/usr/include/kadu/plugins/encryption_ng/ is in kadu-dev 0.12.3-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/kadu/plugins/encryption_ng/configuration/
/usr/include/kadu/plugins/encryption_ng/configuration/encryption-ng-configuration.h
/usr/include/kadu/plugins/encryption_ng/decryptor-wrapper.h
/usr/include/kadu/plugins/encryption_ng/decryptor.h
/usr/include/kadu/plugins/encryption_ng/encryption-actions.h
/usr/include/kadu/plugins/encryption_ng/encryption-chat-data.h
/usr/include/kadu/plugins/encryption_ng/encryption-manager.h
/usr/include/kadu/plugins/encryption_ng/encryption-ng-configuration-ui-handler.h
/usr/include/kadu/plugins/encryption_ng/encryption-ng-plugin.h
/usr/include/kadu/plugins/encryption_ng/encryption-provider-manager.h
/usr/include/kadu/plugins/encryption_ng/encryption-provider.h
/usr/include/kadu/plugins/encryption_ng/encryption_exports.h
/usr/include/kadu/plugins/encryption_ng/encryptor.h
/usr/include/kadu/plugins/encryption_ng/key-generator.h
/usr/include/kadu/plugins/encryption_ng/keys/
/usr/include/kadu/plugins/encryption_ng/keys/key-shared.h
/usr/include/kadu/plugins/encryption_ng/keys/key.h
/usr/include/kadu/plugins/encryption_ng/keys/keys-manager.h
/usr/include/kadu/plugins/encryption_ng/notify/
/usr/include/kadu/plugins/encryption_ng/notify/encryption-ng-notification.h