Checksum is calculated using SHA512 and can be used to verify a downloaded attachment. A canonicalization of the XML document must be done before checksum calculation.
Canonicalization
http://www.w3.org/TR/2001/REC-xml-c14n-20010315
Type
http://www.w3.org/2001/04/xmlenc#sha512
Checksum of attachment 2020-09-02_zmluva_274-2020-OM_KZ-VOUK.pdf