In addition to ordinary signatures, CreaSign also supports serial (counter) signatures. A serial signature is a signature which signs another signature. With a serial signature you can prove the order of the signature creation. For example, you can prove that person B signed the document after it was already signed by person A.
Here is a sample scenario which illustrates how serial signatures can be used:
- A bank creates an offer and signs it to confirm its authenticy. It then sends the offer to its client.
- The client company's business rules require that the offer of the bank should be signed by at least three of its employees. Each of them signs the bank's signature and therefore creates a new serial signature. The order of the signatures in the company is not important. After all the signatures are collected, the document is sent back to the bank.
- The bank signs all the signatures from the previous step to confirm that it has received the document and will carry out its obligations.
The following figure displays a greater signature hierarchy. The
signatures and the "signed after" relation form an acyclic directed
graph.
The following types of signatures can be seen in the picture:
- A root signature is a signature which signs the whole document. A document can contain more than one root signature. The order of root signatures can not be determined. This is also the case when signatures are timestamped. The timestamp only proves that a signature was created before a specific time. The following signatures are root signatures: S1, S5 and S8.
- A serial signature is a signature that signs another signature. It can be used to prove the order of the signature creation. The following signatures are serial signatures: S2, S3, S4, S6, S7 and S9. As the figure shows, S1 was created before S3 and S4 was created before S9. However, it is not possible to determine the order of S2, S3 and S4 or the order of S6 and S9.
*Requirements: Requires CreaSign Pro (not supported by CreaSign Lite).
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