Risks associated with digital signatures

Question

We are looking to develop a process to use digital signatures on PDF documents, send them via email to a line manager, who adds his digital signature as a "stamp of approval" who then emails them to a specific department for processing. Are there any risks associated with using digital signatures in adobe, and general best practices for their usage, or best practices to mitigate the risks associated with them.

Answer 1

If you procure and use commercially-issued credentials (not self-signed), digital signatures are much safer than any other signatures.
1. They tell you whether the signed document has been altered. The document's author may specify which alterations (like form fill or signing) are acceptable. A digital signature tells you what kind of alterations in the document occurred after signing. In Acrobat you can always get the signed version before any alterations occurred.
2. The digital signature tells you who the signer is (not only from the appearance but from the signing credential which is present in the signatures).
3. The signing credential of a digital signature can be verified on-line that it has not been revoked and is still good. Acrobat has a feature to embed revocation information in the document, so that you can get verification that the signing credential was good at the signing time even if you do not have Internet access.
4. In Acrobat the last signer can lock the signature, so that no other modifications of the document are allowed.
So, there are many advantages to using digital signatures. The only risk that you have is that a signing credential can be stolen if someone has an access to the computer or token where the credential is stored AND gets hold of the credential's password. Each credential is password protected, so you guard this password as you guard any other password. If you suspect that someone got hold of your credential and password you can always ask the credential's issuer to revoke this credential and to issue you a new one. In this case the only time span when someone may use your credential is the time lag between the time the credential was stolen and the time the issuer revoked it.