CHUM RELAY :: signing oracle

  GET  /                     this text
  GET  /pubkey               curve parameters and the public key
  POST /sign     {"message": "<utf-8 string>"}
                             -> {"h": ..., "r": ..., "s": ...}  (decimal strings)
  POST /recover  {"d": "<private key, decimal or 0x hex>"}
                             -> the containment code, if you are right

Every value is a decimal string unless prefixed 0x. Messages are hashed with
SHA-256 and reduced mod n.

Sign whatever you like, as often as you like. The signatures are valid.