We describe how a collection of documents expressed in XML-conforming languages such as CML and XHTML can be authenticated and validated against digital signatures which make use of established X.509 certificate technology. These can be associated either with specific nodes in the XML document or with the entire document. We illustrate this with two examples. An entire journal article expressed in XML has its individual components digitally signed by separate authors, and the collection is placed in an envelope and again signed. The second example involves using a software robot agent to acquire a collection of documents from a specified URL, to perform various operations and transformations on the content, including expressing molecules in CML, and to automatically sign the various components and deposit the result in a repository. We argue that these operations can used as components for building what we term an authenticated and semantic chemical web of trust.