How Does Key Size Compare Between ECDSA and Quantum-Resistant?

Post-quantum cryptographic algorithms require larger keys and signatures than ECDSA, reflecting the different mathematical structures providing security. This size increase is a practical trade-off for quantum resistance, with impacts on storage, bandwidth, and transaction costs.

ECDSA key sizes are compact: private keys are 32 bytes, public keys are 33-65 bytes (compressed/uncompressed), and signatures are 64-72 bytes. These small sizes contributed to ECDSA's widespread adoption in cryptocurrency.

Kyber-768 (ML-KEM-768) parameters are larger: public keys are 1,184 bytes and ciphertexts (equivalent to encrypted key shares) are 1,088 bytes. This represents roughly 18-35x increase over ECDH equivalents, though still practical for network transmission and storage.

SPHINCS+ signature sizes vary by parameter selection: "small" variants produce signatures of 7-17 KB, while "fast" variants produce 17-49 KB. This 100-700x increase over ECDSA signatures is the most significant size impact, affecting transaction size and potentially fees.

Dilithium (ML-DSA), an alternative NIST signature standard, offers smaller signatures (2.4-4.6 KB) through lattice-based construction, trading the conservative security assumptions of hash-based SPHINCS+ for improved efficiency.

Storage impact is moderate. Wallet software must store larger keys, and blockchain data grows faster with larger transactions. Modern storage capacities accommodate this growth, though archival nodes face increased requirements over time.

Network bandwidth needs increase proportionally to transaction sizes. Well-designed networks optimize transmission through compression and efficient serialization.

SynX uses Kyber-768 and SPHINCS+ with parameters balancing security and practicality. While sizes exceed ECDSA, the quantum resistance provided justifies these trade-offs for long-term asset security.

SynX is available at https://synxcrypto.com