/*!
    \ingroup SRP

    \brief Initializes the Srp struct for usage.

    \return 0 on success.
    \return BAD_FUNC_ARG Returns when there's an issue with the arguments such
    as srp being null or SrpSide not being SRP_CLIENT_SIDE or SRP_SERVER_SIDE.
    \return NOT_COMPILED_IN Returns when a type is passed as an argument but
    hasn't been configured in the wolfCrypt build.
    \return <0 on error.

    \param srp the Srp structure to be initialized.
    \param type the hash type to be used.
    \param side the side of the communication.

    _Example_
    \code
    Srp srp;
    if (wc_SrpInit(&srp, SRP_TYPE_SHA, SRP_CLIENT_SIDE) != 0)
    {
        // Initialization error
    }
    else
    {
        wc_SrpTerm(&srp);
    }
    \endcode

    \sa wc_SrpTerm
    \sa wc_SrpSetUsername
*/
WOLFSSL_API int wc_SrpInit(Srp* srp, SrpType type, SrpSide side);

/*!
    \ingroup SRP

    \brief Releases the Srp struct resources after usage.

    \return none No returns.

    \param srp Pointer to the Srp structure to be terminated.

    _Example_
    \code
    Srp srp;
    wc_SrpInit(&srp, SRP_TYPE_SHA, SRP_CLIENT_SIDE);
    // Use srp
    wc_SrpTerm(&srp)
    \endcode

    \sa wc_SrpInit
*/
WOLFSSL_API void wc_SrpTerm(Srp* srp);

/*!
    \ingroup SRP

    \brief Sets the username. This function MUST be called after wc_SrpInit.

    \return 0 Username set successfully.
    \return BAD_FUNC_ARG: Return if srp or username is null.
    \return MEMORY_E: Returns if there is an issue allocating memory
    for srp->user
    \return < 0: Error.

    \param srp the Srp structure.
    \param username the buffer containing the username.
    \param size the username size in bytes

    _Example_
    \code
    Srp srp;
    byte username[] = "user";
    word32 usernameSize = 4;

    wc_SrpInit(&srp, SRP_TYPE_SHA, SRP_CLIENT_SIDE);
    if(wc_SrpSetUsername(&srp, username, usernameSize) != 0)
    {
        // Error occurred setting username.
    }
    wc_SrpTerm(&srp);
    \endcode

    \sa wc_SrpInit
    \sa wc_SrpSetParams
    \sa wc_SrpTerm
*/
WOLFSSL_API int wc_SrpSetUsername(Srp* srp, const byte* username, word32 size);

/*!
    \ingroup SRP

    \brief Sets the srp parameters based on the username..  Must be called
    after wc_SrpSetUsername.

    \return 0 Success
    \return BAD_FUNC_ARG Returns if srp, N, g, or salt is null or if nSz < gSz.
    \return SRP_CALL_ORDER_E Returns if wc_SrpSetParams is called before
wc_SrpSetUsername.
    \return <0 Error

    \param srp the Srp structure.
    \param N the Modulus. N = 2q+1, [q, N] are primes.
    \param nSz the N size in bytes.
    \param g the Generator modulo N.
    \param gSz the g size in bytes
    \param salt a small random salt. Specific for each username.
    \param saltSz the salt size in bytes

    _Example_
    \code
    Srp srp;
    byte username[] = "user";
    word32 usernameSize = 4;

    byte N[] = { }; // Contents of byte array N
    byte g[] = { }; // Contents of byte array g
    byte salt[] = { }; // Contents of byte array salt

    wc_SrpInit(&srp, SRP_TYPE_SHA, SRP_CLIENT_SIDE);
    wc_SrpSetUsername(&srp, username, usernameSize);

    if(wc_SrpSetParams(&srp, N, sizeof(N), g, sizeof(g), salt,
    sizeof(salt)) != 0)
    {
        // Error setting params
    }
    wc_SrpTerm(&srp);
    \endcode

    \sa wc_SrpInit
    \sa wc_SrpSetUsername
    \sa wc_SrpTerm
*/
WOLFSSL_API int wc_SrpSetParams(Srp* srp, const byte* N,    word32 nSz,
                                          const byte* g,    word32 gSz,
                                          const byte* salt, word32 saltSz);

/*!
    \ingroup SRP

    \brief Sets the password. Setting the password does not persists the
    clear password data in the srp structure. The client calculates
    x = H(salt + H(user:pswd)) and stores it in the auth field. This function
    MUST be called after wc_SrpSetParams and is CLIENT SIDE ONLY.

