code: function(pk, challenge, signature) {
      var pem = "-----BEGIN RSA PUBLIC KEY-----\n" 
          + pk.replace(/(.{64})/g, "$1\n")
          + "\n-----END RSA PUBLIC KEY-----";
  
      var rsa = crypto.createVerify("RSA-SHA256");
      rsa.update(new Buffer(challenge, "base64"));
      if(rsa.verify(pem, signature, "base64"))
      {
          return { result : true };
      }
      else {
          return { result : false };
      }
  }
docs: Verify signature
  
  @param {Object} pk The public key
  @param {Object} challenge The challenge
  @param {Object} signature The signed challenge
  @api private