I have sensitive data on my computers and phones. I use Trycrypt's plausible deniability system on my computers. When law enforcement/border patrol or my spouse asks for access I type in the password for the decoy system. I need this badly for my phone. Does anyone know how to install a plausible deniability system for a smart phone?
Plausible deniability is really more of a political or social tactic than a security measure. As a tactic, plausible deniabilty seeks to prevent the disclosure of information by presenting an argument about the knowledge a given individual has. This is a second order game, at least one level removed from direct protection of information.
An Example: Alice is a ruthless criminal. Bob and Don are her criminal associates. On Monday Bob is a witness to one of Alice's crimes. On Tuesday Alice and Bob have an argument. On Wednesday Bob meets with Carol and tells Carol some confidential information about Alice's activity on Monday that could be used to arrest and prosecute Alice for her crimes. On Thursday, the next time Bob and Alice meet, Alice asks Bob who he met with on Wednesday. Bob claims he met with Don, another of Alice's associates.
By naming Don instead of Carol, Bob has provided Carol plausible deniability about the information he provided to her.
If at this point Alice decided to kill anyone with information about her criminal activity on Monday, she might decided to kill Bob and Don.
How is this relevant to Truecrypt?
Truecrypt is trying to play a similar game. Rather than try to disguise the fact that a user has encrypted some information. They are giving the user two shells under which to hide information. Under shell A is confidential information the user wishes to keep private. Under shell B is information the user is willing to disclose if that disclosure keeps the information under shell A confidential.
Now the content of the information under shell B ("the decoy") is important. If nothing is kept there except freely available public domain information. The plausible deniability will not work. It will not convince anyone (law enforcement, border patrol, or spouse) that the user went to some effort to protect the information. And since the fact that Truecrypt offers 'Plausible deniability' as a feature is well known, most professional phone inspectors will know that what you have presented is a 'decoy'.
Further notice that this tactic depends entirely on the inspector deciding that it is not plausible you have the information they are seeking and as a consequence do not pursue them further.
Lets go back to the criminal Alice from the first example. Lets say she decides not to believe Bob about who Bob met with on Wednesday. Suppose that Alice knows that Bob is friends with Carol and decided to kill Carol just in case Bob told Carol the incriminating information. At this point the plausible deniability tactic's value goes to zero as the recipient of the tactic uses possible instead of plausible as the discriminator for the decision to take action.
That means that this tactic only works against those whose decisions for action are evaluated based on plausible evidence. And most persons who are not under the instruction of a magistrate have a much lower threshold for suspecting guilt.
As for technical solutions, the only thing that comes to mind right off is to use a rooted Android that has been set up for dual/multiple booting. Only a few models of Android phones support this; consult an Android forum for further details.
Now, if you need to protect data from your spouse, it's time to take a long hard look at (1) your marriage and (2) what you're doing. Unfortunately, we probably can't help you with either of those.
If you have an Android Smartphone, you can try this:
You can have two Passwords:
It also offers Optional file Encryption (to avoid other File Managers from reading these Files)
I think this is a Smart Solution!
Otherwise, you can check if your phone supports Truecrypt! (Or a similar Program)
The usual method to gain plausible deniability w.r.t. phones is to have two; a clean phone you show to the cops and your wife, and a dirty phone you show no-one. There are of course considerable practical difficulties with this.
Also, from the scenarios you give, I'd suggest you are making the common security error of over-reliance on technical controls. Re-run the risk analysis and go broader in the treatments you consider. Remember, where practical, risk avoidance is almost always a better treatment approach than risk control - why have sensitive data on your phone in the first place?