It's all very confusing so no point rushing to any conclusions.

The Register writes:

"the government says that Miranda was actually carrying a piece of paper with a decryption password written on it. This allowed the police to read at least some of the files he was carrying." [1]

While Greenwald just tweeted:

"Anyone claiming that David Miranda was carrying a password that allowed access to documents is lying. UK itself says they can't access them."[2]

[1] http://www.theregister.co.uk/2013/08/30/snowden_journos_boyf...

[2] https://twitter.com/ggreenwald/status/373451644794449922