Most existing tamper-indicating seals operate under the same basic principle. Once the seal is opened, information that the seal has indeed been unsealed is stored in or on the security seals until such time as the seal can be inspected. With inexpensive passive (mechanical) seals, this alarm condition is typically indicated by destruction, damage, or modification to the seal body. With active (electronic) seals, the alarm condition is usually stored electronically or magnetically within the seal, or shown on an electronic display. The fundamental problem with this approach is that an adversary can usually erase the alarm condition with little difficulty. With passive seals, this may mean repairing or cosmetically hiding the destruction, damage, or modification that occurred while opening the seal. With electronic seals, it means attacking/erasing a memory location, or tampering with the electronic display. There are many other types of attacks, but few are as easy to implement, nor as likely to go undetected by the seal user.
