Actually, you are incorrect.
The 5th absolutely protects the "contents of one's mind". The Supreme often uses those exact words in many cases affirming the notion. In fact, one common analogy the court uses in deciding these issues is that the government can force a suspect to produce the key to a safe, but it cannot force him/her to produce a combination for a safe.
The 5th does protect against coerced testimony, and that includes passwords or knowledge of physical evidence. However, once the government knows that physical evidence exists and is in the possession or under the control of the suspect they can compel the suspect to produce the evidence, whether that evidence be business records, personal papers or computer data. So while the suspect cannot be compelled to reveal his password, if the government knows an encrypted drive contains incriminating evidence it can compel him/her to produce the unencrypted data. That is why the suspect are not ordered to reveal the password, but to unlock the data for the police.
One key distinction here is that the government must have ‘reasonably particularity’ concerning the evidence it requests. They cannot merely suspect the evidence may exist. Cases where defendants are compelled to produce unencrypted drives usually have other factors such as U.S. v. Friscou where the government had recordings of the defendant talking about the incriminating contents of the encrypted data. Or, in re Boucher where police saw the unencrypted content of a laptop that was turned on, but then lost access when it was powered down.
In the safe analogy the police cannot compel a suspect to produce a combination, but if they have sufficient reason to believe the safe contains a incriminating accounting ledger, they can compel the suspect to open it and produce the ledger.