This tutorial provides information about the benefits and recognition of signed emails signed via the S/MIME procedure.
There is also the option to sign emails via the PGP procedure. For this method, users have to install additional plugin(s) and the public key of the respective sender has to be downloaded separately. In addition, the cryptographic key is not issued by a certification authority, but is generated privately.
Signed e-mails (S/MIME)
What is a signed e-mail
E-mail signatures are an additional protection instance to verify the sender address and the content of the message. This especially helps to unmask phishing e-mails posing as popular services (e.g., online banking, parcel services, e-mail providers, etc.). Phishing attempts are an increasingly frequent attack on user data and are sometimes more, sometimes less easily distinguishable from "real" e-mails. They are not based on malware, but on deceiving the recipient into believing that he or she has received a genuine request. More information about phishing including detailed examples can be found here: Notes on phishing emails
If you receive a signed e-mail, you can rely both on the sender address displayed and on the fact that the content of the e-mail was not manipulated during transmission.
Therefore, pay attention to the sender address! It should not say email@example.com or anything similar.
The IMT sends e-mails under firstname.lastname@example.org or email@example.com.
Who can sign own e-mails (S/MIME)
Anyone who has had their identity certified by the certification authority responsible for their e-mail address can sign e-mails. During this process, the e-mail address whose e-mails are to be signed in the future must be specified. The IMT (Center for Information and Media Technologies), for example, has the possibility to issue certificates for members of the University of Paderborn.
This includes all e-mail addresses of the following formats:
More information about application: Applying for an e-mail SSL certificate
How to recognize signed e-mails?
E-mail programs display correctly signed e-mails differently. Usually, a confirmation icon appears in the header of the message, as well as a reference to the sender.
Mobile devices (smartphones, tablets) are unfortunately an exception to the rule. The manufacturer, app used and version of the OS (Android/iOS) determine whether a notice appears or not. In our experience, most mail apps are currently unable to display the signing correctly. There are efforts by the operators to change this.
In popular desktop apps, as well as Webmail, signed emails are displayed as follows.
Display in Roundcube Appearance in Horde
Display in OWA (via Internet Explorer)
S/MIME signature and encryption
Every signed e-mail also contains the sender's public cryptographic key. Common e-mail programs store this key with the corresponding contact in the address book. If you have the ability to sign your own e-mails, you can encrypt e-mails to the contact in question from this point on.
- Signed e-mail = public key from sender
- Public key + own S/MIME certificate = option to encrypt (to the contact)