ChaCha20Cipher.java

/*
 * Copyright (c) 2018, 2021, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package com.sun.crypto.provider;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.security.*;
import java.security.spec.AlgorithmParameterSpec;
import java.util.Arrays;
import java.util.Objects;
import javax.crypto.*;
import javax.crypto.spec.ChaCha20ParameterSpec;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import sun.security.util.DerValue;

/**
 * Implementation of the ChaCha20 cipher, as described in RFC 7539.
 *
 * @since 11
 */
abstract class ChaCha20Cipher extends CipherSpi {
    // Mode constants
    private static final int MODE_NONE = 0;
    private static final int MODE_AEAD = 1;

    // Constants used in setting up the initial state
    private static final int STATE_CONST_0 = 0x61707865;
    private static final int STATE_CONST_1 = 0x3320646e;
    private static final int STATE_CONST_2 = 0x79622d32;
    private static final int STATE_CONST_3 = 0x6b206574;

    // The keystream block size in bytes and as integers
    private static final int KEYSTREAM_SIZE = 64;
    private static final int KS_SIZE_INTS = KEYSTREAM_SIZE / Integer.BYTES;
    private static final int CIPHERBUF_BASE = 1024;

    // The initialization state of the cipher
    private boolean initialized;

    // The mode of operation for this object
    protected int mode;

    // The direction (encrypt vs. decrypt) for the data flow
    private int direction;

    // Has all AAD data been provided (i.e. have we called our first update)
    private boolean aadDone = false;

    // The key's encoding in bytes for this object
    private byte[] keyBytes;

    // The nonce used for this object
    private byte[] nonce;

    // The counter
    private static final long MAX_UINT32 = 0x00000000FFFFFFFFL;
    private long finalCounterValue;
    private long counter;

    // Two arrays, both implemented as 16-element integer arrays:
    // The base state, created at initialization time, and a working
    // state which is a clone of the start state, and is then modified
    // with the counter and the ChaCha20 block function.
    private final int[] startState = new int[KS_SIZE_INTS];
    private final byte[] keyStream = new byte[KEYSTREAM_SIZE];

    // The offset into the current keystream
    private int keyStrOffset;

    // AEAD-related fields and constants
    private static final int TAG_LENGTH = 16;
    private long aadLen;
    private long dataLen;

    // Have a buffer of zero padding that can be read all or in part
    // by the authenticator.
    private static final byte[] padBuf = new byte[TAG_LENGTH];

    // Create a buffer for holding the AAD and Ciphertext lengths
    private final byte[] lenBuf = new byte[TAG_LENGTH];

    // The authenticator (Poly1305) when running in AEAD mode
    protected String authAlgName;
    private Poly1305 authenticator;

    // The underlying engine for doing the ChaCha20/Poly1305 work
    private ChaChaEngine engine;

    // Use this VarHandle for converting the state elements into little-endian
    // integer values for the ChaCha20 block function.
    private static final VarHandle asIntLittleEndian =
            MethodHandles.byteArrayViewVarHandle(int[].class,
                    ByteOrder.LITTLE_ENDIAN);

    // Use this VarHandle for converting the AAD and data lengths into
    // little-endian long values for AEAD tag computations.
    private static final VarHandle asLongLittleEndian =
            MethodHandles.byteArrayViewVarHandle(long[].class,
                    ByteOrder.LITTLE_ENDIAN);

    // Use this for pulling in 8 bytes at a time as longs for XOR operations
    private static final VarHandle asLongView =
            MethodHandles.byteArrayViewVarHandle(long[].class,
                    ByteOrder.nativeOrder());

    /**
     * Default constructor.
     */
    protected ChaCha20Cipher() { }

    /**
     * Set the mode of operation.  Since this is a stream cipher, there
     * is no mode of operation in the block-cipher sense of things.  The
     * protected {@code mode} field will only accept a value of {@code None}
     * (case-insensitive).
     *
     * @param mode The mode value
     *
     * @throws NoSuchAlgorithmException if a mode of operation besides
     *      {@code None} is provided.
     */
    @Override
    protected void engineSetMode(String mode) throws NoSuchAlgorithmException {
        if (mode.equalsIgnoreCase("None") == false) {
            throw new NoSuchAlgorithmException("Mode must be None");
        }
    }

    /**
     * Set the padding scheme.  Padding schemes do not make sense with stream
     * ciphers, but allow {@code NoPadding}.  See JCE spec.
     *
     * @param padding The padding type.  The only allowed value is
     *      {@code NoPadding} case insensitive).
     *
     * @throws NoSuchPaddingException if a padding scheme besides
     *      {@code NoPadding} is provided.
     */
    @Override
    protected void engineSetPadding(String padding)
            throws NoSuchPaddingException {
        if (padding.equalsIgnoreCase("NoPadding") == false) {
            throw new NoSuchPaddingException("Padding must be NoPadding");
        }
    }

    /**
     * Returns the block size.  For a stream cipher like ChaCha20, this
     * value will always be zero.
     *
     * @return This method always returns 0.  See the JCE Specification.
     */
    @Override
    protected int engineGetBlockSize() {
        return 0;
    }

    /**
     * Get the output size required to hold the result of the next update or
     * doFinal operation.  In simple stream-cipher
     * mode, the output size will equal the input size.  For ChaCha20-Poly1305
     * for encryption the output size will be the sum of the input length
     * and tag length.  For decryption, the output size will be  the input
     * length plus any previously unprocessed data minus the tag
     * length, minimum zero.
     *
     * @param inputLen the length in bytes of the input
     *
     * @return the output length in bytes.
     */
    @Override
    protected int engineGetOutputSize(int inputLen) {
        return engine.getOutputSize(inputLen, true);
    }

    /**
     * Get the nonce value used.
     *
     * @return the nonce bytes.  For ChaCha20 this will be a 12-byte value.
     */
    @Override
    protected byte[] engineGetIV() {
        return (nonce != null) ? nonce.clone() : null;
    }

