(0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141-0xda809197a6d5a2dccc83bb104d1e6b4ebbefc77a1982a790f16687783ee74720).to_s 16

=> "257f6e68592a5d23337c44efb2e194affebf156c95c5f8aace6bd714914efa21"

(0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141はsecp256k1のn)