    \return 0 Success
    \return BAD_FUNC_ARG Returns if srp or password is null or if srp->side
    is not set to SRP_CLIENT_SIDE.
    \return SRP_CALL_ORDER_E Returns when wc_SrpSetPassword is called out
    of order.
    \return <0 Error

    \param srp The Srp structure.
    \param password The buffer containing the password.
    \param size The size of the password in bytes.

    _Example_
    \code
    Srp srp;
    byte username[] = "user";
    word32 usernameSize = 4;
    byte password[] = "password";
    word32 passwordSize = 8;

    byte N[] = { }; // Contents of byte array N
    byte g[] = { }; // Contents of byte array g
    byte salt[] = { }; // Contents of byte array salt

    wc_SrpInit(&srp, SRP_TYPE_SHA, SRP_CLIENT_SIDE);
    wc_SrpSetUsername(&srp, username, usernameSize);
    wc_SrpSetParams(&srp, N, sizeof(N), g, sizeof(g), salt, sizeof(salt));

    if(wc_SrpSetPassword(&srp, password, passwordSize) != 0)
    {
        // Error setting password
    }

    wc_SrpTerm(&srp);
    \endcode

    \sa wc_SrpInit
    \sa wc_SrpSetUsername
    \sa wc_SrpSetParams
*/
WOLFSSL_API int wc_SrpSetPassword(Srp* srp, const byte* password, word32 size);

/*!
    \ingroup SRP

    \brief Sets the verifier. This function MUST be called after
    wc_SrpSetParams and is SERVER SIDE ONLY.

    \return 0 Success
    \return BAD_FUNC_ARG Returned if srp or verifier is null or
    srp->side is not SRP_SERVER_SIDE.
    \return <0 Error

    \param srp The Srp structure.
    \param verifier The structure containing the verifier.
    \param size The verifier size in bytes.

    _Example_
    \code
    Srp srp;
    byte username[] = "user";
    word32 usernameSize = 4;

    byte N[] = { }; // Contents of byte array N
    byte g[] = { }; // Contents of byte array g
    byte salt[] = { }; // Contents of byte array salt
    wc_SrpInit(&srp, SRP_TYPE_SHA, SRP_SERVER_SIDE);
    wc_SrpSetUsername(&srp, username, usernameSize);
    wc_SrpSetParams(&srp, N, sizeof(N), g, sizeof(g), salt, sizeof(salt))
    byte verifier[] = { }; // Contents of some verifier

    if(wc_SrpSetVerifier(&srp, verifier, sizeof(verifier)) != 0)
    {
        // Error setting verifier
    }

    wc_SrpTerm(&srp);
    \endcode

    \sa wc_SrpInit
    \sa wc_SrpSetParams
    \sa wc_SrpGetVerifier
*/
WOLFSSL_API int wc_SrpSetVerifier(Srp* srp, const byte* verifier, word32 size);

/*!
    \ingroup SRP

    \brief Gets the verifier. The client calculates the verifier
    with v = g ^ x % N.
    This function MAY be called after wc_SrpSetPassword and
    is CLIENT SIDE ONLY.

    \return 0 Success
    \return BAD_FUNC_ARG Returned if srp, verifier or size is null
    or if srp->side is not SRP_CLIENT_SIDE.
    \return SRP_CALL_ORDER_E Returned if wc_SrpGetVerifier is called
    out of order.
    \return <0 Error

    \param srp The Srp structure.
    \param verifier The buffer to write the verifier.
    \param size Buffer size in bytes.  Updated with the verifier size.

