Android KeyStore is a secure container for storing key materials, in particular it prevents key materials extraction, i.e. when the application
process is compromised, the attacker cannot extract keys but may still be able to use them. It’s possible to enable an Android security feature, user
authentication, to restrict usage of keys to only authenticated users. The lock screen has to be unlocked with defined credentials
(pattern/PIN/password, biometric).
Ask Yourself Whether
- The application requires prohibiting the use of keys in case of compromise of the application process.
- The key material is used in the context of a highly sensitive application like a e-banking mobile app.
There is a risk if you answered yes to any of those questions.
Recommended Secure Coding Practices
It’s recommended to enable user authentication (by setting setUserAuthenticationRequired to true during key generation)
to use keys for a limited duration of time (by setting appropriate values to setUserAuthenticationValidityDurationSeconds), after which
the user must re-authenticate.
Sensitive Code Example
Any user can use the key:
KeyGenerator keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");
KeyGenParameterSpec builder = new KeyGenParameterSpec.Builder("test_secret_key_noncompliant", KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT) // Noncompliant
.setBlockModes(KeyProperties.BLOCK_MODE_GCM)
.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
.build();
keyGenerator.init(builder);
Compliant Solution
The use of the key is limited to authenticated users (for a duration of time defined to 60 seconds):
KeyGenerator keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");
KeyGenParameterSpec builder = new KeyGenParameterSpec.Builder("test_secret_key", KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
.setBlockModes(KeyProperties.BLOCK_MODE_GCM)
.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
.setUserAuthenticationRequired(true)
.setUserAuthenticationParameters (60, KeyProperties.AUTH_DEVICE_CREDENTIAL)
.build();
keyGenerator.init(builder)
See
