system and method for determining the updating time by a server presumed to have a correct time and a client needing a correct time . the server can first transmit an unencrypted signal , which may be signed or unsigned . the server can then later encrypt or sign the same packet it transmitted with a private key and transmit it to the client . after the client receives the unencrypted packet , the client can compute a time difference . however the client doesn &# 39 ; t update its time until a follow - up packet is received from the server . if encrypted , the packet is decoded with the server &# 39 ; s public key , and the decoded packet is shown identical to the received packet and that the identification bits are the same .