| 摘要 |
A first data source and a second data source are combined into a complex intermediate form or result; the first data source can be extracted from the intermediate form using the second data source. The combining mechanism can provide an alternative to the exclusive-OR combiner commonly used in stream ciphers. Each data value from the first data source is transformed by substitution using one of potentially multiple translation tables (12). The translations within each table can be changed after each substitution operation using a changes controller (18). Commonly, the just-used table is re-arranged or permuted; permutation retains invertibility, so that the ciphertext may be deciphered. As a particular design, the just-used substitution element may be exchanged with some element within the same table, as selected by the second data source, after every translation. The combiner substitution tables (12) can easily be forced to be invertible, and when they are, extraction is possible by substitution through inverse tables (24). Valid inverse tables can be maintained provided that the same second data is used by both mechanisms. This is the normal situation in stream ciphers. The combiner can also be used to combine two pseudo-random confusion streams into a more-complex confusion stream. In this case, exctraction may be unnecessary and so the combiner substitution tables need not be invertible. Thus, the translation changes need not be limited to permutations.
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