Japanese version of the BIFROST guide / Created by @SIPO_Tokyo, thank you: BIFROST｜Cardano SPOs Assume the Security Layer for the BTC Bridge — 10 Days Since Testnet Launch, Entering Final Phase The four-step process outlined by FluidTokens: BTC lock → peg-in → treasury → fBTC mint. The group of Cardano Stake Pool Operators (SPOs) assumes the role of moving BTC within the treasury. BIFROST is a new bridge protocol connecting Bitcoin and Cardano, designed so that Cardano SPOs jointly hold custody of locked BTC. 【Protocol Flow】 - User locks BTC - Creates a peg-in request on Cardano - Network moves BTC to the treasury - fBTC is minted on Cardano upon proof of this transfer fBTC can circulate freely on Cardano and be converted back to BTC via peg-out. 【Development Timeline】 - 2025: Selected for Project Catalyst Fund14 (joint proposal by FluidTokens, ZkFold, and Lantr) - January 22, 2026: Announced entry into the "Final development phase"; GitHub documentation finalized (implementation led by FluidTokens and Lantr) - April 16, 2026, 16:00 UTC: BIFROST publicly launched on BTC testnet - April 25, 2026: Visualized the full peg-in to fBTC mint flow via testnet dApp - June 2026: Catalyst grant development period concludes; discussion begins on incentivization phase design Thus, the testnet has been live for 10 days, and concrete design work on SPO incentivization is just beginning. 【Role of SPOs】 SPOs are not merely delegates—they constitute the security layer of the bridge itself. Their roles are two-fold: - Distributed Key Generation (DKG): SPOs jointly generate a multi-signature key per epoch - FROST threshold signatures: Sign peg-in sweeps, peg-out approvals, and handovers to the next epoch Signatures follow a three-tier cascade structure based on delegated stake weight. A 67% threshold is considered strongest; 51% is standard mode; federation fallback activates only if both fail. Unlike “1 SPO = 1 signature,” signature rights are proportionally allocated according to delegated stake. 【Participation Process】 SPOs must generate their own Secp256k1 Bifrost identification key pair and operate a public endpoint (bifrost_url). By submitting a registration transaction signed with both their cold key (Ed25519) and Bifrost key (Schnorr), they are added to an on-chain whitelist and receive a Bifrost Membership Token minted per pool_id. A minimum delegated stake requirement is also planned. 【Design Positioning】 Since early 2026, multiple hacks have occurred on EVM-based networks using wrapped bridges. BIFROST directly leverages Cardano’s native UTxO model and existing SPO consensus for security, offering an alternative to the dominant paradigm of cross-chain wrapped bridges. The critical question is: Who holds custody? BIFROST distributes custody across Cardano’s validator set—over 3,000 active stake pools. This creates alignment: the same entities securing ADA also secure the bridge’s Bitcoin reserves. 【Status and Next Steps】 The Catalyst Fund14 grant development period continues until June 2026. The proposal states: “Select a small cohort of relevant SPOs to provide feedback and collaboratively shape the incentivization phase.” Design discussions are now entering an active phase. As BIFROST operations may take more than one epoch (5 days), it is designed primarily for large-scale liquidity inflows and outflows, rather than retail use. 【Primary Sources】 BIFROST testnet dApp https://t.co/jGpqe0Ef0t FluidTokens testnet launch announcement (2026-04-14) https://t.co/EnlakY7Trw FluidTokens feature demo tweet (2026-04-25) https://t.co/SoKnlYNXzH ft-bifrost-bridge technical documentation (GitHub) https://t.co/LuerYWRaR7 Bifrost: Bitcoin-Cardano bridge secured by Cardano SPOs (Catalyst Fund14) https://t.co/TDGdKkapp1 BIFROST Bridge Background Explanation (BlockEden, 2026-01-26) https://t.co/LEvFYwMDYM