InputStream decode()

in src/main/java/org/apache/commons/compress/archivers/sevenz/AES256SHA256Decoder.java [92:167]
70 lines of code
9 McCabe index (conditional complexity)

    InputStream decode(final String archiveName, final InputStream in, final long uncompressedLength,
            final Coder coder, final byte[] passwordBytes, final int maxMemoryLimitInKb) {
        return new InputStream() {
            private boolean isInitialized;
            private CipherInputStream cipherInputStream;

            @Override
            public void close() throws IOException {
                if (cipherInputStream != null) {
                    cipherInputStream.close();
                }
            }

            private CipherInputStream init() throws IOException {
                if (isInitialized) {
                    return cipherInputStream;
                }
                if (coder.properties == null) {
                    throw new IOException("Missing AES256 properties in " + archiveName);
                }
                if (coder.properties.length < 2) {
                    throw new IOException("AES256 properties too short in " + archiveName);
                }
                final int byte0 = 0xff & coder.properties[0];
                final int numCyclesPower = byte0 & 0x3f;
                final int byte1 = 0xff & coder.properties[1];
                final int ivSize = ((byte0 >> 6) & 1) + (byte1 & 0x0f);
                final int saltSize = ((byte0 >> 7) & 1) + (byte1 >> 4);
                if (2 + saltSize + ivSize > coder.properties.length) {
                    throw new IOException("Salt size + IV size too long in " + archiveName);
                }
                final byte[] salt = new byte[saltSize];
                System.arraycopy(coder.properties, 2, salt, 0, saltSize);
                final byte[] iv = new byte[16];
                System.arraycopy(coder.properties, 2 + saltSize, iv, 0, ivSize);

                if (passwordBytes == null) {
                    throw new PasswordRequiredException(archiveName);
                }
                final byte[] aesKeyBytes;
                if (numCyclesPower == 0x3f) {
                    aesKeyBytes = new byte[32];
                    System.arraycopy(salt, 0, aesKeyBytes, 0, saltSize);
                    System.arraycopy(passwordBytes, 0, aesKeyBytes, saltSize,
                                     Math.min(passwordBytes.length, aesKeyBytes.length - saltSize));
                } else {
                    aesKeyBytes = sha256Password(passwordBytes, numCyclesPower, salt);
                }

                final SecretKey aesKey = AES256Options.newSecretKeySpec(aesKeyBytes);
                try {
                    final Cipher cipher = Cipher.getInstance(AES256Options.TRANSFORMATION);
                    cipher.init(Cipher.DECRYPT_MODE, aesKey, new IvParameterSpec(iv));
                    cipherInputStream = new CipherInputStream(in, cipher);
                    isInitialized = true;
                    return cipherInputStream;
                } catch (final GeneralSecurityException generalSecurityException) {
                    throw new IllegalStateException(
                        "Decryption error (do you have the JCE Unlimited Strength Jurisdiction Policy Files installed?)",
                        generalSecurityException);
                    }
            }

            @SuppressWarnings("resource") // Closed in close()
            @Override
            public int read() throws IOException {
                return init().read();
            }

            @SuppressWarnings("resource") // Closed in close()
            @Override
            public int read(final byte[] b, final int off, final int len) throws IOException {
                return init().read(b, off, len);
            }
        };
    }