Int saltLength = 32 // bytes should be the same size * Store these things on disk used to derive key later: */
If you're using a password to derive a key, follow Nikolay Elenkov's excellent tutorial with the caveat that a good rule of thumb is the salt size should be the same size as the key output.SecretKey key = new SecretKeySpec(keyBytes, "AES") You can get a SecretKey for AES usage from the bytes by doing: If you're reading an AES key from disk, just store the actual key and don't go through this weird dance.Keys can be derived in the following way: There’s also aįull example, including a helper class to use the deprecated SHA1PRNGįunctionality, with the sole purpose of decrypting data that would be otherwise
In the following, we explain how to derive keys correctly, and how to decryptĭata that has been encrypted using an insecure key. “predictable and cryptographically weak”). "random" output bytes for the key (where “random” in this sentence means Was used to derive a key by supplying a password as a seed, and then using the Made it deterministic if setSeed() was called before obtaining output. The implementation of SHA1PRNG had a bug that However, given its continued use,Ī common but incorrect usage of this provider was to derive keys for encryptionīy using a password as a seed. We’d previously covered the issues with using SecureRandom for key derivation aĬryptography to Store Credentials Safely. Implementation of the SHA1PRNG algorithm and the Crypto provider altogether.
Returning 0s, and that the bias worsens depending on the seed.Īs a result, in Android N we are deprecating the States that the “random” sequence, considered in binary form, is biased towards With PHP and Debian OpenSSL,Section 8.1, by Yongge Want and Tony Nicol, Statistical distance based testing of pseudo random sequences and experiments For readers interested in the details, On The problem is that the SHA1PRNG algorithm is notĬryptographically strong. This provider only provided an implementation of the algorithm “SHA1PRNG” for Unfortunately, many apps depend on the now removed “Crypto” provider for an The Java Cryptography Extension (JCE) APIs specifying a provider should only beĭone if the provider is included in the application or if the application isĪble to deal with a possible ProviderNotFoundException. On Android, we don’t recommend specifying the provider. SomeClass.getInstance("SomeAlgorithm", "SomeProvider") Ĭipher.getInstance(“AES/CBC/PKCS5PADDING”) The Java Cryptography Architecture allows developers to create an instance of a class like a cipher, or a pseudo-random number generator, using calls like: Provider, you must start using a real key derivation function and possibly re-encrypt your data. If your Android app derives keys using the SHA1PRNG algorithm from the Crypto