    /**
     * Get the algorithm parameters for this cipher.  For the ChaCha20
     * cipher, this will always return {@code null} as there currently is
     * no {@code AlgorithmParameters} implementation for ChaCha20.  For
     * ChaCha20-Poly1305, a {@code ChaCha20Poly1305Parameters} object will be
     * created and initialized with the configured nonce value and returned
     * to the caller.
     *
     * @return a {@code null} value if the ChaCha20 cipher is used (mode is
     * MODE_NONE), or a {@code ChaCha20Poly1305Parameters} object containing
     * the nonce if the mode is MODE_AEAD.
     */
    @Override
    protected AlgorithmParameters engineGetParameters() {
        AlgorithmParameters params = null;
        if (mode == MODE_AEAD) {
            // In a pre-initialized state or any state without a nonce value
            // this call should cause a random nonce to be generated, but
            // not attached to the object.
            byte[] nonceData = (initialized || nonce != null) ? nonce :
                    createRandomNonce(null);
            try {
                // Place the 12-byte nonce into a DER-encoded OCTET_STRING
                params = AlgorithmParameters.getInstance("ChaCha20-Poly1305");
                params.init((new DerValue(
                        DerValue.tag_OctetString, nonceData).toByteArray()));
            } catch (NoSuchAlgorithmException | IOException exc) {
                throw new RuntimeException(exc);
            }
        }

        return params;
    }

    /**
     * Initialize the engine using a key and secure random implementation.  If
     * a SecureRandom object is provided it will be used to create a random
     * nonce value.  If the {@code random} parameter is null an internal
     * secure random source will be used to create the random nonce.
     * The counter value will be set to 1.
     *
     * @param opmode the type of operation to do.  This value may not be
     *      {@code Cipher.DECRYPT_MODE} or {@code Cipher.UNWRAP_MODE} mode
     *      because it must generate random parameters like the nonce.
     * @param key a 256-bit key suitable for ChaCha20
     * @param random a {@code SecureRandom} implementation used to create the
     *      random nonce.  If {@code null} is used for the random object,
     *      then an internal secure random source will be used to create the
     *      nonce.
     *
     * @throws UnsupportedOperationException if the mode of operation
     *      is {@code Cipher.WRAP_MODE} or {@code Cipher.UNWRAP_MODE}
     *      (currently unsupported).
     * @throws InvalidKeyException if the key is of the wrong type or is
     *      not 256-bits in length.  This will also be thrown if the opmode
     *      parameter is {@code Cipher.DECRYPT_MODE}.
     *      {@code Cipher.UNWRAP_MODE} would normally be disallowed in this
     *      context but it is preempted by the UOE case above.
     */
    @Override
    protected void engineInit(int opmode, Key key, SecureRandom random)
            throws InvalidKeyException {
        if (opmode != Cipher.DECRYPT_MODE) {
            byte[] newNonce = createRandomNonce(random);
            counter = 1;
            init(opmode, key, newNonce);
        } else {
            throw new InvalidKeyException("Default parameter generation " +
                "disallowed in DECRYPT and UNWRAP modes");
        }
    }

    /**
     * Initialize the engine using a key and secure random implementation.
     *
     * @param opmode the type of operation to do.  This value must be either
     *      {@code Cipher.ENCRYPT_MODE} or {@code Cipher.DECRYPT_MODE}
     * @param key a 256-bit key suitable for ChaCha20
     * @param params a {@code ChaCha20ParameterSpec} that will provide
     *      the nonce and initial block counter value.
     * @param random a {@code SecureRandom} implementation, this parameter
     *      is not used in this form of the initializer.
     *
     * @throws UnsupportedOperationException if the mode of operation
     *      is {@code Cipher.WRAP_MODE} or {@code Cipher.UNWRAP_MODE}
     *      (currently unsupported).
     * @throws InvalidKeyException if the key is of the wrong type or is
     *      not 256-bits in length.  This will also be thrown if the opmode
     *      parameter is not {@code Cipher.ENCRYPT_MODE} or
     *      {@code Cipher.DECRYPT_MODE} (excepting the UOE case above).
     * @throws InvalidAlgorithmParameterException if {@code params} is
     *      not a {@code ChaCha20ParameterSpec}
     * @throws NullPointerException if {@code params} is {@code null}
     */
    @Override
    protected void engineInit(int opmode, Key key,
            AlgorithmParameterSpec params, SecureRandom random)
            throws InvalidKeyException, InvalidAlgorithmParameterException {

        // If AlgorithmParameterSpec is null, then treat this like an init
        // of the form (int, Key, SecureRandom)
        if (params == null) {
            engineInit(opmode, key, random);
            return;
        }

        // We will ignore the secure random implementation and use the nonce
        // from the AlgorithmParameterSpec instead.
        byte[] newNonce = null;
        switch (mode) {
            case MODE_NONE:
                if (!(params instanceof ChaCha20ParameterSpec)) {
                    throw new InvalidAlgorithmParameterException(
                        "ChaCha20 algorithm requires ChaCha20ParameterSpec");
                }
                ChaCha20ParameterSpec chaParams = (ChaCha20ParameterSpec)params;
                newNonce = chaParams.getNonce();
                counter = ((long)chaParams.getCounter()) & 0x00000000FFFFFFFFL;
                break;
            case MODE_AEAD:
                if (!(params instanceof IvParameterSpec)) {
                    throw new InvalidAlgorithmParameterException(
                        "ChaCha20-Poly1305 requires IvParameterSpec");
                }
                IvParameterSpec ivParams = (IvParameterSpec)params;
                newNonce = ivParams.getIV();
                if (newNonce.length != 12) {
                    throw new InvalidAlgorithmParameterException(
                        "ChaCha20-Poly1305 nonce must be 12 bytes in length");
                }
                break;
            default:
                // Should never happen
                throw new RuntimeException("ChaCha20 in unsupported mode");
        }
        init(opmode, key, newNonce);
    }

