Merge "Fix Android Keystore key gen for keys requiring user auth." into mnc-dev

            int keySizeBits,

            KeyGenParameterSpec spec) {

        // Constraints:

        // 1. Key must be authorized for signing.

        // 1. Key must be authorized for signing without user authentication.

        // 2. Signature digest must be one of key's authorized digests.

        // 3. For RSA keys, the digest output size must not exceed modulus size minus space needed

        //    for RSA PKCS#1 signature padding (about 29 bytes: minimum 10 bytes of padding + 15--19

            // Key not authorized for signing

            return null;

        }

        if (spec.isUserAuthenticationRequired()) {

            // Key not authorized for use without user authentication

            return null;

        }

        if (!spec.isDigestsSpecified()) {

            // Key not authorized for any digests -- can't sign

            return null;