1. Understanding the technology
What is post-quantum cryptography?
Post-quantum cryptography, or PQC, uses mathematical algorithms designed to resist attacks from both conventional and quantum computers. It includes digital signatures and mechanisms for establishing shared secrets. These algorithms run on conventional computers; quantum hardware is not required to use them.
How is post-quantum cryptography different from quantum cryptography?
Post-quantum cryptography uses mathematical algorithms on conventional hardware. Quantum cryptography uses properties of quantum physics directly, often with specialised equipment. Quantum key distribution is one example. The two approaches address security through different mechanisms.
Are post-quantum signatures the same as post-quantum encryption?
No. Digital signatures verify authorization and help detect changes to a message. Encryption protects confidentiality. For example, ML-DSA and SLH-DSA are signature algorithms, while ML-KEM establishes shared secrets that can support encrypted communication.
Does “quantum-resistant” mean an algorithm can never be broken?
No. It means the algorithm is designed to withstand known quantum attacks under its security assumptions. Security also depends on implementation, parameters, and key management. Continuing research and the ability to replace algorithms remain important parts of long-term protection against quantum attacks.
2. Understanding the quantum threat
Why could quantum computers threaten blockchain security?
Many blockchains use elliptic-curve digital signatures to authorize transactions. A sufficiently powerful quantum computer running Shor’s algorithm could derive a private key from its public key, potentially allowing an attacker to forge signatures. The risk depends on the cryptography and design of each blockchain.
Can quantum computers break cryptocurrency security today?
No quantum computer capable of threatening the elliptic-curve signatures used by major blockchains is known to exist today. However, preparing for that possibility requires changes across protocols, wallets, applications, and infrastructure, which take time to coordinate.
When could quantum computers become a practical threat?
There is no confirmed date. Practical attacks depend on advances in hardware, error correction, and algorithms. Research estimates the resources attacks might require, but those estimates do not establish when a capable machine will exist. Predictions of a specific “Q-Day” have been estimated to arrive as early as 2029.
Is “harvest now, decrypt later” the main quantum risk for blockchains?
It is a risk for encrypted information that needs to remain confidential over time. Public blockchain transactions are generally visible already, so their central quantum concern is often signature forgery rather than decryption. Organizations using blockchains should assess both transaction integrity and the confidentiality of connected systems.
3. Understanding blockchain protection
Which parts of a blockchain need post-quantum protection?
Relevant components can include account signatures, consensus messages, participant selection, and proofs used by external systems. Wallets, custody systems, and application permissions also need assessment. Each component has its own cryptographic dependencies, so protection should be evaluated layer by layer.
Does a post-quantum wallet protect the entire blockchain?
No. Post-quantum signing can strengthen transaction authorisation for an account. It does not automatically replace the cryptography used by consensus, other accounts, or connected applications. Wallet capabilities and network-wide protection should be described separately.
Are blockchain hash functions vulnerable in the same way as digital signatures?
No. Shor’s algorithm threatens certain public-key systems, including elliptic-curve signatures. Grover’s algorithm affects search-based attacks on hashes and symmetric cryptography differently. The appropriate response depends on the algorithm, its parameters, and how it is used.
Does using multiple signing keys automatically provide quantum resistance?
No. Requiring several signatures does not remove a vulnerability shared by every signing algorithm. A post-quantum or hybrid multisignature arrangement must use suitable algorithms and an approval policy that preserves the intended protection. The choice between requiring both signature types and accepting either matters.
4. Preparing for migration
Why prepare before a powerful quantum computer exists?
Migration involves identifying cryptographic dependencies, choosing replacements, updating systems, and testing compatibility. Starting early gives organizations time to resolve these dependencies and coordinate with suppliers. The National Institute of Standards and Technology (NIST) encourages organizations to begin preparing for migration to post-quantum cryptography.
What is cryptographic agility, and why does it matter?
Cryptographic agility is the ability to adopt new algorithms and retire vulnerable ones with limited disruption. It helps organizations respond to new research, changing standards, or implementation weaknesses without redesigning their entire system each time.
Does rotating private keys remove quantum vulnerability?
Not necessarily. Replacing a key while retaining the same quantum-vulnerable algorithm leaves that underlying vulnerability in place. Migration may require changing the signature scheme or authorization arrangement, alongside checking that wallets, applications, and infrastructure support the change.
5. Understanding Algorand's approach
Which post-quantum capabilities has Algorand deployed?
Algorand uses Falcon signatures in State Proofs and supports native Falcon-1024 account signatures. We also launched native post-quantum Falcon-1024 accounts on Mainnet in August 2026 through the v5.0.0 upgrade. These capabilities protect transaction history and accounts, respectively, rather than establishing protection across every protocol component.
What is the difference between State Proofs and post-quantum accounts?
State Proofs let external systems verify information about Algorand’s blockchain history using cryptographic attestations. Post-quantum accounts use Falcon-1024 signatures to authorize transactions. They address different needs: verifying blockchain history and controlling account spending.
Are existing Algorand accounts automatically migrated?
No. Existing Ed25519 accounts continue to operate alongside post-quantum accounts. Rekeying from an Edwards account to a Falcon account provides a migration path that can preserve an account’s original public address while changing its spending authority. Compatibility varies across wallets and applications, so users should consult their wallet provider before making changes.
What remains on Algorand’s post-quantum roadmap?
The published roadmap includes further account capabilities and research into consensus signatures and the Verifiable Random Function (VRF) used for committee selection. These areas are separate from deployed account signatures and State Proofs. Planned milestones remain subject to development, research, and evolving standards.
For current implementation details, visit the post-quantum accounts documentation. For planned developments and research, explore the Algorand post-quantum cryptography roadmap.
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