コード例 #1
0
        /// <summary>
        /// Decrypts a cipher with an authentication tag and additional data.
        /// </summary>
        /// <param name="cipher">The cipher to be decrypted.</param>
        /// <param name="nonce">The 8 byte nonce.</param>
        /// <param name="key">The 32 byte key.</param>
        /// <param name="additionalData">The additional data; may be null, otherwise between 0 and 16 bytes.</param>
        /// <returns>The decrypted cipher.</returns>
        /// <exception cref="KeyOutOfRangeException"></exception>
        /// <exception cref="NonceOutOfRangeException"></exception>
        /// <exception cref="AdditionalDataOutOfRangeException"></exception>
        /// <exception cref="CryptographicException"></exception>
        public static byte[] Decrypt(byte[] cipher, byte[] nonce, byte[] key, byte[] additionalData = null)
        {
            //additionalData can be null
            if (additionalData == null)
            {
                additionalData = new byte[0x00];
            }

            //validate the length of the key
            if (key == null || key.Length != KEYBYTES)
            {
                throw new KeyOutOfRangeException("key", (key == null) ? 0 : key.Length,
                                                 string.Format("key must be {0} bytes in length.", KEYBYTES));
            }

            //validate the length of the nonce
            if (nonce == null || nonce.Length != NPUBBYTES)
            {
                throw new NonceOutOfRangeException("nonce", (nonce == null) ? 0 : nonce.Length,
                                                   string.Format("nonce must be {0} bytes in length.", NPUBBYTES));
            }

            //validate the length of the additionalData
            if (additionalData.Length > ABYTES || additionalData.Length < 0)
            {
                throw new AdditionalDataOutOfRangeException(
                          string.Format("additionalData must be between {0} and {1} bytes in length.", 0, ABYTES));
            }

            var  message = new byte[cipher.Length - ABYTES];
            var  bin     = Marshal.AllocHGlobal(message.Length);
            long messageLength;

            var ret = SodiumLibrary.crypto_aead_chacha20poly1305_ietf_decrypt(bin, out messageLength, null, cipher, cipher.Length,
                                                                              additionalData, additionalData.Length, nonce, key);

            Marshal.Copy(bin, message, 0, (int)messageLength);
            Marshal.FreeHGlobal(bin);

            if (ret != 0)
            {
                throw new CryptographicException("Error decrypting message.");
            }

            if (message.Length == messageLength)
            {
                return(message);
            }

            //remove the trailing nulls from the array
            var tmp = new byte[messageLength];

            Array.Copy(message, 0, tmp, 0, (int)messageLength);

            return(tmp);
        }