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Unformatted text preview: ood mode to use. Since the data is short and random, none of the shortcomings of ECB matter for this application. For normal plaintext, use CBC, CFB, or OFB. Which mode you choose depends on your specific requirements. Table 9.1 gives a summary of the security and efficiency of the various modes. CBC is generally best for encrypting files. The increase in security is significant; and while there are sometimes bit errors in stored data, there are almost never synchronization errors. If your application is software-based, CBC is almost always the best choice. ECB: CBC: Security: Security: - Plaintext patterns are not concealed. + Plaintext patterns are concealed by XORing with previous ciphertext block. - Input to the block cipher is not +Input to the block cipher is randomized; it is the same as the randomized by XORing with the plaintext. previous ciphertext block. +More than one message can be + More than one message can be encrypted with the same key. encrypted with the same key. - Plaintext is easy to manipulate, +/- Plaintext is somewhat difficult to blocks can be removed, repeated, or manipulate; blocks can be removed interchanged. from the beginning and end of the message, bits of the first block can be changed, and repetition allows some controlled changes. Efficiency: Efficiency: + Speed is the same as the block + Speed is the same as the block cipher. cipher. Ciphertext is up to one block longer - Ciphertext is up to one block longer than the plaintext, due to padding. than the plaintext, not counting the IV. - No preprocessing is possible. - No preprocessing is possible. + Processing is parallelizable. +/- Encryptions not parallelizable; decryption is parallelizable and has a random-access property. Fault-tolerance: Fault-tolerance: - A ciphertext error affects one full - A ciphertext error affects one full block of plaintext. block of plaintext and the corresponding bit in the next block. - Synchronization error is - Synchronization error is unrecoverable. u...
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- Fall '10