- Qt 6.11
- Qt Core
- C++ Classes
- QMessageAuthenticationCode
- Qt 6.11.1 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 = {})
`(since 6.6)` | QMessageAuthenticationCode(QMessageAuthenticationCode &&other)
| ~QMessageAuthenticationCode()
void | addData(QByteArrayView data)
bool | addData(QIODevice *device)
void | addData(const char *data, qsizetype length)
void | reset()
QByteArray | result() const
`(since 6.6)` QByteArrayView | resultView() const
void | setKey(QByteArrayView key)
`(since 6.6)` void | swap(QMessageAuthenticationCode &other)
`(since 6.6)` QMessageAuthenticationCode & | operator=(QMessageAuthenticationCode &&other)

## Static Public Members

QByteArray | hash(QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method)
`(since 6.8)` QByteArrayView | hashInto(QSpan<char> buffer, QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method)
`(since 6.8)` QByteArrayView | hashInto(QSpan<char> buffer, QSpan<const QByteArrayView> messageParts, QByteArrayView key, QCryptographicHash::Algorithm method)
`(since 6.8)` QByteArrayView | hashInto(QSpan<std::byte> buffer, QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method)
`(since 6.8)` QByteArrayView | hashInto(QSpan<std::byte> buffer, QSpan<const QByteArrayView> messageParts, QByteArrayView key, QCryptographicHash::Algorithm method)
`(since 6.8)` QByteArrayView | hashInto(QSpan<uchar> buffer, QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method)
`(since 6.8)` QByteArrayView | hashInto(QSpan<uchar> buffer, QSpan<const QByteArrayView> messageParts, QByteArrayView key, QCryptographicHash::Algorithm method)

## Detailed Description

Use the QMessageAuthenticationCode class to generate hash-based message authentication codes (HMACs). The class supports all cryptographic hash algorithms from QCryptographicHash (see also QCryptographicHash::Algorithm).

To generate a message authentication code, pass a suitable hash algorithm and secret key to the constructor. Then process the message data by calling addData() one or more times. After the full message has been processed, get the final authentication code via the 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"

For simple cases like above, you can also use the static hash() function:

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

Note: The cryptographic strength of the HMAC depends upon the size of the secret key, and the security of the underlying hash function.

See also QCryptographicHash and QCryptographicHash::Algorithm.

## 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().

### 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.

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

Adds the first length chars of data to the message.

This is an overloaded function.

### `[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.

See also hashInto().

### `[static noexcept, since 6.8]` QByteArrayView QMessageAuthenticationCode::hashInto(QSpan<char> buffer, QSpan<const QByteArrayView> messageParts, QByteArrayView key, QCryptographicHash::Algorithm method)

### `[static noexcept, since 6.8]` QByteArrayView QMessageAuthenticationCode::hashInto(QSpan<uchar> buffer, QSpan<const QByteArrayView> messageParts, QByteArrayView key, QCryptographicHash::Algorithm method)

### `[static noexcept, since 6.8]` QByteArrayView QMessageAuthenticationCode::hashInto(QSpan<std::byte> buffer, QSpan<const QByteArrayView> messageParts, QByteArrayView key, QCryptographicHash::Algorithm method)

### `[static noexcept, since 6.8]` QByteArrayView QMessageAuthenticationCode::hashInto(QSpan<char> buffer, QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method)

### `[static noexcept, since 6.8]` QByteArrayView QMessageAuthenticationCode::hashInto(QSpan<uchar> buffer, QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method)

### `[static noexcept, since 6.8]` QByteArrayView QMessageAuthenticationCode::hashInto(QSpan<std::byte> buffer, QByteArrayView message, QByteArrayView key, QCryptographicHash::Algorithm method)

Returns the authentication code for the message (message or, for the QSpan overloads, the concatenation of messageParts) using the key key and the method method.

The return value will be a sub-span of buffer, unless buffer is of insufficient size, in which case a null QByteArrayView is returned.

These functions were introduced in Qt 6.8.

See also hash().

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

Resets message data. Calling this function 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 function automatically resets the object state.

For optimal performance, call this function 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 this message authentication code with other. 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.