Samsung's vaunted Knox security got it a US government contract. . . and two weeks later it was discovered that Samsung was keeping the KEY to access to Knox in an insecure Library in an unencrypted text format that anyone could easily find. LOL! It was as secure as wet tissue paper!
Apple's keys are kept in a HASH inside it's Secure Element which is part of the PROCESSOR and the hash has to be recalculated each time it is entered and compared to the hash that is stored in the Secure Element which cannot be accessed from outside the iPhone, nor is it ever transmitted from the iPhone. That hash then unlocks the phone, but the key itself is entangled with the 256 bit UUID of the iPhone itself to use as a KEY to encrypt the data contents on the iPhone. Apple itself never gets that hash and cannot decrypt your data. They ARE secure.
Android phones are not. . . even Samsung phones with Knox Security. Perhaps Samsung has solved that problem with the Samsung Galaxy S6.