    /**
     * Initialize the engine using the {@code AlgorithmParameter} initialization
     * format.  This cipher does supports initialization with
     * {@code AlgorithmParameter} objects for ChaCha20-Poly1305 but not for
     * ChaCha20 as a simple stream cipher.  In the latter case, it will throw
     * an {@code InvalidAlgorithmParameterException} if the value is non-null.
     * If a null value is supplied for the {@code params} field
     * the cipher will be initialized with the counter value set to 1 and
     * a random nonce.  If {@code null} is used for the random object,
     * then an internal secure random source will be used to create the
     * nonce.
     *
     * @param opmode the type of operation to do.  This value must be either
     *      {@code Cipher.ENCRYPT_MODE} or {@code Cipher.DECRYPT_MODE}
     * @param key a 256-bit key suitable for ChaCha20
     * @param params a {@code null} value if the algorithm is ChaCha20, or
     *      the appropriate {@code AlgorithmParameters} object containing the
     *      nonce information if the algorithm is ChaCha20-Poly1305.
     * @param random a {@code SecureRandom} implementation, may be {@code null}.
     *
     * @throws UnsupportedOperationException if the mode of operation
     *      is {@code Cipher.WRAP_MODE} or {@code Cipher.UNWRAP_MODE}
     *      (currently unsupported).
     * @throws InvalidKeyException if the key is of the wrong type or is
     *      not 256-bits in length.  This will also be thrown if the opmode
     *      parameter is not {@code Cipher.ENCRYPT_MODE} or
     *      {@code Cipher.DECRYPT_MODE} (excepting the UOE case above).
     * @throws InvalidAlgorithmParameterException if {@code params} is
     *      non-null and the algorithm is ChaCha20.  This exception will be
     *      also thrown if the algorithm is ChaCha20-Poly1305 and an incorrect
     *      {@code AlgorithmParameters} object is supplied.
     */
    @Override
    protected void engineInit(int opmode, Key key,
            AlgorithmParameters params, SecureRandom random)
            throws InvalidKeyException, InvalidAlgorithmParameterException {

        // If AlgorithmParameters is null, then treat this like an init
        // of the form (int, Key, SecureRandom)
        if (params == null) {
            engineInit(opmode, key, random);
            return;
        }

        byte[] newNonce = null;
        switch (mode) {
            case MODE_NONE:
                throw new InvalidAlgorithmParameterException(
                        "AlgorithmParameters not supported");
            case MODE_AEAD:
                String paramAlg = params.getAlgorithm();
                if (!paramAlg.equalsIgnoreCase("ChaCha20-Poly1305")) {
                    throw new InvalidAlgorithmParameterException(
                            "Invalid parameter type: " + paramAlg);
                }
                try {
                    DerValue dv = new DerValue(params.getEncoded());
                    newNonce = dv.getOctetString();
                    if (newNonce.length != 12) {
                        throw new InvalidAlgorithmParameterException(
                                "ChaCha20-Poly1305 nonce must be " +
                                "12 bytes in length");
                    }
                } catch (IOException ioe) {
                    throw new InvalidAlgorithmParameterException(ioe);
                }
                break;
            default:
                throw new RuntimeException("Invalid mode: " + mode);
        }

        // If after all the above processing we still don't have a nonce value
        // then supply a random one provided a random source has been given.
        if (newNonce == null) {
            newNonce = createRandomNonce(random);
        }

        // Continue with initialization
        init(opmode, key, newNonce);
    }

    /**
     * Update additional authenticated data (AAD).
     *
     * @param src the byte array containing the authentication data.
     * @param offset the starting offset in the buffer to update.
     * @param len the amount of authentication data to update.
     *
     * @throws IllegalStateException if the cipher has not been initialized,
     *      {@code engineUpdate} has been called, or the cipher is running
     *      in a non-AEAD mode of operation.  It will also throw this
     *      exception if the submitted AAD would overflow a 64-bit length
     *      counter.
     */
    @Override
    protected void engineUpdateAAD(byte[] src, int offset, int len) {
        if (!initialized) {
            // We know that the cipher has not been initialized if the key
            // is still null.
            throw new IllegalStateException(
                    "Attempted to update AAD on uninitialized Cipher");
        } else if (aadDone) {
            // No AAD updates allowed after the PT/CT update method is called
            throw new IllegalStateException("Attempted to update AAD on " +
                    "Cipher after plaintext/ciphertext update");
        } else if (mode != MODE_AEAD) {
            throw new IllegalStateException(
                    "Cipher is running in non-AEAD mode");
        } else {
            try {
                aadLen = Math.addExact(aadLen, len);
                authUpdate(src, offset, len);
            } catch (ArithmeticException ae) {
                throw new IllegalStateException("AAD overflow", ae);
            }
        }
    }

    /**
     * Update additional authenticated data (AAD).
     *
     * @param src the ByteBuffer containing the authentication data.
     *
     * @throws IllegalStateException if the cipher has not been initialized,
     *      {@code engineUpdate} has been called, or the cipher is running
     *      in a non-AEAD mode of operation.  It will also throw this
     *      exception if the submitted AAD would overflow a 64-bit length
     *      counter.
     */
    @Override
    protected void engineUpdateAAD(ByteBuffer src) {
        if (!initialized) {
            // We know that the cipher has not been initialized if the key
            // is still null.
            throw new IllegalStateException(
                    "Attempted to update AAD on uninitialized Cipher");
        } else if (aadDone) {
            // No AAD updates allowed after the PT/CT update method  is called
            throw new IllegalStateException("Attempted to update AAD on " +
                    "Cipher after plaintext/ciphertext update");
        } else if (mode != MODE_AEAD) {
            throw new IllegalStateException(
                    "Cipher is running in non-AEAD mode");
        } else {
            try {
                aadLen = Math.addExact(aadLen, (src.limit() - src.position()));
                authenticator.engineUpdate(src);
            } catch (ArithmeticException ae) {
                throw new IllegalStateException("AAD overflow", ae);
            }
        }
    }

    /**
     * Create a random 12-byte nonce.
     *
     * @param random a {@code SecureRandom} object.  If {@code null} is
     * provided a new {@code SecureRandom} object will be instantiated.
     *
     * @return a 12-byte array containing the random nonce.
     */
    private static byte[] createRandomNonce(SecureRandom random) {
        byte[] newNonce = new byte[12];
        SecureRandom rand = (random != null) ? random : new SecureRandom();
        rand.nextBytes(newNonce);
        return newNonce;
    }

