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Unformatted text preview: F such that for all a,b { , 1 } , for all public key K , if A and B are ciphertexts of a and b under public key K , respectively, then F ( A,B ) is a ciphertext of f ( a,b ) under public key K . 4 MAC based on Encryption We construct a MAC scheme based on a good block cipher E(). Suppose the block size is . For an bit message m and an bit MAC key k , the MAC is dened as the rst /n bits of E k ( m ), where n is a constant. Is the above MAC scheme secure? Why or why not? 1...
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 Spring '10
 SHENGZHONG
 Computer Security

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