/usr/include/xsec/dsig/ is in libxml-security-c-dev 1.7.2-2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/xsec/dsig/DSIGAlgorithmHandlerDefault.hpp
/usr/include/xsec/dsig/DSIGConstants.hpp
/usr/include/xsec/dsig/DSIGKeyInfo.hpp
/usr/include/xsec/dsig/DSIGKeyInfoDEREncoded.hpp
/usr/include/xsec/dsig/DSIGKeyInfoExt.hpp
/usr/include/xsec/dsig/DSIGKeyInfoList.hpp
/usr/include/xsec/dsig/DSIGKeyInfoMgmtData.hpp
/usr/include/xsec/dsig/DSIGKeyInfoName.hpp
/usr/include/xsec/dsig/DSIGKeyInfoPGPData.hpp
/usr/include/xsec/dsig/DSIGKeyInfoSPKIData.hpp
/usr/include/xsec/dsig/DSIGKeyInfoValue.hpp
/usr/include/xsec/dsig/DSIGKeyInfoX509.hpp
/usr/include/xsec/dsig/DSIGObject.hpp
/usr/include/xsec/dsig/DSIGReference.hpp
/usr/include/xsec/dsig/DSIGReferenceList.hpp
/usr/include/xsec/dsig/DSIGSignature.hpp
/usr/include/xsec/dsig/DSIGSignedInfo.hpp
/usr/include/xsec/dsig/DSIGTransform.hpp
/usr/include/xsec/dsig/DSIGTransformBase64.hpp
/usr/include/xsec/dsig/DSIGTransformC14n.hpp
/usr/include/xsec/dsig/DSIGTransformEnvelope.hpp
/usr/include/xsec/dsig/DSIGTransformList.hpp
/usr/include/xsec/dsig/DSIGTransformXPath.hpp
/usr/include/xsec/dsig/DSIGTransformXPathFilter.hpp
/usr/include/xsec/dsig/DSIGTransformXSL.hpp
/usr/include/xsec/dsig/DSIGXPathFilterExpr.hpp
/usr/include/xsec/dsig/DSIGXPathHere.hpp