    /**
     * Perform additional initialization actions based on the key and operation
     * type.
     *
     * @param opmode the type of operation to do.  This value must be either
     *      {@code Cipher.ENCRYPT_MODE} or {@code Cipher.DECRYPT_MODE}
     * @param key a 256-bit key suitable for ChaCha20
     * @param newNonce the new nonce value for this initialization.
     *
     * @throws UnsupportedOperationException if the {@code opmode} parameter
     *      is {@code Cipher.WRAP_MODE} or {@code Cipher.UNWRAP_MODE}
     *      (currently unsupported).
     * @throws InvalidKeyException if the {@code opmode} parameter is not
     *      {@code Cipher.ENCRYPT_MODE} or {@code Cipher.DECRYPT_MODE}, or
     *      if the key format is not {@code RAW}.
     */
    private void init(int opmode, Key key, byte[] newNonce)
            throws InvalidKeyException {
        // Cipher.init() already checks opmode to be:
        // ENCRYPT_MODE/DECRYPT_MODE/WRAP_MODE/UNWRAP_MODE
        if ((opmode == Cipher.WRAP_MODE) || (opmode == Cipher.UNWRAP_MODE)) {
            throw new UnsupportedOperationException(
                    "WRAP_MODE and UNWRAP_MODE are not currently supported");
        }

        // Make sure that the provided key and nonce are unique before
        // assigning them to the object.
        byte[] newKeyBytes = getEncodedKey(key);
        checkKeyAndNonce(newKeyBytes, newNonce);
        if (this.keyBytes != null) {
            Arrays.fill(this.keyBytes, (byte)0);
        }
        this.keyBytes = newKeyBytes;
        nonce = newNonce;

        // Now that we have the key and nonce, we can build the initial state
        setInitialState();

        if (mode == MODE_NONE) {
            engine = new EngineStreamOnly();
        } else if (mode == MODE_AEAD) {
            if (opmode == Cipher.ENCRYPT_MODE) {
                engine = new EngineAEADEnc();
            } else if (opmode == Cipher.DECRYPT_MODE) {
                engine = new EngineAEADDec();
            } else {
                throw new InvalidKeyException("Not encrypt or decrypt mode");
            }
        }

        // We can also get one block's worth of keystream created
        finalCounterValue = counter + MAX_UINT32;
        generateKeystream();
        direction = opmode;
        aadDone = false;
        this.keyStrOffset = 0;
        initialized = true;
    }

    /**
     * Check the key and nonce bytes to make sure that they do not repeat
     * across reinitialization.
     *
     * @param newKeyBytes the byte encoding for the newly provided key
     * @param newNonce the new nonce to be used with this initialization
     *
     * @throws InvalidKeyException if both the key and nonce match the
     *      previous initialization.
     *
     */
    private void checkKeyAndNonce(byte[] newKeyBytes, byte[] newNonce)
            throws InvalidKeyException {
        // A new initialization must have either a different key or nonce
        // so the starting state for each block is not the same as the
        // previous initialization.
        if (MessageDigest.isEqual(newKeyBytes, keyBytes) &&
                MessageDigest.isEqual(newNonce, nonce)) {
            throw new InvalidKeyException(
                    "Matching key and nonce from previous initialization");
        }
    }

    /**
     * Return the encoded key as a byte array
     *
     * @param key the {@code Key} object used for this {@code Cipher}
     *
     * @return the key bytes
     *
     * @throws InvalidKeyException if the key is of the wrong type or length,
     *      or if the key encoding format is not {@code RAW}.
     */
    private static byte[] getEncodedKey(Key key) throws InvalidKeyException {
        if ("RAW".equals(key.getFormat()) == false) {
            throw new InvalidKeyException("Key encoding format must be RAW");
        }
        byte[] encodedKey = key.getEncoded();
        if (encodedKey == null || encodedKey.length != 32) {
            if (encodedKey != null) {
                Arrays.fill(encodedKey, (byte)0);
            }
            throw new InvalidKeyException("Key length must be 256 bits");
        }
        return encodedKey;
    }

    /**
     * Update the currently running operation with additional data
     *
     * @param in the plaintext or ciphertext input bytes (depending on the
     *      operation type).
     * @param inOfs the offset into the input array
     * @param inLen the length of the data to use for the update operation.
     *
     * @return the resulting plaintext or ciphertext bytes (depending on
     *      the operation type)
     */
    @Override
    protected byte[] engineUpdate(byte[] in, int inOfs, int inLen) {
        byte[] out = new byte[engine.getOutputSize(inLen, false)];
        try {
            engine.doUpdate(in, inOfs, inLen, out, 0);
        } catch (ShortBufferException | KeyException exc) {
            throw new RuntimeException(exc);
        }

        return out;
    }

    /**
     * Update the currently running operation with additional data
     *
     * @param in the plaintext or ciphertext input bytes (depending on the
     *      operation type).
     * @param inOfs the offset into the input array
     * @param inLen the length of the data to use for the update operation.
     * @param out the byte array that will hold the resulting data.  The array
     *      must be large enough to hold the resulting data.
     * @param outOfs the offset for the {@code out} buffer to begin writing
     *      the resulting data.
     *
     * @return the length in bytes of the data written into the {@code out}
     *      buffer.
     *
     * @throws ShortBufferException if the buffer {@code out} does not have
     *      enough space to hold the resulting data.
     */
    @Override
    protected int engineUpdate(byte[] in, int inOfs, int inLen,
            byte[] out, int outOfs) throws ShortBufferException {
        int bytesUpdated = 0;
        try {
            bytesUpdated = engine.doUpdate(in, inOfs, inLen, out, outOfs);
        } catch (KeyException ke) {
            throw new RuntimeException(ke);
        }
        return bytesUpdated;
    }

    /**
     * Complete the currently running operation using any final
     * data provided by the caller.
     *
     * @param in the plaintext or ciphertext input bytes (depending on the
     *      operation type).
     * @param inOfs the offset into the input array
     * @param inLen the length of the data to use for the update operation.
     *
     * @return the resulting plaintext or ciphertext bytes (depending on
     *      the operation type)
     *
     * @throws AEADBadTagException if, during decryption, the provided tag
     *      does not match the calculated tag.
     */
    @Override
    protected byte[] engineDoFinal(byte[] in, int inOfs, int inLen)
            throws AEADBadTagException {
        byte[] output = new byte[engine.getOutputSize(inLen, true)];
        try {
            engine.doFinal(in, inOfs, inLen, output, 0);
        } catch (ShortBufferException | KeyException exc) {
            throw new RuntimeException(exc);
        } finally {
            // Regardless of what happens, the cipher cannot be used for
            // further processing until it has been freshly initialized.
            initialized = false;
        }
        return output;
    }

