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Brief Full Advanced Search Search Tips (Publisher: John Wiley & Sons, Inc.) Author(s): Bruce Schneier ISBN: 0471128457 Publication Date: 01/01/96 Search this book:
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----------- Controlling Key Usage
In some applications it may be desirable to control how a session key is used. Some users may need session keys only for encryption or only for decryption. Session keys might only be authorized for use on a certain machine or at a certain time. One scheme to handle these sorts of restrictions attaches a Control Vector (CV) to the key; the control vector specifies the uses and restrictions for that key (see Section 24.1) [1025,1026]. This CV is hashed and XORed with a master key; the result is used as an encryption key to encrypt the session key. The resultant encrypted session key is then stored with the CV. To recover the session key, hash the CV and XOR it with the master key, and use the result to decrypt the encrypted session key. The advantages of this scheme are that the CV can be of arbitrary length and that it is always stored in the clear with the encrypted key. This scheme assumes quite a bit about tamperproof hardware and the inability of users to get at the keys directly. This system is discussed further in Sections 24.1 and 24.8. 8.6 Updating Keys
Imagine an encrypted data link where you want to change keys daily. Sometimes it’s a pain to distribute a new key every day. An easier solution i...
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.
- Fall '10