A teenager has been jailed for 16 weeks after he refused to give police the password to his computer.
Oliver Drage, 19, of Liverpool, was arrested in May 2009 by police tackling child sexual exploitation.
Police seized his computer but could not access material on it as it had a 50-character encryption password.
Drage was convicted of failing to disclose an encryption key in September. He was sentenced at Preston Crown Court on Monday.
Drage was arrested when he was living in Freckleton, Lancashire, but later moved to Liverpool.
He was formally asked to disclose his password but failed to do so, which is an offence under the Regulation of Investigatory Powers Act 2000, police said.
Officers are still trying to crack the code on the computer to examine its contents.
Det Sgt Neil Fowler, of Lancashire police, said: "Drage was previously of good character so the immediate custodial sentence handed down by the judge in this case shows just how seriously the courts take this kind of offence.
"Computer systems are constantly advancing and the legislation used here was specifically brought in to deal with those who are using the internet to commit crime.
"It sends a robust message out to those intent on trying to mask their online criminal activities that they will be taken before the courts with the ultimate sanction, as in this case, being a custodial sentence."
(applied to political protests as well? - fc)