[작업로그] 서명 생성/검증

#1. 서명 생성

• [param]
• algo: 
• privKey:  the private key of the identity whose signature is going to be generated.

• [code]

  Signature signer = Signature.getInstance(algo, "BC");
  signer.initSign(this.privKey);
  signer.update(plainText);
  return signer.sign();

#2. 서명 검증

• [param] 
• algo : the name of the algorithm requested.
• pubKey: the public key of the identity whose signature is going to be verified.
• plainText
• signed: the signature bytes to be verified.

• [code]

  Signature signer = Signature.getInstance(algo, "BC");
  signer.initVerify(pubKey);
  signer.update(plainText);
  return signer.verify(signed);