/*!
    \ingroup ChaCha

    \brief This function sets the initialization vector (nonce) for a ChaCha
    object, initializing it for use as a cipher. It should be called after the
    key has been set, using wc_Chacha_SetKey. A difference nonce should be
    used for each round of encryption.

    \return 0 Returned upon successfully setting the initialization vector
    \return BAD_FUNC_ARG returned if there is an error processing the ctx
    input argument

    \param ctx pointer to the ChaCha structure on which to set the iv
    \param inIv pointer to a buffer containing the 12 byte initialization
    vector with which to initialize the ChaCha structure
    \param counter the value at which the block counter should start--usually
    zero.

    _Example_
    \code
    ChaCha enc;
    // initialize enc with wc_Chacha_SetKey
    byte iv[12];
    // initialize iv
    if( wc_Chacha_SetIV(&enc, iv, 0) != 0) {
	    // error initializing ChaCha structure
    }
    \endcode

    \sa wc_Chacha_SetKey
    \sa wc_Chacha_Process
*/
int wc_Chacha_SetIV(ChaCha* ctx, const byte* inIv, word32 counter);

/*!
    \ingroup ChaCha

    \brief This function processes the text from the buffer input, encrypts
    or decrypts it, and stores the result in the buffer output.

    \return 0 Returned upon successfully encrypting or decrypting the input
    \return BAD_FUNC_ARG returned if there is an error processing the ctx
    input argument

    \param ctx pointer to the ChaCha structure on which to set the iv
    \param output pointer to a buffer in which to store the output ciphertext
    or decrypted plaintext
    \param input pointer to the buffer containing the input plaintext to
    encrypt or the input ciphertext to decrypt
    \param msglen length of the message to encrypt or the ciphertext to decrypt

    _Example_
    \code
    ChaCha enc;
    // initialize enc with wc_Chacha_SetKey and wc_Chacha_SetIV

    byte plain[] = { // initialize plaintext };
    byte cipher[sizeof(plain)];
    if( wc_Chacha_Process(&enc, cipher, plain, sizeof(plain)) != 0) {
	    // error processing ChaCha cipher
    }
    \endcode

    \sa wc_Chacha_SetKey
    \sa wc_Chacha_Process
*/
int wc_Chacha_Process(ChaCha* ctx, byte* cipher, const byte* plain,
                              word32 msglen);

/*!
    \ingroup ChaCha

    \brief This function sets the key for a ChaCha object, initializing it for
    use as a cipher. It should be called before setting the nonce with
    wc_Chacha_SetIV, and before using it for encryption with wc_Chacha_Process.

    \return 0 Returned upon successfully setting the key
    \return BAD_FUNC_ARG returned if there is an error processing the ctx
    input argument or if the key is not 16 or 32 bytes long

    \param ctx pointer to the ChaCha structure in which to set the key
    \param key pointer to a buffer containing the 16 or 32 byte key with
    which to initialize the ChaCha structure
    \param keySz the length of the key passed in

    _Example_
    \code
    ChaCha enc;
    byte key[] = { // initialize key };

    if( wc_Chacha_SetKey(&enc, key, sizeof(key)) != 0) {
	    // error initializing ChaCha structure
    }
    \endcode

    \sa wc_Chacha_SetIV
    \sa wc_Chacha_Process
*/
int wc_Chacha_SetKey(ChaCha* ctx, const byte* key, word32 keySz);

/*!
    \ingroup ChaCha
    \brief This function sets the key and nonce for an XChaCha cipher
    context. XChaCha extends ChaCha20 to use a 192-bit nonce instead of
    96 bits, providing better security for applications that need to
    encrypt many messages with the same key.

    \return 0 On success.
    \return BAD_FUNC_ARG If ctx, key, or nonce is NULL, or if keySz is
    invalid, or if nonceSz is not XCHACHA_NONCE_BYTES (24 bytes).
    \return Other negative values on error.

    \param ctx pointer to the ChaCha structure to initialize
    \param key pointer to the key buffer (16 or 32 bytes)
    \param keySz length of the key in bytes (16 or 32)
    \param nonce pointer to the nonce buffer (must be 24 bytes)
    \param nonceSz length of the nonce in bytes (must be 24)
    \param counter initial block counter value (usually 0)

    _Example_
    \code
    ChaCha ctx;
    byte key[32] = { }; // 256-bit key
    byte nonce[24] = { }; // 192-bit nonce
    byte plaintext[100] = { }; // data to encrypt
    byte ciphertext[100];

    int ret = wc_XChacha_SetKey(&ctx, key, 32, nonce, 24, 0);
    if (ret != 0) {
        // error setting XChaCha key
    }
    wc_Chacha_Process(&ctx, ciphertext, plaintext, 100);
    \endcode

    \sa wc_Chacha_SetKey
    \sa wc_Chacha_SetIV
    \sa wc_Chacha_Process
*/
int wc_XChacha_SetKey(ChaCha *ctx, const byte *key, word32 keySz,
                      const byte *nonce, word32 nonceSz, word32 counter);