- Qt 6.5
- Qt Core
- C++ Classes
- QMessageAuthenticationCode
- Qt 6.5.2 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, const QByteArray &key = QByteArray())
| ~QMessageAuthenticationCode()
void | addData(const char *data, qsizetype length)
void | addData(const QByteArray &data)
bool | addData(QIODevice *device)
void | reset()
QByteArray | result() const
void | setKey(const QByteArray &key)

## Static Public Members

QByteArray | hash(const QByteArray &message, const QByteArray &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, const QByteArray &key = QByteArray())

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

### QMessageAuthenticationCode::~QMessageAuthenticationCode()

Destroys the object.

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

Adds the first length chars of data to the message.

### void QMessageAuthenticationCode::addData(const QByteArray &data)

This function overloads addData().

### 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(const QByteArray &message, const QByteArray &key, QCryptographicHash::Algorithm method)

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

### 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 QByteArray::toHex().

### void QMessageAuthenticationCode::setKey(const QByteArray &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);