The government faces criticism over plans to give police powers to make suspects produce readable copies of encrypted computer evidence.
The police say the powers are needed because criminals are increasingly using encryption to hide evidence.
They estimate that currently there are 30 cases in which encrypted evidence had stumped investigators.
But some peers, academics and cryptographers say the plans are flawed and risk being abused.
The plans to let police demand decryption are part of the controversial Regulation of Investigatory Powers Act (RIPA) that came into force in 2000.
Part III of RIPA gives law enforcement agencies the decryption powers and, provided some conditions are met, makes it a serious offence to refuse to turn scrambled files into an “intelligible” form. Those refusing could see their sentence increased as a result.
Professor Douwe Korff, said there was a real question as to whether the powers undermined the presumption of innocence that human rights legislation enshrines. The code of conduct had to be beefed up, he said, to ensure high standards protected fundamental rights.
Lord Phillips of Sudbury described RIPA as a “hair-raising” piece of legislation and expressed reservations about the effect the powers being given to police would have.
“You do not secure the liberty of our country and value of our democracy by undermining them,” he said. “That’s the road to hell.”