Crypto Sync Issue

Hello, I am interested in encrypting a SLIP link between my PC (running Linux) and my Netcom shell account (running SLIRP). My question has to do with error conditions on the line. If I drop a character or packet, the two sides will loose crypto sync and result in things scrambled from then on. The modems will fix most of the low level problems. However, Murphy's Law has not been repealed. :) Are there any standard methods to provide the SYNC between the sender(encryption) and the receiver(decryption) on an Async connection ? Since Slip uses IP packets, I was planning on an encryption of the data portion of the IP packets (leaving the header alone). Thanks, Tom Rollins <kelso@netcom.com>