US Patent 9026474 Generating printable certificates to verify log authenticity

A method and system for generating printable certificates to verify log authenticity. A logging module generates a compound document that includes metadata for changes made to pages in a document. Each time a change is made to the document, such as adding stroke data, the logging module updates the compound document with the changes. The online marketplace module displays an option for purchasing a printable certificate. In response to a request for a certificate, the logging module generates a printable certificate that includes a set number of hashes for previous transactions. The verification module can recreate a transaction and generate a hash that is compared to the certificate to verify that no tampering has occurred with the document.