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18 lines
534 B
18 lines
534 B
function block = dpa_des_oracle( ciphertext, tested_sbox, key_chunk )
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%DES_ORACLE(CIPHERTEXT, TESTED_SBOX, KEY_CHUNK)
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%
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% Return the value, before the last des round, of the four bits
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% modified by the specified key_chunk during the last round
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% expand the key chunk to a 48 bit key
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key48 = dpa_des_expand_key_chunk(key_chunk, tested_sbox);
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% invert final permutation (aka initial permutation) to retrive
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% last des round result
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data = des_initial_permutation(ciphertext);
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% reapply last round
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block = des_round(data, key48);
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