IT Baseline Protection Manual - The Information Warfare Site

Threats Catalogue Deliberate Acts Remarks
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T 4.35 Insecure cryptographic algorithms
The extent to which cryptographic processes increase security basically
depends on two parameters: secure cryptographic algorithms must be used and
the secret codes must be treated confidentially (for the compromising of
cryptographic codes see G 5.83).
Insecure cryptographic algorithms are characterised by the fact that a potential
perpetrator with justifiable resources is able to discover how the cryptographic
process works. In the case of encoding algorithms, this means that it is
possible to ascertain the original plain text from the encoded text without any
additional information. Here, you must take into account that relevant
resources for the perpetrator include available performance, aids such as
analysis tools, prior knowledge, time available, knowledge concerning
weaknesses, etc. Therefore, if you use insecure cryptographic algorithms,
perpetrators may be able to get round the cryptographic protection.
However, you need to examine each case separately in order to determine
whether a cryptographic algorithm is insecure. Nevertheless, there are several
criteria which indicate insecurities:
- If secret codes with actual lengths of less than 60 bits are used in
symmetric cryptographic techniques, then they can be cracked using a huge
number of computers to try out every possible code. With the increasing
performance of computers, it is to be expected that this limit will increase
to 80 bits in the future.
- If algorithms whose security is based on the problem of factorising large
numbers are used in asymmetric cryptographic techniques and signature
procedures, it is now thought that code lengths of less than 768 bits should
be considered insecure. This is founded on the progress in the development
of efficient factorisation algorithms which currently make it possible to
factorise numbers with approximately 500 bits using huge numbers of
computers. At the same time, it must be taken into account that optoelectronic
accelerators may be developed to perform a considerable
proportion of the calculations in these processes, which would speed things
up considerably.
- Hash functions which convert character strings of any length into a hash
value with a constant bit length can be considered insecure if the constant
length of the hash value is less than 128 bits, as it would otherwise be
possible to calculate two character strings which produce the same hash
value.
- Cryptographic algorithms developed by inexperienced developers that have
not been investigated scientifically should be considered potentially
insecure, as many years of experience are needed to develop secure
cryptographic algorithms.
- Unpublished cryptographic algorithms which run remarkably quickly in
software should also be considered potentially insecure. Experience shows
that secure algorithms are usually based on complex mathematical
functions.
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IT-Baseline Protection Manual: Oktober 2000