| 摘要 |
The present invention permits the hash of a file to be taken on an incremental basis. It permits any part of the file to be changed while allowing a new aggregate hash to be computed based on the revised file portion and the prior total hash. The aggregate has is readily updated with each record revision without having to recompute the hash of the entire file in accordance with conventional techniques. These objectives are accomplished using two functions. The first function is an effective one-way hash function "H" for which it is computationally impossible to find two data values that hash to the same result. The second function is a commutative and associative function "F" (and inverse "Finv") and provides a mechanism for combining the aggregate hash and the hash of updated records. Examples of these latter functions include exclusive OR ("XOR") and arithmetic addition. The hash of each file record and the has of an identification of the record (i.e., a record number or key) are combined using a function ("F") whereby individual records may be extracted using the inverse of that function (Finv). In this fashion, an individual record may be extracted from the aggregate hash and updated. Each record is represented by its identification hashed together with its data content. All such record hashs are added together to provide a highly secure integrity check. This aggregate hash covers the entire database such that the tampering (or rearranging) of any data record is revealed by the use of the record identifier (i.e., record number) in the hash calculation due to its impact on the aggregate hash (e.g., the sum).
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