible performance degradation.

Key novelties of QuantumShield-BC

QuantumShield-BC provides a unique and functionally integrated quantum-secure blockchain structure which incorporates post-quantum digital signatures, secure communication through QKD, leader election based on QRNG, and a new Q-BFT consensus protocol in a single framework. In contrast to earlier efforts to improve the security of respective quantum individual layer (PQCs only/QKDs only) QuantumShield-BC is a an integrated layered solution with protocol-level modularity, consolidated quantum cryptographic implementations on each layer (transaction, network and consensus layer, respectively) with an extensive use of quantum secure systems inherent across the multiple layers of the infrastructure. By validation, the prototype embodies a tangible performance benefit over 7000 TPS at 100 validators, and full quantum resistance to Sybil, replay, and MITM attacks, verified through detailed ablation studies quantifying the contribution of each quantum component.

The main novelty of QuantumShield-BC is the use of post-quantum cryptographic (PQC) signatures instead of classical digital signatures, which helps secure transactions against quantum adversaries. Most existing blockchain systems rely on the ECDSA, a cryptographic algorithm whose security can be effectively compromised by applying Shor’s algorithm. Including lattice-based signature schemes, CRYSTALS-Dilithium and Falcon, makes the framework resistant to compromise through quantum-enabled keys. These post-quantum signatures exhibit computational infeasibility for signature forgery but enable efficient transaction validation, thereby preserving blockchain security against the post-quantum threat.

It also features the first-time integration of quantum key distribution (QKD) to achieve safe transport over single-mode fiber-based node-to-node communication by preventing eavesdropping or interception of encryption keys. Quantum computers decrypt public-private key cryptography used in traditional blockchains. Based on quantum mechanics, QKD guarantees that eavesdropping on cryptographic keys disturbs their quantum state, making such efforts detectable. This innovation allows blockchain nodes to securely send encryption keys to each other, creating a quantum-resistant peer-to-peer communication mechanism that cannot be attacked by a man-in-the-middle (MITM).

The second main element of innovation of QuantumShield-BC is the Quantum Byzantine Fault Tolerance (Q-BFT) consensus mechanism that strengthens the fault tolerance of blockchain validators. Sybil Attack Resistant — Classic consensus protocols like PoW and PoS are sybil attack resistant (if an attacker has the majority of computing power or stake, they can process any valid transaction). Using post-quantum digital signatures and multi-party secure computation, Q-BFT guarantees that only quantum-authenticated validators can form consensus. This ensures that adversaries with quantum capabilities cannot control the network and that trust remains decentralized.

An even more fundamental feature of QuantumShield-BC is the application of quantum random number generation (QRNG), which helps with the significant level of unpredictability needed in key cryptographic processes; not just that block generation, nonce selection, and brilliant contract execution are entirely random (all of which can be compromised by classical deterministic PRNGs). Blockchain systems are susceptible to replay attacks and nonce manipulations because classical pseudo-random number generators (PRNGs) allow for an entropy prediction attack¹⁹. QRNG is based on the quantum mechanical principles of superposition and randomness extraction, offering a genuinely unpredictable entropy source: this guarantees that cryptographic randomness is tamper-evident and immune to deterministic weaknesses intrinsic to all classical PRNGs.

In addition to regular blockchain storage, QuantumShield-BC ensures the security of blockchain storage with quantum-resistant hashing techniques, maintaining the characteristics of immutability in the face of quantum attacks. It also means that traditional hashes, like SHA-256, are vulnerable to Grover’s algorithm, and using it on hashes doubles the effectiveness of brute-force attacks against traditional cryptographic hashes. To counter this, the framework uses hash-based digital signatures such as SPHINCS + and quantum-resistant hashing algorithms such as Keccak, which are believed to have a high degree of resistance against potential quantum computational speed-ups. This ensures that blockchain ledger data is secure and unalterable by any quantum computer that can currently break conventional hashing functions.

The leader selection mechanism of a consensus mechanism is generally vulnerable to predictability attacks, because attackers can try to control the election result by using the deterministic randomness source in the leader election process on the blockchain. QuantumShield-BC addresses this issue by utilizing QRNG for leader selection, resulting in an entirely random and immutable selection of validators. While traditional leader election mechanisms are based on deterministic algorithms, the use of quantum-generated randomness prevents the adversarial influence of private information, ensuring safety and transparency in blockchain governance.

In addition, the framework also provides a hybrid cryptographic scheme that merges QKD and post-quantum key encapsulation mechanisms (PQC-KEM), including Kyber and FrodoKEM^17,51. Our hybrid encryption scheme preserves the security of the secondary post-quantum encryption layer even under a compromise of QKD due to implementation-layer issues. Through dual-layer encryption, QuantumShield-BC is more resistant than previous solutions against classical and quantum cyber threats, offering strong security assurances for blockchain transactions and innovative contract executions.

One of the additional characteristics of QuantumShield-BC is that it is resilient to quantum-enhanced replay attacks. For instance, classical blockchains use nonce verification to ensure no transaction occurs twice (essentially timestamp-based checks for duplicates), but using the quantum computer to essentially time travel and trigger a validation bypass by the device’s incorrect timestamps. By integrating QRNG, it is guaranteed that a truly quantum-generated atom is used to generate the next transaction nonce, making any potential replay of an old transaction impossible. These security measures make blockchain transactions highly secure and enable strong protection against double-spending and duplication attacks, which cannot even be carried forward in a quantum computing environment.

QuantumShield-BC is a new kind of quantum-secure blockchain architecture that synergistically integrates these innovations to help make decentralized systems quantum-resistant for years to come. This means that integrating post-quantum cryptography, quantum key distribution, QRNG, and Q-BFT consensus helps to protect against quantum attacks on each part of the blockchain. QuantumShield-BC not only defines a benchmark for secure, decentralized, and tamper-proof blockchain ecosystems but also runs on an out-of-the-box quantum-resilience framework, as opposed to the traditional blockchain systems that will need first-order cryptographic upgrades to maintain their post-quantum securability.

To summarize, the key innovation of QuantumShield-BC include integration in single protocol level of post-quantum digital signature, quantum-key-distribution and quantum-random-number generator coupled with a new Quantum Byzantine Fault Tolerance (Q-BFT) consensus algorithm. Although prior work tends to analyse such technologies in a loose setting or a restricted manner together, QuantumShield-BC enables a complete modular and end-to-end architecture with scalability and quantum resistance empirical performance validation. The unification of cryptographic, communication and consensus resilience into a single deployable blockchain framework is the central contribution of our work.