IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Personnel Remarks
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- Proof of identity (authentication of communications partners): a
communicating party (e.g. a person, organisation or IT system) must
be able to prove its identity beyond doubt to another party.
- Proof of origin (authentication of messages): A must be able prove
to B that a message originates from A and has not been altered.
4. Non-repudiation: the emphasis here in comparison with message
authentication is placed on verifiability with respect to third parties.
- Non-repudiation of origin: it should be impossible for A to deny
having sent a certain message to B after the event.
- Non-repudiation of receipt: it should be impossible for B to deny
having received a message sent by A after the event.
It is plain that there are connections between these objectives, but one
fundamental understanding of modern cryptography is as follows: the
guaranteeing of confidentiality and of authenticity are separate basic aims of a
cryptographic system: authentication restricts the circle of potential senders of
a message, while confidentiality restricts the circle of potential recipients.
The primary cryptographic method for preserving confidentiality is
encryption, and the primary methods of guaranteeing integrity, authenticity
and non-repudiation are hash functions, message authentication codes
(MACs), digital signatures and cryptographic protocols. The individual
cryptographic concepts are described briefly in the following.
I. Encryption
Encryption (encipherment) transforms a plaintext, in accordance with an item
of additional information known as the key, into an associated secret text
(ciphertext or enciphered text) that should not be decryptable for anyone who
does not know the key. The reverse transformation – reclaiming the plaintext
from the ciphertext – is known as decryption or decipherment. In all state-ofthe-art
encryption algorithms, plaintexts, ciphertexts and keys are each
represented as sequences of bits.
For them to be useable in practice, encryption algorithms must satisfy the
following minimum requirements:
- They should be resistant to deciphering, i.e. it must be impossible to
decrypt the ciphertext without knowledge of the key; in particular, the
quantity of possible keys must be "sufficiently large", because otherwise it
would simply be possible to try out all keys.
- They must be easy to use.
- Encryption and decryption must be "fast enough".
The requirement for resistance to deciphering must always be considered
relative to current technical and mathematical possibilities. An important
factor in the assessment of encryption algorithms is that it must be practically
impossible at the time of use to decrypt the ciphertext without knowledge of
the key, i.e. impossible with the technology available at the time within an
acceptable timescale.
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IT-Baseline Protection Manual: Oktober 2000