Class AesAlgorithm

impl/src/main/java/io/jsonwebtoken/impl/security/AesAlgorithm.java:42–210

@since 0.12.0

 * @since 0.12.0
 */
abstract class AesAlgorithm extends CryptoAlgorithm implements KeyBuilderSupplier<SecretKey, SecretKeyBuilder>, KeyLengthSupplier {

    protected static final String KEY_ALG_NAME = "AES";
    protected static final int BLOCK_SIZE = 128;
    protected static final int BLOCK_BYTE_SIZE = BLOCK_SIZE / Byte.SIZE;
    protected static final int GCM_IV_SIZE = 96; // https://tools.ietf.org/html/rfc7518#section-5.3
    //protected static final int GCM_IV_BYTE_SIZE = GCM_IV_SIZE / Byte.SIZE;
    protected static final String DECRYPT_NO_IV = "This algorithm implementation rejects decryption " +
            "requests that do not include initialization vectors. AES ciphertext without an IV is weak and " +
            "susceptible to attack.";

    protected final int keyBitLength;
    protected final int ivBitLength;
    protected final int tagBitLength;
    protected final boolean gcm;

    /**
     * Ensures {@code keyBitLength is a valid AES key length}
     * @param keyBitLength the key length (in bits) to check
     * @since 0.12.4
     */
    static void assertKeyBitLength(int keyBitLength) {
        if (keyBitLength == 128 || keyBitLength == 192 || keyBitLength == 256) return; // valid
        String msg = "Invalid AES key length: " + Bytes.bitsMsg(keyBitLength) + ". AES only supports " +
                "128, 192, or 256 bit keys.";
        throw new IllegalArgumentException(msg);
    }

    static SecretKey keyFor(byte[] bytes) {
        int bitlen = (int) Bytes.bitLength(bytes);
        assertKeyBitLength(bitlen);
        return new SecretKeySpec(bytes, KEY_ALG_NAME);
    }

    AesAlgorithm(String id, final String jcaTransformation, int keyBitLength) {
        super(id, jcaTransformation);
        assertKeyBitLength(keyBitLength);
        this.keyBitLength = keyBitLength;
        this.gcm = jcaTransformation.startsWith("AES/GCM");
        this.ivBitLength = jcaTransformation.equals("AESWrap") ? 0 : (this.gcm ? GCM_IV_SIZE : BLOCK_SIZE);
        // https://tools.ietf.org/html/rfc7518#section-5.2.3 through https://tools.ietf.org/html/rfc7518#section-5.3 :
        this.tagBitLength = this.gcm ? BLOCK_SIZE : this.keyBitLength;
    }

    @Override
    public int getKeyBitLength() {
        return this.keyBitLength;
    }

    @Override
    public SecretKeyBuilder key() {
        return new DefaultSecretKeyBuilder(KEY_ALG_NAME, getKeyBitLength());
    }

    protected SecretKey assertKey(SecretKey key) {
        Assert.notNull(key, "Request key cannot be null.");
        validateLengthIfPossible(key);
        return key;