7 files declare their use of PrivateKey

CsrfTokenGenerator.php in core/lib/Drupal/Core/Access/CsrfTokenGenerator.php
IFrameUrlHelper.php in core/modules/media/src/IFrameUrlHelper.php
IFrameUrlHelperTest.php in core/modules/media/tests/src/Unit/IFrameUrlHelperTest.php
PermissionsHashGenerator.php in core/lib/Drupal/Core/Session/PermissionsHashGenerator.php
PermissionsHashGeneratorTest.php in core/tests/Drupal/Tests/Core/Session/PermissionsHashGeneratorTest.php
PrivateKeyTest.php in core/tests/Drupal/Tests/Core/PrivateKeyTest.php
UpdateProcessor.php in core/modules/update/src/UpdateProcessor.php

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