Re: "Self-Incrimination"
Your entire argument is a disaster.
"The password he was required to give is, in itself, not evidence against himself"
First of all, what if his password was "I_confess_to_the_crimes_of_xyz"? Wouldn't the requirement for him to give up his password be in direct conflict with his right not to incriminate himself? Please don't say "Well, he would be stupid to do that" because fundamental rights belong to everyone, not just the intelligent.
Secondly, other than name, date of birth, and address, ANY AND ALL information that you give to the police is potentially incriminating. The police can demand to know what your favorite color is, and you are STILL protected from having to tell them this. That's because police can, and do, twist anything you say to make you appear as guilty as possible.
That is why nobody can ever be "required" to give "innocent" information to the police.
"Additionally, as he had already been convicted of a serious crime, there was probable cause "
No. Wrong. A criminal record NEVER constitutes probable cause. If it did, the police would be entitled to search his car, search his home, etc etc, every day for the rest of his life.
"As he had already been convicted of a crime, the right not to incriminate oneself becomes moot: as he is no longer capable of incriminating himself as he has been found guilty. "
It pains me to have to explain how wrong you are on this. NO, A CRIMINAL RECORD DOES NOT REVOKE YOUR RIGHT NOT TO INCRIMINATE YOURSELF IN FUTURE CRIMES. THAT I NEED TO EXPLAIN THIS TO YOU IS DEEPLY DISTURBING.
"but again, concealment of evidence is taken more seriously and the right to silence does not protect the concealer."
You are just 100 percent dead wrong. Nobody on this planet is legally required to provide evidence that might be used against them. This is so basic it almost gives me a headache.
"(Somewhat analogous are court decisions in the US stating that income must be declared even if the result of criminality and a failure to declare such income renders one liable for imprisonment for income tax evasion."
And there's a very good argument to be made, a slam-dunk case even, that the laws in the tax code are unconstitutional. The only reason the IRS can get away with this is because filing an income tax return is officially declared a voluntary act, not compulsory. However, the law states that you MUST volunteer to submit your 100% completely non-compulsory income tax return. If you fail to volunteer, you're guilty of tax evasion.
Pointing to the Internal Revenue Service as a role model of legality is ridiculous.