In order to gain the access mentioned above, a signature must meet certain conditions. Most programs, including Outlook, check these conditions automatically when an e-mail with a digital signature is being sent or received, and notify the user in cases when some requirements aren’t fulfilled and so the integrity of the signature can’t be guaranteed.Since a digital signature is always associated with a certificate, it’s sensible to ensure that the certificate is current and valid. The certificate must also be issued by a trusted certifying body (certificate authority). While some e-mail programs offer their own solutions, there are a number of reliable, expert CAs that can help. Some of the best-known examples include:
Because a digital signature always works in conjunction with a certificate, it must be valid and current. The certificate also needs to have been issued by a trustworthy authority. In the US, individual states issue lists of approved cryptography certificate authorities. IdenTrust, for example, is a large provider of digital certificates for financial and healthcare businesses.
The authorities are monitored according to the US E-Sign code and the UETA to ensure that signatures are valid and take legal effect, i.e. they are enforceable.
There are also several industry organizations which address certification issues and promote relevant standards, including the Certificate Authority Security Council, the Common Computing Security Standards Forum and the CA/Browser Forum.