 The individual public keys formula_21 can be made public without breaking security.However, as they are not needed in the public key, it is more practical to keep them secret to minimize its size.To sign a message formula_22 with the Merkle signature scheme, the signer picks a key pair formula_5, signs using the one-time signature scheme, and then adds additional information to prove that it was indeed one of the original key pairs (rather than one newly generated by a forger).