    _Example_
    \code
    Srp srp;
    byte username[] = "user";
    word32 usernameSize = 4;
    byte password[] = "password";
    word32 passwordSize = 8;

    byte N[] = { }; // Contents of byte array N
    byte g[] = { }; // Contents of byte array g
    byte salt[] = { }; // Contents of byte array salt
    byte v[64];
    word32 vSz = 0;
    vSz = sizeof(v);

    wc_SrpInit(&srp, SRP_TYPE_SHA, SRP_CLIENT_SIDE);
    wc_SrpSetUsername(&srp, username, usernameSize);
    wc_SrpSetParams(&srp, N, sizeof(N), g, sizeof(g), salt, sizeof(salt))
    wc_SrpSetPassword(&srp, password, passwordSize)

    if( wc_SrpGetVerifier(&srp, v, &vSz ) != 0)
    {
        // Error getting verifier
    }
    wc_SrpTerm(&srp);
    \endcode

    \sa wc_SrpSetVerifier
    \sa wc_SrpSetPassword
*/
WOLFSSL_API int wc_SrpGetVerifier(Srp* srp, byte* verifier, word32* size);

/*!
    \ingroup SRP

    \brief Sets the private ephemeral value. The private ephemeral value
    is known as:
    a at the client side. a = random()
    b at the server side. b = random()
    This function is handy for unit test cases or if the developer wants
    to use an external
    random source to set the ephemeral value. This function MAY be called
    before wc_SrpGetPublic.

    \return 0 Success
    \return BAD_FUNC_ARG Returned if srp, private, or size is null.
    \return SRP_CALL_ORDER_E Returned if wc_SrpSetPrivate is called out
    of order.
    \return <0 Error

    \param srp the Srp structure.
    \param priv the ephemeral value.
    \param size the private size in bytes.

    _Example_
    \code
    Srp srp;
    byte username[] = "user";
    word32 usernameSize = 4;

    byte N[] = { }; // Contents of byte array N
    byte g[] = { }; // Contents of byte array g
    byte salt[] = { }; // Contents of byte array salt
    byte verifier = { }; // Contents of some verifier
    wc_SrpInit(&srp, SRP_TYPE_SHA, SRP_SERVER_SIDE);
    wc_SrpSetUsername(&srp, username, usernameSize);
    wc_SrpSetParams(&srp, N, sizeof(N), g, sizeof(g), salt, sizeof(salt))
    wc_SrpSetVerifier(&srp, verifier, sizeof(verifier))

    byte b[] = { }; // Some ephemeral value
    if( wc_SrpSetPrivate(&srp, b, sizeof(b)) != 0)
    {
        // Error setting private ephemeral
    }

    wc_SrpTerm(&srp);
    \endcode

    \sa wc_SrpGetPublic
*/
WOLFSSL_API int wc_SrpSetPrivate(Srp* srp, const byte* priv, word32 size);

/*!
    \ingroup SRP

    \brief Gets the public ephemeral value.  The public ephemeral value
    is known as:
    A at the client side. A = g ^ a % N
    B at the server side. B = (k * v + (g ˆ b % N)) % N
    This function MUST be called after wc_SrpSetPassword or wc_SrpSetVerifier.
    The function wc_SrpSetPrivate may be called before wc_SrpGetPublic.

    \return 0 Success
    \return BAD_FUNC_ARG Returned if srp, pub, or size is null.
    \return SRP_CALL_ORDER_E Returned if wc_SrpGetPublic is called out
    of order.
    \return BUFFER_E Returned if size < srp.N.
    \return <0 Error

    \param srp the Srp structure.
    \param pub the buffer to write the public ephemeral value.
    \param size the the buffer size in bytes. Will be updated with
    the ephemeral value size.

    _Example_
    \code
    Srp srp;
    byte username[] = "user";
    word32 usernameSize = 4;
    byte password[] = "password";
    word32 passwordSize = 8;

    byte N[] = { }; // Contents of byte array N
    byte g[] = { }; // Contents of byte array g
    byte salt[] = { }; // Contents of byte array salt
    wc_SrpInit(&srp, SRP_TYPE_SHA, SRP_CLIENT_SIDE);
    wc_SrpSetUsername(&srp, username, usernameSize);
    wc_SrpSetParams(&srp, N, sizeof(N), g, sizeof(g), salt, sizeof(salt));
    wc_SrpSetPassword(&srp, password, passwordSize)

    byte public[64];
    word32 publicSz = 0;

    if( wc_SrpGetPublic(&srp, public, &publicSz) != 0)
    {
        // Error getting public ephemeral
    }

    wc_SrpTerm(&srp);
    \endcode

    \sa wc_SrpSetPrivate
    \sa wc_SrpSetPassword
    \sa wc_SrpSetVerifier
*/
WOLFSSL_API int wc_SrpGetPublic(Srp* srp, byte* pub, word32* size);

/*!
    \ingroup SRP

    \brief Computes the session key.  The key can be accessed at
    srp->key after success.

