SwiftSync - smarter synchronization with hints

In a recent exchange on the Bitcoin Development Mailing List, a novel approach to transaction output handling was proposed, suggesting the possibility of bypassing traditional hashing techniques. This suggestion posits that by directly using the combination of transaction ID and output index (txid:vout), which occupies 36 bytes, one could effectively manage these outputs as if they were results of a 288-bit hash function. This method hinges on the blend of the original data with a salt, aiming to maintain the integrity of transactions without the need for conventional hashing.

However, this proposition is not without its challenges. Concerns were raised about the potential for manipulation, such as the substitution of output pairs (e.g., replacing "(txid:1) + (txid:4)" with "(txid:2) + (txid:3)"), which underscores the need for a robust mechanism to safeguard against such vulnerabilities. Additionally, the discussion highlighted certain transaction outputs that can be predetermined in terms of how they will be hashed, suggesting the use of "hashPrevouts" as a possible optimization. This could expedite processing for transactions that spend coins previously involved in other transactions, leveraging pre-hashed data for efficiency gains.

Despite these innovative ideas, the conversation acknowledged the difficulties in implementing such optimizations within the current frameworks, as exemplified by BIP-143. The dialogue suggests a forward-looking perspective, advocating for the design of future protocols in a manner that accommodates these types of enhancements, potentially paving the way for more efficient and secure transaction processing in blockchain technologies.