Truecrypt has hidden volumes. There's also https://en.wikipedia.org/wiki/Rubberhose_(file_system) https://en.wikipedia.org/wiki/Rubberhose_(file_system) and ot

Truecrypt has hidden volumes. There's also https://en.wikipedia.org/wiki/Rubberhose_(file_system) https://en.wikipedia.org/wiki/Rubberhose_(file_system) and others: https://en.wikipedia.org/wiki/Deniable_encryption https://en.wikipedia.org/wiki/Deniable_encryption Same general principle, you allegedly can't prove the hidden volumes exist unless you have the decryption key.