IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Hardware & Software Remarks
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S 4.34 Using encryption, checksums or digital
signatures
Initiation responsibility: IT Security Management
Implementation responsibility: IT-users
If confidential information or information with high demands for integrity is
transmitted and if there is a possibility of this data being disclosed,
manipulated by unauthorised parties or changed due to technical failure, a
cryptographic procedure for the protection of the data intended for transfer
should be considered.
Protection of confidentiality by means of encryption
Confidential information should be encrypted before transmission. The
decisive features of any encryption procedure are the quality of the algorithm
and the selected key. An algorithm which has proven adequate for mediumlevel
protection is the Triple DES, which is based on the Data Encryption
Standard (DES). It is easy to implement, as example source code using the
programming language C is provided in many books. For use on stationary
and portable PCs, BSI can, under certain basic prerequisites, provide public
agencies with an offline encryption program (Chiasmus for Windows)
meeting medium-level protection requirements. An order form can be found
on the CD-ROM of this manual (see appendix: Auxiliary Materials).
In order to comply with confidentiality requirements of the information to be
transmitted, the recipient's and sender's IT system must provide sufficient
access protection for the encryption program. Where necessary, it should be
stored on an exchangeable data medium, kept under lock and key and only
used/imported when the need arises.
Integrity protection using checksums, encryption or digital signatures
If only the integrity of data intended for transfer is to be protected, it should be
clarified whether the protection should only be sufficient for incidental
alterations, i.e. due to transmission errors, or also for manipulation. If only
incidental alterations are to be detected, checksum procedures (e.g. Cyclic
Redundancy Checks) or error correction codes can be used. Protection against
manipulation is also offered by processes which create a so-called Message
Authentication Code (MAC) using a symmetric encryption algorithm (e.g.
DES) from the information to be transmitted. Other processes use an
asymmetric encryption algorithm (e.g. RSA) in combination with a hash
function and create a "digital signature". The resulting "fingerprints"
(checksum, error correction codes, MAC, digital signature) are transferred
together with the data to the recipient, who can then check them.
See S 2.46 Appropriate key management for the transmission or exchange of
any necessary keys. Further information on the use of cryptographic
procedures and products can be found in chapter 3.7 Crypto-concept.
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IT-Baseline Protection Manual: Oktober 2000