A signature card usually has the same format as a credit card and contains a chip. The chip usually contains three certificates, but more can be possible.
Certificates
Every certificate contains, among others, information on the owner (name, first name), the validity interval (start date and time until end date and time), the issuer (for example TeleSec of T-Systems), a fingerprint (for fast identification of a certificate's public key) and the key usage.
The three different certificates have among others an own serial number, an own fingerprint and different key usages. The three most common key usages are:
· keyEncipherment, dataEncipherment: A certificate with this key usage is used to encrypt or decrypt files.
· nonRepudiation: This certificate is used for signing files. Here the electronic signature is created.
· digitalSignature: This certificate is used in case the owner of a signature card wants to authenticate himself.