Touch ID is Apple's name for its fingerprint sensor technology in the iPhone 5s home button, an alternative to typing in a lock screen passcode. See also: Touch ID on TheiPhoneWiki.
All fingerprint information is encrypted and stored in the A7 chip. TouchID stores "mathematical representation" of fingerprints.
The iPhone 5s has a security architecture called Secure Enclave within the A7 chip, which protects and verifies fingerprint matches. Apple said the Secure Enclave is "walled off from the rest of A7 and as well as the rest of iOS", meaning only Touch ID has access to fingerprint data.
TouchID has 4 header files (which can all be found at developer.limneos.net):
PSBiometricIdentity.h SBUIBiometricEventMonitor.h SBUIBiometricEventObserver.h BiometricKitDelegate.h
The main class is BiometricKit, which is a singleton class (+manager).
PSBiometricIdentity.h is responsible for the settings of TouchID, which can be found in Settings > General > Touch ID & Passcode > Touch ID. The two SpringBoardUIServices headers are responsible for scanning and detecting the finger on the lock screen; they use the delegate methods to, for example, match the finger such as in the
If you log the argument of that method, you will get something around the lines of:
-[<SBUIBiometricEventMonitor: 0x17867c3c0> matchResult:<BiometricKitIdentity: 0x1782562f0>] . That
<BiometricKitIdentity: 0x1782562f0> is the name of the finger that was just scanned and verified. We know from Apple that Touch ID is stored on the A7 processor chip inside the 5s in a secure enclave. What do we not know? How much storage is their in this secure enclave? Is it variable?