    /**
     * Complete the currently running operation using any final
     * data provided by the caller.
     *
     * @param in the plaintext or ciphertext input bytes (depending on the
     *      operation type).
     * @param inOfs the offset into the input array
     * @param inLen the length of the data to use for the update operation.
     * @param out the byte array that will hold the resulting data.  The array
     *      must be large enough to hold the resulting data.
     * @param outOfs the offset for the {@code out} buffer to begin writing
     *      the resulting data.
     *
     * @return the length in bytes of the data written into the {@code out}
     *      buffer.
     *
     * @throws ShortBufferException if the buffer {@code out} does not have
     *      enough space to hold the resulting data.
     * @throws AEADBadTagException if, during decryption, the provided tag
     *      does not match the calculated tag.
     */
    @Override
    protected int engineDoFinal(byte[] in, int inOfs, int inLen, byte[] out,
            int outOfs) throws ShortBufferException, AEADBadTagException {

        int bytesUpdated = 0;
        try {
            bytesUpdated = engine.doFinal(in, inOfs, inLen, out, outOfs);
        } catch (KeyException ke) {
            throw new RuntimeException(ke);
        } finally {
            // Regardless of what happens, the cipher cannot be used for
            // further processing until it has been freshly initialized.
            initialized = false;
        }
        return bytesUpdated;
    }

    /**
     * Wrap a {@code Key} using this Cipher's current encryption parameters.
     *
     * @param key the key to wrap.  The data that will be encrypted will
     *      be the provided {@code Key} in its encoded form.
     *
     * @return a byte array consisting of the wrapped key.
     *
     * @throws UnsupportedOperationException this will (currently) always
     *      be thrown, as this method is not currently supported.
     */
    @Override
    protected byte[] engineWrap(Key key) throws IllegalBlockSizeException,
            InvalidKeyException {
        throw new UnsupportedOperationException(
                "Wrap operations are not supported");
    }

    /**
     * Unwrap a {@code Key} using this Cipher's current encryption parameters.
     *
     * @param wrappedKey the key to unwrap.
     * @param algorithm the algorithm associated with the wrapped key
     * @param type the type of the wrapped key. This is one of
     *      {@code SECRET_KEY}, {@code PRIVATE_KEY}, or {@code PUBLIC_KEY}.
     *
     * @return the unwrapped key as a {@code Key} object.
     *
     * @throws UnsupportedOperationException this will (currently) always
     *      be thrown, as this method is not currently supported.
     */
    @Override
    protected Key engineUnwrap(byte[] wrappedKey, String algorithm,
            int type) throws InvalidKeyException, NoSuchAlgorithmException {
        throw new UnsupportedOperationException(
                "Unwrap operations are not supported");
    }

    /**
     * Get the length of a provided key in bits.
     *
     * @param key the key to be evaluated
     *
     * @return the length of the key in bits
     *
     * @throws InvalidKeyException if the key is invalid or does not
     *      have an encoded form.
     */
    @Override
    protected int engineGetKeySize(Key key) throws InvalidKeyException {
        byte[] encodedKey = getEncodedKey(key);
        Arrays.fill(encodedKey, (byte)0);
        return encodedKey.length << 3;
    }

    /**
     * Set the initial state.  This will populate the state array and put the
     * key and nonce into their proper locations.  The counter field is not
     * set here.
     *
     * @throws IllegalArgumentException if the key or nonce are not in
     *      their proper lengths (32 bytes for the key, 12 bytes for the
     *      nonce).
     * @throws InvalidKeyException if the key does not support an encoded form.
     */
    private void setInitialState() throws InvalidKeyException {
        // Apply constants to first 4 words
        startState[0] = STATE_CONST_0;
        startState[1] = STATE_CONST_1;
        startState[2] = STATE_CONST_2;
        startState[3] = STATE_CONST_3;

        // Apply the key bytes as 8 32-bit little endian ints (4 through 11)
        for (int i = 0; i < 32; i += 4) {
            startState[(i / 4) + 4] = (keyBytes[i] & 0x000000FF) |
                ((keyBytes[i + 1] << 8) & 0x0000FF00) |
                ((keyBytes[i + 2] << 16) & 0x00FF0000) |
                ((keyBytes[i + 3] << 24) & 0xFF000000);
        }

        startState[12] = 0;

        // The final integers for the state are from the nonce
        // interpreted as 3 little endian integers
        for (int i = 0; i < 12; i += 4) {
            startState[(i / 4) + 13] = (nonce[i] & 0x000000FF) |
                ((nonce[i + 1] << 8) & 0x0000FF00) |
                ((nonce[i + 2] << 16) & 0x00FF0000) |
                ((nonce[i + 3] << 24) & 0xFF000000);
        }
    }

    /**
     * Using the current state and counter create the next set of keystream
     * bytes.  This method will generate the next 512 bits of keystream and
     * return it in the {@code keyStream} parameter.  Following the
     * block function the counter will be incremented.
     */
    private void generateKeystream() {
        chaCha20Block(startState, counter, keyStream);
        counter++;
    }

    /**
     * Perform a full 20-round ChaCha20 transform on the initial state.
     *
     * @param initState the starting state, not including the counter
     *      value.
     * @param counter the counter value to apply
     * @param result  the array that will hold the result of the ChaCha20
     *      block function.
     *
     * @note it is the caller's responsibility to ensure that the workState
     * is sized the same as the initState, no checking is performed internally.
     */
    private static void chaCha20Block(int[] initState, long counter,
                                      byte[] result) {
        // Create an initial state and clone a working copy
        int ws00 = STATE_CONST_0;
        int ws01 = STATE_CONST_1;
        int ws02 = STATE_CONST_2;
        int ws03 = STATE_CONST_3;
        int ws04 = initState[4];
        int ws05 = initState[5];
        int ws06 = initState[6];
        int ws07 = initState[7];
        int ws08 = initState[8];
        int ws09 = initState[9];
        int ws10 = initState[10];
        int ws11 = initState[11];
        int ws12 = (int)counter;
        int ws13 = initState[13];
        int ws14 = initState[14];
        int ws15 = initState[15];

