I have to build a system that will ultimately print a pass that will allow entrance in a building. The validation of this ticket will be done manually (it can also be automatic but that's not likely at this stage). There is the chance that the person checking does not have access to a computer to validate it.

The idea is that it prints some recognizable pattern for the day.

I started thinking about an hash, but that wouldn't work. So I thought of some symmetric cryptography where the key would generate different patterns. But that doesn't make much sense either.

The only request is that the person that receives the ticket can recognize the pattern. This pattern would change in a daily or weekly basis.

I know these would be subject of reply attacks, but for now this would be enough. If you have suggestions they are welcome.

I have to build a system that will ultimately print a pass allowing access to a building. The validation of this ticket will be done manually (it can also be automatic but that's not likely at this stage). There is the chance that the person checking does not have access to a computer to validate it.

The idea is to print some recognizable pattern for the day.

I started thinking about an hash, but that wouldn't work. So I thought of some symmetric cryptography where the key would generate different patterns. But that doesn't make much sense either.

The only request is that the person that checks the pattern can recognize it. This pattern would change in a daily or weekly basis.

I know these would be subject of replay attacks, but for now this would be enough.