1 // Copyright 2018 Google Inc. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 // 15 //////////////////////////////////////////////////////////////////////////////// 16 17 package com.google.crypto.tink.subtle; 18 19 import com.google.crypto.tink.aead.internal.InsecureNonceXChaCha20; 20 import java.nio.ByteBuffer; 21 import java.security.GeneralSecurityException; 22 import java.security.InvalidKeyException; 23 import java.util.Arrays; 24 25 /** 26 * {@link XChaCha20} stream cipher based on 27 * https://download.libsodium.org/doc/advanced/xchacha20.html and 28 * https://tools.ietf.org/html/draft-arciszewski-xchacha-01. 29 * 30 * <p>This cipher is meant to be used to construct an AEAD with Poly1305. 31 */ 32 class XChaCha20 implements IndCpaCipher { 33 static final int NONCE_LENGTH_IN_BYTES = 24; 34 35 private final InsecureNonceXChaCha20 cipher; 36 37 /** 38 * Constructs a new XChaCha20 cipher with the supplied {@code key}. 39 * 40 * @throws IllegalArgumentException when {@code key} length is not {@link 41 * com.google.crypto.tink.aead.internal.ChaCha20Util#KEY_SIZE_IN_BYTES}. 42 */ XChaCha20(byte[] key, int initialCounter)43 XChaCha20(byte[] key, int initialCounter) throws InvalidKeyException { 44 cipher = new InsecureNonceXChaCha20(key, initialCounter); 45 } 46 47 @Override encrypt(final byte[] plaintext)48 public byte[] encrypt(final byte[] plaintext) throws GeneralSecurityException { 49 ByteBuffer output = ByteBuffer.allocate(NONCE_LENGTH_IN_BYTES + plaintext.length); 50 byte[] nonce = Random.randBytes(NONCE_LENGTH_IN_BYTES); 51 output.put(nonce); // Prepend nonce to ciphertext output. 52 cipher.encrypt(output, nonce, plaintext); 53 return output.array(); 54 } 55 56 @Override decrypt(final byte[] ciphertext)57 public byte[] decrypt(final byte[] ciphertext) throws GeneralSecurityException { 58 if (ciphertext.length < NONCE_LENGTH_IN_BYTES) { 59 throw new GeneralSecurityException("ciphertext too short"); 60 } 61 byte[] nonce = Arrays.copyOf(ciphertext, NONCE_LENGTH_IN_BYTES); 62 ByteBuffer rawCiphertext = 63 ByteBuffer.wrap( 64 ciphertext, NONCE_LENGTH_IN_BYTES, ciphertext.length - NONCE_LENGTH_IN_BYTES); 65 return cipher.decrypt(nonce, rawCiphertext); 66 } 67 } 68