        // Peform 10 iterations of the 8 quarter round set
        for (int round = 0; round < 10; round++) {
            ws00 += ws04;
            ws12 = Integer.rotateLeft(ws12 ^ ws00, 16);

            ws08 += ws12;
            ws04 = Integer.rotateLeft(ws04 ^ ws08, 12);

            ws00 += ws04;
            ws12 = Integer.rotateLeft(ws12 ^ ws00, 8);

            ws08 += ws12;
            ws04 = Integer.rotateLeft(ws04 ^ ws08, 7);

            ws01 += ws05;
            ws13 = Integer.rotateLeft(ws13 ^ ws01, 16);

            ws09 += ws13;
            ws05 = Integer.rotateLeft(ws05 ^ ws09, 12);

            ws01 += ws05;
            ws13 = Integer.rotateLeft(ws13 ^ ws01, 8);

            ws09 += ws13;
            ws05 = Integer.rotateLeft(ws05 ^ ws09, 7);

            ws02 += ws06;
            ws14 = Integer.rotateLeft(ws14 ^ ws02, 16);

            ws10 += ws14;
            ws06 = Integer.rotateLeft(ws06 ^ ws10, 12);

            ws02 += ws06;
            ws14 = Integer.rotateLeft(ws14 ^ ws02, 8);

            ws10 += ws14;
            ws06 = Integer.rotateLeft(ws06 ^ ws10, 7);

            ws03 += ws07;
            ws15 = Integer.rotateLeft(ws15 ^ ws03, 16);

            ws11 += ws15;
            ws07 = Integer.rotateLeft(ws07 ^ ws11, 12);

            ws03 += ws07;
            ws15 = Integer.rotateLeft(ws15 ^ ws03, 8);

            ws11 += ws15;
            ws07 = Integer.rotateLeft(ws07 ^ ws11, 7);

            ws00 += ws05;
            ws15 = Integer.rotateLeft(ws15 ^ ws00, 16);

            ws10 += ws15;
            ws05 = Integer.rotateLeft(ws05 ^ ws10, 12);

            ws00 += ws05;
            ws15 = Integer.rotateLeft(ws15 ^ ws00, 8);

            ws10 += ws15;
            ws05 = Integer.rotateLeft(ws05 ^ ws10, 7);

            ws01 += ws06;
            ws12 = Integer.rotateLeft(ws12 ^ ws01, 16);

            ws11 += ws12;
            ws06 = Integer.rotateLeft(ws06 ^ ws11, 12);

            ws01 += ws06;
            ws12 = Integer.rotateLeft(ws12 ^ ws01, 8);

            ws11 += ws12;
            ws06 = Integer.rotateLeft(ws06 ^ ws11, 7);

            ws02 += ws07;
            ws13 = Integer.rotateLeft(ws13 ^ ws02, 16);

            ws08 += ws13;
            ws07 = Integer.rotateLeft(ws07 ^ ws08, 12);

            ws02 += ws07;
            ws13 = Integer.rotateLeft(ws13 ^ ws02, 8);

            ws08 += ws13;
            ws07 = Integer.rotateLeft(ws07 ^ ws08, 7);

            ws03 += ws04;
            ws14 = Integer.rotateLeft(ws14 ^ ws03, 16);

            ws09 += ws14;
            ws04 = Integer.rotateLeft(ws04 ^ ws09, 12);

            ws03 += ws04;
            ws14 = Integer.rotateLeft(ws14 ^ ws03, 8);

            ws09 += ws14;
            ws04 = Integer.rotateLeft(ws04 ^ ws09, 7);
        }

        // Add the end working state back into the original state
        asIntLittleEndian.set(result, 0, ws00 + STATE_CONST_0);
        asIntLittleEndian.set(result, 4, ws01 + STATE_CONST_1);
        asIntLittleEndian.set(result, 8, ws02 + STATE_CONST_2);
        asIntLittleEndian.set(result, 12, ws03 + STATE_CONST_3);
        asIntLittleEndian.set(result, 16, ws04 + initState[4]);
        asIntLittleEndian.set(result, 20, ws05 + initState[5]);
        asIntLittleEndian.set(result, 24, ws06 + initState[6]);
        asIntLittleEndian.set(result, 28, ws07 + initState[7]);
        asIntLittleEndian.set(result, 32, ws08 + initState[8]);
        asIntLittleEndian.set(result, 36, ws09 + initState[9]);
        asIntLittleEndian.set(result, 40, ws10 + initState[10]);
        asIntLittleEndian.set(result, 44, ws11 + initState[11]);
        // Add the counter back into workState[12]
        asIntLittleEndian.set(result, 48, ws12 + (int)counter);
        asIntLittleEndian.set(result, 52, ws13 + initState[13]);
        asIntLittleEndian.set(result, 56, ws14 + initState[14]);
        asIntLittleEndian.set(result, 60, ws15 + initState[15]);
    }

    /**
     * Perform the ChaCha20 transform.
     *
     * @param in the array of bytes for the input
     * @param inOff the offset into the input array to start the transform
     * @param inLen the length of the data to perform the transform on.
     * @param out the output array.  It must be large enough to hold the
     *      resulting data
     * @param outOff the offset into the output array to place the resulting
     *      data.
     */
    private void chaCha20Transform(byte[] in, int inOff, int inLen,
            byte[] out, int outOff) throws KeyException {
        int remainingData = inLen;

        while (remainingData > 0) {
            int ksRemain = keyStream.length - keyStrOffset;
            if (ksRemain <= 0) {
                if (counter <= finalCounterValue) {
                    generateKeystream();
                    keyStrOffset = 0;
                    ksRemain = keyStream.length;
                } else {
                    throw new KeyException("Counter exhausted.  " +
                            "Reinitialize with new key and/or nonce");
                }
            }

            // XOR each byte in the keystream against the input
            int xformLen = Math.min(remainingData, ksRemain);
            xor(keyStream, keyStrOffset, in, inOff, out, outOff, xformLen);
            outOff += xformLen;
            inOff += xformLen;
            keyStrOffset += xformLen;
            remainingData -= xformLen;
        }
    }

    private static void xor(byte[] in1, int off1, byte[] in2, int off2,
            byte[] out, int outOff, int len) {
        while (len >= 8) {
            long v1 = (long) asLongView.get(in1, off1);
            long v2 = (long) asLongView.get(in2, off2);
            asLongView.set(out, outOff, v1 ^ v2);
            off1 += 8;
            off2 += 8;
            outOff += 8;
            len -= 8;
        }
        while (len > 0) {
            out[outOff] = (byte) (in1[off1] ^ in2[off2]);
            off1++;
            off2++;
            outOff++;
            len--;
        }
    }

