Unformatted text preview: ility for end-to-end encryption. Table 10.3 End-to-End Encryption: Advantages and Disadvantages Advantages: Higher secrecy level. Disadvantages: Requires a more complex key-management system. Traffic analysis is possible, since routing information is not encrypted. Encryption is offline. 10.4 Encrypting Data for Storage
Encrypting data for storage and later retrieval can also be thought of in the Alice and Bob model. Alice is still sending a message to Bob, but in this case “Bob” is Alice at some future time. However, the problem is fundamentally different. In communications channels, messages in transit have no intrinsic value. If Bob doesn’t receive a particular message, Alice can always resend it. This is not true for data encrypted for storage. If Alice can’t decrypt her message, she can’t go back in time and re-encrypt it. She has lost it forever. This means that encryption applications for data storage should have some mechanisms to prevent unrecoverable errors from creeping into the ciphertext. The encryption key has the same value as the message, only it is smaller. In effect, cryptography converts large secrets into smaller ones. Being smaller, they can be easily lost. Key management procedures should assume that the same keys will be used again and again, and that data may sit on a disk for years before being decrypted. Furthermore, the keys will be around for a long time. A key used on a communications link should, ideally, exist only for the length of the communication. A key used for data storage might be needed for years, and hence must be stored securely for years. Other problems particular to encrypting computer data for storage were listed in : — The data may also exist in plaintext form, either on another disk, in another computer, or on paper. There is much more opportunity for a cryptanalyst to perform a known-plaintext attack. — In database applications, pieces of data may be smaller than the block size of most algorithms. This will cause the ciphertext to be considerably la...
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- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips