Bitcoin Message Signing Two specifications: - BIP137 (Hourglass) — legacy. Works only for P2PKH (uncompressed or compressed). Output: 65-byte recoverable ECDSA + Base64. - BIP322 (modern) — works for any output type (P2PKH, P2WPKH, P2WSH, P2TR, even script-only). Output: a virtual PSBT-like signature. BIP137 (legacy) Verify: recover pubkey from signature, derive P2PKH address, compare. Limitations : - Only P2PKH. Cannot prove ownership of a SegWit / Taproot address. - Wallets don't always agree on the prefix (some include trailing newline, others don't). - Recoverable ECDSA implies pubkey isn…