    /**
     * Perform initialization steps for the authenticator
     *
     * @throws InvalidKeyException if the key is unusable for some reason
     *      (invalid length, etc.)
     */
    private void initAuthenticator() throws InvalidKeyException {
        authenticator = new Poly1305();

        // Derive the Poly1305 key from the starting state
        byte[] serializedKey = new byte[KEYSTREAM_SIZE];
        chaCha20Block(startState, 0, serializedKey);

        authenticator.engineInit(new SecretKeySpec(serializedKey, 0, 32,
                authAlgName), null);
        aadLen = 0;
        dataLen = 0;
    }

    /**
     * Update the authenticator state with data.  This routine can be used
     * to add data to the authenticator, whether AAD or application data.
     *
     * @param data the data to stir into the authenticator.
     * @param offset the offset into the data.
     * @param length the length of data to add to the authenticator.
     *
     * @return the number of bytes processed by this method.
     */
    private int authUpdate(byte[] data, int offset, int length) {
        Objects.checkFromIndexSize(offset, length, data.length);
        authenticator.engineUpdate(data, offset, length);
        return length;
    }

    /**
     * Finalize the data and return the tag.
     *
     * @param data an array containing any remaining data to process.
     * @param dataOff the offset into the data.
     * @param length the length of the data to process.
     * @param out the array to write the resulting tag into
     * @param outOff the offset to begin writing the data.
     *
     * @throws ShortBufferException if there is insufficient room to
     *      write the tag.
     */
    private void authFinalizeData(byte[] data, int dataOff, int length,
            byte[] out, int outOff) throws ShortBufferException {
        // Update with the final chunk of ciphertext, then pad to a
        // multiple of 16.
        if (data != null) {
            dataLen += authUpdate(data, dataOff, length);
        }
        authPad16(dataLen);

        // Also write the AAD and ciphertext data lengths as little-endian
        // 64-bit values.
        authWriteLengths(aadLen, dataLen, lenBuf);
        authenticator.engineUpdate(lenBuf, 0, lenBuf.length);
        byte[] tag = authenticator.engineDoFinal();
        Objects.checkFromIndexSize(outOff, tag.length, out.length);
        System.arraycopy(tag, 0, out, outOff, tag.length);
        aadLen = 0;
        dataLen = 0;
    }

    /**
     * Based on a given length of data, make the authenticator process
     * zero bytes that will pad the length out to a multiple of 16.
     *
     * @param dataLen the starting length to be padded.
     */
    private void authPad16(long dataLen) {
        // Pad out the AAD or data to a multiple of 16 bytes
        authenticator.engineUpdate(padBuf, 0,
                (TAG_LENGTH - ((int)dataLen & 15)) & 15);
    }

    /**
     * Write the two 64-bit little-endian length fields into an array
     * for processing by the poly1305 authenticator.
     *
     * @param aLen the length of the AAD.
     * @param dLen the length of the application data.
     * @param buf the buffer to write the two lengths into.
     *
     * @note it is the caller's responsibility to provide an array large
     *      enough to hold the two longs.
     */
    private void authWriteLengths(long aLen, long dLen, byte[] buf) {
        asLongLittleEndian.set(buf, 0, aLen);
        asLongLittleEndian.set(buf, Long.BYTES, dLen);
    }

    /**
     * Interface for the underlying processing engines for ChaCha20
     */
    interface ChaChaEngine {
        /**
         * Size an output buffer based on the input and where applicable
         * the current state of the engine in a multipart operation.
         *
         * @param inLength the input length.
         * @param isFinal true if this is invoked from a doFinal call.
         *
         * @return the recommended size for the output buffer.
         */
        int getOutputSize(int inLength, boolean isFinal);

        /**
         * Perform a multi-part update for ChaCha20.
         *
         * @param in the input data.
         * @param inOff the offset into the input.
         * @param inLen the length of the data to process.
         * @param out the output buffer.
         * @param outOff the offset at which to write the output data.
         *
         * @return the number of output bytes written.
         *
         * @throws ShortBufferException if the output buffer does not
         *      provide enough space.
         * @throws KeyException if the counter value has been exhausted.
         */
        int doUpdate(byte[] in, int inOff, int inLen, byte[] out, int outOff)
                throws ShortBufferException, KeyException;

        /**
         * Finalize a multi-part or single-part ChaCha20 operation.
         *
         * @param in the input data.
         * @param inOff the offset into the input.
         * @param inLen the length of the data to process.
         * @param out the output buffer.
         * @param outOff the offset at which to write the output data.
         *
         * @return the number of output bytes written.
         *
         * @throws ShortBufferException if the output buffer does not
         *      provide enough space.
         * @throws AEADBadTagException if in decryption mode the provided
         *      tag and calculated tag do not match.
         * @throws KeyException if the counter value has been exhausted.
         */
        int doFinal(byte[] in, int inOff, int inLen, byte[] out, int outOff)
                throws ShortBufferException, AEADBadTagException, KeyException;
    }

    private final class EngineStreamOnly implements ChaChaEngine {

        private EngineStreamOnly () { }

        @Override
        public int getOutputSize(int inLength, boolean isFinal) {
            // The isFinal parameter is not relevant in this kind of engine
            return inLength;
        }

        @Override
        public int doUpdate(byte[] in, int inOff, int inLen, byte[] out,
                int outOff) throws ShortBufferException, KeyException {
            if (initialized) {
               try {
                    if (out != null) {
                        Objects.checkFromIndexSize(outOff, inLen, out.length);
                    } else {
                        throw new ShortBufferException(
                                "Output buffer too small");
                    }
                } catch (IndexOutOfBoundsException iobe) {
                    throw new ShortBufferException("Output buffer too small");
                }
                if (in != null) {
                    Objects.checkFromIndexSize(inOff, inLen, in.length);
                    chaCha20Transform(in, inOff, inLen, out, outOff);
                }
                return inLen;
            } else {
                throw new IllegalStateException(
                        "Must use either a different key or iv.");
            }
        }

