[Timothee]

this is a child pornography cases where mere possession alone is a crime: what if that wasn't the case? What if this was a murder case and the defendant had stored notes about his murder on the computer?

If someone is asked to decrypt their drive for a murder case, could they then invoke the Fifth Amendment on the basis that they might have child pornography? Can the Fifth Amendment protect you on an unrelated crime that you mention without either admitting to it?

[dodedo]

This is covered by 18 USC 6002: http://www.law.cornell.edu/uscode/text/18/6002

In short, a judge will grant a person legal immunity from prosecution. This removes the fifth amendment argument, as you cannot be prosecuted for the child porn, and you can be compelled to testify.

For example, an accomplice to a crime might be offered immunity -- after which the accomplice cannot refuse to testify under the fifth amendment. Remember, the fifth only guarantees that you will not be compelled to serve as a witness against yourself -- it does NOT grant you the right to remain silent at all times, contrary to popular belief.

[gonehome]

What if the decryption key is "I am guilty of the murder", would it then be protected since the act of revealing it would be self incriminating?

[mfjordvald]

How would that work? If I write "I just killed a child" here it doesn't mean I actually did that. Similarly. if I used a decryption key "I am guilty of the murder" then it still does not mean I'm guilty of any murder, just that I have a poor sense of humour and used an odd encryption key.

[pantaloons]

That encryption key wouldn't provide proof, but there are many that would. Trivially a sufficiently long key could embed a video of the murder.

[Dylan16807]

And it would be trivially impossible to memorize.