IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Organisation Remarks
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solution). In order to secure the transmission of data that is binding or subject
to proof, it can additionally be assigned a digital signature from the originator.
In this way the source and authenticity of the message can be verified by the
recipient, and any manipulation that has been carried out in the public network
can be reliably detected. To ensure the secure generation and storage of the
signature key, use is made once again of the chip card, which is an essential
component of the security concept. One extremely important point concerning
the connection of computers is the need for appropriate measures to prevent
the possibility of inadvertent incorrect switching, which is not usually detected
before or during the transmission – in contrast with telephone calls. This can
be achieved with built-in firewall functionality in the ISDN security
component. With monitoring of the signalling channel (D channel), the
security component can be set up in such a way that only explicitly
preconfigured crypto connections will be established. In connection with
PBXs, there is also provision that certain call numbers and functions can be
disabled in the exchanges. This helps to limit the extent to which the
vulnerable "remote maintenance" and "call deflection" functions can be
exploited.
In order to obtain both secure key management and fast real-time encryption
of the user data, hybrid techniques should be used. The method of symmetrical
information encryption is retained, while a key known as the session key is
exchanged with the aid of an asymmetrical procedure. In practical operation,
this proceeds entirely automatically. In this way it is possible to agree new
session keys for every new ISDN connection without any significant detriment
to operating convenience.
From the security standpoint, the end user should apply the following usage
criteria and conditions when selecting and using an ISDN security component:
(Rating: + = important to +++ = very important):
- The individual user keys and authentication information must be stored on
a secure medium (e.g. a chip card) and safeguarded with the aid of a
trustworthy signature (+++).
- For the purpose of encrypting a communication relationship (voice, data,
video, etc.), a new secret key, known as the session key, is to be agreed for
each transmission (++).
- The security services are performed automatically and are fully transparent
to the end system or end user (+).
- The security component is always set up in crypto mode for selected
connections (+++).
- The existing infrastructure should be retained in its entirety when the
security components are used (+).
- It should be possible to perform security administration for the security
components on a network-wide basis and, if possible, from a central point
(+).
- Online operational monitoring and registration of all security components
in dialogue with the management station is desirable (+).
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IT-Baseline Protection Manual: Oktober 2000