- Qt 6.7
- Qt Core
- C++ Classes
- QMessageAuthenticationCode
- Qt 6.7.0 Reference Documentation

# QMessageAuthenticationCode Class

The QMessageAuthenticationCode class provides a way to generate hash-based message authentication codes. More...

Header: | #include <QMessageAuthenticationCode>
CMake: | find_package(Qt6 REQUIRED COMPONENTS Core) target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake: | QT += core

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Public Functions

| QMessageAuthenticationCode(QCryptographicHash::Algorithm method, QByteArrayView key = {})
| QMessageAuthenticationCode(QMessageAuthenticationCode &&other)
| ~QMessageAuthenticationCode()
void | addData(QByteArrayView data)
void | addData(const char *data, qsizetype length)
bool | addData(QIODevice *device)
void | reset()
QByteArray | result() const
QByteArrayView | resultView() const
void | setKey(QByteArrayView key)
void | swap(QMessageAuthenticationCode &other)
QMessageAuthenticationCode & | operator=(QMessageAuthenticationCode &&other)

## Static Public Members

QByteArray | hash(QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method)

## Detailed Description

QMessageAuthenticationCode supports all cryptographic hashes which are supported by QCryptographicHash.

To generate message authentication code, pass hash algorithm QCryptographicHash::Algorithm to constructor, then set key and message by setKey() and addData() functions. Result can be acquired by result() function.

         QByteArray key = "key";
         QByteArray message = "The quick brown fox jumps over the lazy dog";
         ...
         QMessageAuthenticationCode code(QCryptographicHash::Sha256, key);
         code.addData(message);
         code.result().toHex(); // returns "f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8"

Alternatively, this effect can be achieved by providing message, key and method to hash() method.

         QMessageAuthenticationCode::hash(message, key, QCryptographicHash::Sha256).toHex();

See also QCryptographicHash.

## Member Function Documentation

### `[explicit]` QMessageAuthenticationCode::QMessageAuthenticationCode(QCryptographicHash::Algorithm method, QByteArrayView key = {})

Constructs an object that can be used to create a cryptographic hash from data using method method and key key.

Note: In Qt versions prior to 6.6, this function took its arguments as QByteArray, not QByteArrayView. If you experience compile errors, it's because your code is passing objects that are implicitly convertible to QByteArray, but not QByteArrayView. Wrap the corresponding argument in `QByteArray{~~~}` to make the cast explicit. This is backwards-compatible with old Qt versions.

### `[noexcept, since 6.6]` QMessageAuthenticationCode::QMessageAuthenticationCode(QMessageAuthenticationCode &&other)

Move-constructs a new QMessageAuthenticationCode from other.

Note: The moved-from object other is placed in a partially-formed state, in which the only valid operations are destruction and assignment of a new object.

This function was introduced in Qt 6.6.

### `[noexcept]` QMessageAuthenticationCode::~QMessageAuthenticationCode()

Destroys the object.

### `[noexcept]` void QMessageAuthenticationCode::addData(QByteArrayView data)

Adds data to the message.

Note: In Qt versions prior to 6.6, this function took its arguments as QByteArray, not QByteArrayView. If you experience compile errors, it's because your code is passing objects that are implicitly convertible to QByteArray, but not QByteArrayView. Wrap the corresponding argument in `QByteArray{~~~}` to make the cast explicit. This is backwards-compatible with old Qt versions.

See also resultView() and result().

### void QMessageAuthenticationCode::addData(const char *data, qsizetype length)

This is an overloaded function.

Adds the first length chars of data to the message.

### bool QMessageAuthenticationCode::addData(QIODevice *device)

Reads the data from the open QIODevice device until it ends and adds it to message. Returns `true` if reading was successful.

Note: device must be already opened.

### `[static]` QByteArray QMessageAuthenticationCode::hash(QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method)

Returns the authentication code for the message message using the key key and the method method.

Note: In Qt versions prior to 6.6, this function took its arguments as QByteArray, not QByteArrayView. If you experience compile errors, it's because your code is passing objects that are implicitly convertible to QByteArray, but not QByteArrayView. Wrap the corresponding argument in `QByteArray{~~~}` to make the cast explicit. This is backwards-compatible with old Qt versions.

### `[noexcept]` void QMessageAuthenticationCode::reset()

Resets message data. Calling this method doesn't affect the key.

### QByteArray QMessageAuthenticationCode::result() const

Returns the final authentication code.

See also resultView() and QByteArray::toHex().

### `[noexcept, since 6.6]` QByteArrayView QMessageAuthenticationCode::resultView() const

Returns the final hash value.

Note that the returned view remains valid only as long as the QMessageAuthenticationCode object is not modified by other means.

This function was introduced in Qt 6.6.

See also result().

### `[noexcept]` void QMessageAuthenticationCode::setKey(QByteArrayView key)

Sets secret key. Calling this method automatically resets the object state.

For optimal performance, call this method only to change the active key, not to set an initial key, as in

     QMessageAuthenticationCode mac(method);
     mac.setKey(key); // does extra work
     use(mac);

Prefer to pass initial keys as the constructor argument:

     QMessageAuthenticationCode mac(method, key); // OK, optimal
     use(mac);

You can use std::optional to delay construction of a QMessageAuthenticationCode until you know the key:

     std::optional<QMessageAuthenticationCode> mac;
     ~~~
     key = ~~~;
     mac.emplace(method, key);
     use(*mac);

Note: In Qt versions prior to 6.6, this function took its arguments as QByteArray, not QByteArrayView. If you experience compile errors, it's because your code is passing objects that are implicitly convertible to QByteArray, but not QByteArrayView. Wrap the corresponding argument in `QByteArray{~~~}` to make the cast explicit. This is backwards-compatible with old Qt versions.

### `[noexcept, since 6.6]` void QMessageAuthenticationCode::swap(QMessageAuthenticationCode &other)

Swaps message authentication code other with this message authentication code. This operation is very fast and never fails.

This function was introduced in Qt 6.6.

### `[noexcept, since 6.6]` QMessageAuthenticationCode &QMessageAuthenticationCode::operator=(QMessageAuthenticationCode &&other)

Move-assigns other to this QMessageAuthenticationCode instance.

Note: The moved-from object other is placed in a partially-formed state, in which the only valid operations are destruction and assignment of a new object.

This function was introduced in Qt 6.6.