        @Override
        public int doFinal(byte[] in, int inOff, int inLen, byte[] out,
                int outOff) throws ShortBufferException, KeyException {
            return doUpdate(in, inOff, inLen, out, outOff);
        }
    }

    private final class EngineAEADEnc implements ChaChaEngine {

        @Override
        public int getOutputSize(int inLength, boolean isFinal) {
            return (isFinal ? Math.addExact(inLength, TAG_LENGTH) : inLength);
        }

        private EngineAEADEnc() throws InvalidKeyException {
            initAuthenticator();
            counter = 1;
        }

        @Override
        public int doUpdate(byte[] in, int inOff, int inLen, byte[] out,
                int outOff) throws ShortBufferException, KeyException {
            if (initialized) {
                // If this is the first update since AAD updates, signal that
                // we're done processing AAD info and pad the AAD to a multiple
                // of 16 bytes.
                if (!aadDone) {
                    authPad16(aadLen);
                    aadDone = true;
                }
                try {
                    if (out != null) {
                        Objects.checkFromIndexSize(outOff, inLen, out.length);
                    } else {
                        throw new ShortBufferException(
                                "Output buffer too small");
                    }
                } catch (IndexOutOfBoundsException iobe) {
                    throw new ShortBufferException("Output buffer too small");
                }
                if (in != null) {
                    Objects.checkFromIndexSize(inOff, inLen, in.length);
                    chaCha20Transform(in, inOff, inLen, out, outOff);
                    dataLen += authUpdate(out, outOff, inLen);
                }

                return inLen;
            } else {
                throw new IllegalStateException(
                        "Must use either a different key or iv.");
            }
        }

        @Override
        public int doFinal(byte[] in, int inOff, int inLen, byte[] out,
                int outOff) throws ShortBufferException, KeyException {
            // Make sure we have enough room for the remaining data (if any)
            // and the tag.
            if ((inLen + TAG_LENGTH) > (out.length - outOff)) {
                throw new ShortBufferException("Output buffer too small");
            }

            doUpdate(in, inOff, inLen, out, outOff);
            authFinalizeData(null, 0, 0, out, outOff + inLen);
            aadDone = false;
            return inLen + TAG_LENGTH;
        }
    }

    private final class EngineAEADDec implements ChaChaEngine {

        private final ByteArrayOutputStream cipherBuf;
        private final byte[] tag;

        @Override
        public int getOutputSize(int inLen, boolean isFinal) {
            // If we are performing a decrypt-update we should always return
            // zero length since we cannot return any data until the tag has
            // been consumed and verified.  CipherSpi.engineGetOutputSize will
            // always set isFinal to true to get the required output buffer
            // size.
            return (isFinal ?
                    Integer.max(Math.addExact((inLen - TAG_LENGTH),
                            cipherBuf.size()), 0) : 0);
        }

        private EngineAEADDec() throws InvalidKeyException {
            initAuthenticator();
            counter = 1;
            cipherBuf = new ByteArrayOutputStream(CIPHERBUF_BASE);
            tag = new byte[TAG_LENGTH];
        }

        @Override
        public int doUpdate(byte[] in, int inOff, int inLen, byte[] out,
                int outOff) {
            if (initialized) {
                // If this is the first update since AAD updates, signal that
                // we're done processing AAD info and pad the AAD to a multiple
                // of 16 bytes.
                if (!aadDone) {
                    authPad16(aadLen);
                    aadDone = true;
                }

                if (in != null) {
                    Objects.checkFromIndexSize(inOff, inLen, in.length);
                    cipherBuf.write(in, inOff, inLen);
                }
            } else {
                throw new IllegalStateException(
                        "Must use either a different key or iv.");
            }

            return 0;
        }

        @Override
        public int doFinal(byte[] in, int inOff, int inLen, byte[] out,
                int outOff) throws ShortBufferException, AEADBadTagException,
                KeyException {

            byte[] ctPlusTag;
            int ctPlusTagLen;
            if (cipherBuf.size() == 0 && inOff == 0) {
                // No previous data has been seen before doFinal, so we do
                // not need to hold any ciphertext in a buffer.  We can
                // process it directly from the "in" parameter.
                doUpdate(null, inOff, inLen, out, outOff);
                ctPlusTag = in;
                ctPlusTagLen = inLen;
            } else {
                doUpdate(in, inOff, inLen, out, outOff);
                ctPlusTag = cipherBuf.toByteArray();
                ctPlusTagLen = ctPlusTag.length;
            }
            cipherBuf.reset();

            // There must at least be a tag length's worth of ciphertext
            // data in the buffered input.
            if (ctPlusTagLen < TAG_LENGTH) {
                throw new AEADBadTagException("Input too short - need tag");
            }
            int ctLen = ctPlusTagLen - TAG_LENGTH;

            // Make sure we will have enough room for the output buffer
            try {
                Objects.checkFromIndexSize(outOff, ctLen, out.length);
            } catch (IndexOutOfBoundsException ioobe) {
                throw new ShortBufferException("Output buffer too small");
            }

            // Calculate and compare the tag.  Only do the decryption
            // if and only if the tag matches.
            authFinalizeData(ctPlusTag, 0, ctLen, tag, 0);
            long tagCompare = ((long)asLongView.get(ctPlusTag, ctLen) ^
                    (long)asLongView.get(tag, 0)) |
                    ((long)asLongView.get(ctPlusTag, ctLen + Long.BYTES) ^
                    (long)asLongView.get(tag, Long.BYTES));
            if (tagCompare != 0) {
                throw new AEADBadTagException("Tag mismatch");
            }
            chaCha20Transform(ctPlusTag, 0, ctLen, out, outOff);
            aadDone = false;

            return ctLen;
        }
    }

    public static final class ChaCha20Only extends ChaCha20Cipher {
        public ChaCha20Only() {
            mode = MODE_NONE;
        }
    }

    public static final class ChaCha20Poly1305 extends ChaCha20Cipher {
        public ChaCha20Poly1305() {
            mode = MODE_AEAD;
            authAlgName = "Poly1305";
        }
    }
}