Cryptography Reference
In-Depth Information
Data Integrity
The cryptographic definition of data integrity is a fairly straightforward
one: “the property whereby data has not been altered in an unauthorized
manner since the time it was created, transmitted, or stored by an autho-
rized source.”
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However, the advent of the digital computer as the primary
engine of cryptographic computation has meant that cryptographic algo-
rithms operate on data solely at the binary level. As Feistel declared with
respect to the design of the Lucifer cipher, “We shall no longer worry about
the original meaning of the messages. We shall deal only with their binary
representation.”
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It is thus important to note that in the context of digital
signatures, the specific focus of data integrity is on the
bitwise
composition
of data. This entails that integrity is defined at the finest, binary level of
electronic information coding (see figure 4.4). Given this, operations that
invalidate integrity include “insertion of bits, including entirely new data
items from fraudulent sources; deletion of bits; re-ordering of bits or groups
of bits; inversion or substitution of bits; and any combination of these.”
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In digital signature systems, the use of hash functions provides the cryp-
tographic safeguard against attempts to alter the integrity of messages after
Figure 4.4
Data integrity and the corresponding threat of forgery. Image courtesy of Dr.
Warwick Ford.
