BIP-119.2: Extensions for Lightning Symmetry

BIP-119.2: Extensions for Lightning Symmetry

Original Postby jeremy

Posted on: May 6, 2024 18:44 UTC

The recent proposal introduces three new modes to address specific needs in Lightning Symmetry applications, enhancing their functionality and efficiency.

These modes include a 20 Byte Hash160 CTV, along with 21 and 33 Byte CTV options. The latter two variations are designed with an additional byte to indicate the second-to-top stack element that should be included in the hash. This feature is particularly vital for Lightning Symmetry applications, as it allows for the inscription of essential data within a block. Consequently, this enables clients to efficiently delete old channel states, maintaining the system's integrity and performance.

A significant point of discussion revolves around the security implications of using a 20 Byte Hash160. Specifically, there is concern regarding its preimage and collision resistance capabilities, which are crucial for maintaining the security of lightning developers' applications. Given that Hash160 is employed in various other applications, determining its adequacy in this context is imperative. This evaluation is essential not only for the current proposal but also for the broader application of Hash160 in securing blockchain transactions and data.

For those interested in exploring the technical specifics or contributing to the discussion, the draft Bitcoin Improvement Proposal (BIP) provides a comprehensive overview of these proposed changes. The draft BIP can be accessed at, offering valuable insights into the motivations behind these updates and the potential impact on Lightning Symmetry applications and overall blockchain security.