5.1 Security Requirements and Cryptographic Techniques 165
5.1.3 Integrity
Often it is necessary to be sure that a particular piece of information has not
been modified at some point in time. In the real world this may be realized
by numbering all pages of a contract and binding them together so that no
piece of paper can be exchanged, added, or removed. Or, a notary might sign
a contract and then impress it with a seal. Manual modifications are either
not allowed or must be signed by all par ties. All these techniques ensure that
no modifications can be made to the contract after it has been signed.
The digital equivalent of these techniques are digital signatures. Using
digital signatures makes it possible to verify that a message was originated