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I work for a company which decided last year to offer a PADES (PDF advanced electronique signature) for its clients. We don't do the advanced signature ourselves, we work with external AATL(Adope Approved Trust List) providers who generate the short-lived certificates and perform the signature on their side. Basically the flow is the following:

  1. We generate a PDF with placeholders for signature (if there are multiple signers then we will put several placeholders in the PDF)
  2. We send the PDF for eSealing to our external providers
  3. After eSealing, each signator digitally signs the document in his websession: a)The pdf is sent to our external provider which issues a short-lived certificate for the client b)The client confirms that he would like to sign c)The external provider signs the hash of the document with the certificate and sends the result of the signature to a TSA for timestamping d)Signature +timestamp(embedded) are put in the placeholder and the document is sent back to us e)Once all the required signers(1 or many) have signed the document, we store the document in our long term archiving system (e.g.: for 10 years)

Problem: So far so good. However, last week our external provider told us that the certificate used for timestamping is only valid for 3 years while the validity of our contracts can last for 10 years. We did a test opening one of our signed document with Acrobat Reader, changed the date of the computer (3years in the future) and we noticed some warnings on the signatures "The signature includes an embedded timestamp but it is expired"

Questions:

  1. Is it mandatory for long term non repudiation to re-timestamp each signature before expiry?
  2. Should we re-timestamp every signature or only the last signature? (Since there can be multiple signers and generally we allow a timewindow of a month so theoretically, the last signator can sign a month after the 1st signator)
  3. How things work under the hood during re-timestamping? Which data to send to the TSA for retimestamping? Where in the pdf should we put the result of the re-etimestamping?
  4. Will Adope still show the warning after re-timestamping?

thanks a lot for your help

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