Chain-Key Cryptography

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Explain chain-key cryptography from a developer perspective. Cover threshold ECDSA (Bitcoin/Ethereum signing), threshold Schnorr (Bitcoin Taproot), BLS signatures (consensus and certification), key management across subnets, and chain evolution technology (subnet membership changes without downtime). Focus on what developers can do with chain-key: sign for other chains, verify responses, build cross-chain apps.

• Portal: chain-key sections (scattered across multiple files)
• Learn Hub: Chain-Key Cryptography, Subnet Keys and Subnet Signatures, Chain-Key Signatures, Chain Evolution

• concepts/chain-fusion — chain-key enables chain fusion
• guides/chain-fusion/bitcoin — ECDSA/Schnorr in practice
• guides/chain-fusion/ethereum — ECDSA in practice
• concepts/vetkeys — related cryptographic primitive