    \return 0 Success
    \return BAD_FUNC_ARG Returned if srp, clientPubKey, or serverPubKey
    or if clientPubKeySz or serverPubKeySz is 0.
    \return SRP_CALL_ORDER_E Returned if wc_SrpComputeKey is called out
    of order.
    \return <0 Error

    \param srp the Srp structure.
    \param clientPubKey the client's public ephemeral value.
    \param clientPubKeySz the client's public ephemeral value size.
    \param serverPubKey the server's public ephemeral value.
    \param serverPubKeySz the server's public ephemeral value size.

    _Example_
    \code
    Srp server;

    byte username[] = "user";
        word32 usernameSize = 4;
    byte password[] = "password";
    word32 passwordSize = 8;
    byte N[] = { }; // Contents of byte array N
    byte g[] = { }; // Contents of byte array g
    byte salt[] = { }; // Contents of byte array salt
    byte verifier[] = { }; // Contents of some verifier
    byte serverPubKey[] = { }; // Contents of server pub key
    word32 serverPubKeySize = sizeof(serverPubKey);
    byte clientPubKey[64];
    word32 clientPubKeySize = 64;

    wc_SrpInit(&server, SRP_TYPE_SHA, SRP_SERVER_SIDE);
    wc_SrpSetUsername(&server, username, usernameSize);
    wc_SrpSetParams(&server, N, sizeof(N), g, sizeof(g), salt, sizeof(salt));
    wc_SrpSetVerifier(&server, verifier, sizeof(verifier));
    wc_SrpGetPublic(&server, serverPubKey, &serverPubKeySize);

    wc_SrpComputeKey(&server, clientPubKey, clientPubKeySz,
                                          serverPubKey, serverPubKeySize)
    wc_SrpTerm(&server);
    \endcode

    \sa wc_SrpGetPublic
*/
WOLFSSL_API int wc_SrpComputeKey(Srp* srp,
                                 byte* clientPubKey, word32 clientPubKeySz,
                                 byte* serverPubKey, word32 serverPubKeySz);

/*!
    \ingroup SRP

    \brief Gets the proof. This function MUST be called after wc_SrpComputeKey.

    \return 0 Success
    \return BAD_FUNC_ARG Returns if srp, proof, or size is null.
    \return BUFFER_E Returns if size is less than the hash size of srp->type.
    \return <0 Error

    \param srp the Srp structure.
    \param proof the peers proof.
    \param size the proof size in bytes.

    _Example_
    \code
    Srp cli;
    byte clientProof[SRP_MAX_DIGEST_SIZE];
    word32 clientProofSz = SRP_MAX_DIGEST_SIZE;

    // Initialize Srp following steps from previous examples

    if (wc_SrpGetProof(&cli, clientProof, &clientProofSz) != 0)
    {
        // Error getting proof
    }
    \endcode

    \sa wc_SrpComputeKey
*/
WOLFSSL_API int wc_SrpGetProof(Srp* srp, byte* proof, word32* size);

/*!
    \ingroup SRP

    \brief Verifies the peers proof. This function MUST be called before
    wc_SrpGetSessionKey.

    \return 0 Success
    \return <0 Error

    \param srp the Srp structure.
    \param proof the peers proof.
    \param size the proof size in bytes.

    _Example_
    \code
    Srp cli;
    Srp srv;
    byte clientProof[SRP_MAX_DIGEST_SIZE];
    word32 clientProofSz = SRP_MAX_DIGEST_SIZE;

    // Initialize Srp following steps from previous examples
    // First get the proof
    wc_SrpGetProof(&cli, clientProof, &clientProofSz)

    if (wc_SrpVerifyPeersProof(&srv, clientProof, clientProofSz) != 0)
    {
        // Error verifying proof
    }
    \endcode

    \sa wc_SrpGetSessionKey
    \sa wc_SrpGetProof
    \sa wc_SrpTerm
*/
WOLFSSL_API int wc_SrpVerifyPeersProof(Srp* srp, byte* proof, word32 size);