bitcoin-dev

Lamport scheme (not signature) to economize on L1

Lamport scheme (not signature) to economize on L1

Original Postby yurisvb at pm.me

Posted on: December 31, 2023 17:42 UTC

A recent update on a proposed protocol has been shared, detailing significant changes to its key derivation mechanism.

The protocol no longer incorporates the FFM cryptosystem, opting instead for a series of one-way function derivations depicted in a diagram available on GitHub. This structure ensures that the address prior to the current one, denoted as ADDR_(i-1), can be retrieved following the transaction's confirmation a few blocks into the blockchain. This update eliminates concerns about an honest participant losing internet access and facing penalties due to unfulfilled commitments.

The protocol's transaction process is outlined as follows: initially, the sender broadcasts a transaction signed using the Lamport scheme, which alone cannot be verified. Accompanying this is a conventionally signed commitment ensuring the broadcast of the corresponding Lamport pre-image before a set deadline (T2). This commitment temporarily locks the unspent transaction output (UTXO) until the promise is fulfilled, the deadline passes, or a double-spending attempt is detected, at which point fines are imposed to protect the involved miners.

Additionally, the sender broadcasts the Lamport pre-image, encrypted with a symmetric key derived from a lengthy hash connected to a seed included in the bundle. This allows miners to securely access ADDR_(i-1) after the transaction is adequately buried within the blockchain but before the deadline T2, addressing potential issues of the sender being disconnected from the internet.

Once ADDR_(i-1) is decrypted by the miners or broadcast by the sender, the transaction having been integrated into the blockchain, ADDR_(i-1) will be mined, validating the transaction and releasing fees to the miners. At this juncture, the previous private and public keys (PRI_i, PUB_i) are discarded, and ADDR_i takes over from ADDR_(i-1) as the operative address, with ADDR_(i-2) serving as its Lamport pre-image. Should it be the first iteration (i=1), the Lamport chain concludes. With the implementation of 16-byte long addresses and signatures, the on-chain footprint is consolidated to the targeted 32 bytes.

The communication ends with season's greetings, reflecting the informal tone often found in correspondence among colleagues, despite the complex technical content.