Architectural placement of post-quantum digital signatures ML-DSA and SLH-DSA in blockchain systems

The migration of distributed ledgers to post-quantum digital signatures is commonly reduced to replacing the signature algorithm. In a blockchain system, however, the signature governs not only cryptographic authentication but also the transaction size, block density, chain growth rate, throughput and block verification time. This study experimentally assesses the architectural consequences of placing the post-quantum signatures ML-DSA and SLH-DSA at four levels, namely per-transaction signing, hybrid per-transaction signing, signing of the block header by a validator node, and signing of a checkpoint. Twenty-three schemes were examined, including two classical schemes, three ML-DSA variants, twelve SLH-DSA variants and six hybrid schemes; six thousand nine hundred measurements of key generation, signing and verification were performed and complemented by a simulation of block density and verification time. It is shown that even the most compact post-quantum scheme, when the signature is placed in every transaction, reduces block density and throughput almost fifteenfold, while for the full family of hash-based schemes the density drop reaches thirty to one hundred ninety-three times, whereas signing the block header or a checkpoint increases chain growth by no more than one and a half percent. The principal result is that the architectural level of signature placement is an independent factor of the suitability of a post-quantum scheme, since the same scheme may be unacceptable at the transaction level yet practically applicable at the block or checkpoint level.

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