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6.6 Scdaemon’s Assuan Protocol

The SC-Daemon should be started by the system to provide access to external tokens. Using Smartcards on a multi-user system does not make much sense except for system services, but in this case no regular user accounts are hosted on the machine.

A client connects to the SC-Daemon by connecting to the socket named /usr/local/var/run/gnupg/scdaemon/socket, configuration information is read from /etc/gnupg/scdaemon.conf

Each connection acts as one session, SC-Daemon takes care of synchronizing access to a token between sessions.

• Return the serial number
• Read all useful information from the card
• Return a certificate
• Return a public key
• Signing data with a Smartcard
• Decrypting data with a Smartcard
• Read an attribute’s value
• Update an attribute’s value
• Write a key to a card
• Generate a new key on-card
• Return random bytes generated on-card
• Change PINs
• Perform a VERIFY operation
• Perform a RESTART operation
• Send a verbatim APDU to the card