Patent Publication Number: US-7587408-B2

Title: Method and system for storing and retrieving data using hash-accessed multiple data stores

Description:
RELATED APPLICATIONS 
   This application is related to U.S. provisional application Ser. No. 60/366,805 filed Mar. 21, 2002 and from which it claims benefits under 35 U.S.C. §119(e). 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to database security, and more specifically, to a method and system for providing security in a database by providing partial access to database information in response to provided access information. 
   2. Background of the Invention 
   Present-day databases are protected from “data mining” (unauthorized copying of contents of the database) and unauthorized use (undesired access to the database) by a variety of means. Predominantly, entire databases are encrypted using an algorithm such as Data Encryption Standard (DES) or other private key/public key encryption algorithm so that access to the database requires knowledge of a key that permits decryption of the entire database. 
   A drawback of typical database encryption techniques is that once a user is permitted to access (decrypt) a particular database record, the user has access to the entire database. In some applications, it is desirable to restrict access to a database to a limited portion of the database. In the most restrictive sense, it is desirable to restrict access to only a single database element. For example, such security would be useful in delivery address translation systems for use by United States Postal Service (USPS) customers. Current federal statutes provide that the USPS cannot provide address lists to unrestricted and unlicensed agents, while individual address translations (from the old rural address system to the new city style address system) may be provided to anyone through a controlled process. 
   For the above reason, rural addresses that have been converted to a city-style address present an inconvenience in managing delivery operations. When using standard address matching software (known as a ZIP+4 engine) to standardize addresses, when a rural address is encountered, a cross-reference table: the Locatable Address Conversion System (LACS), must be used to convert the rural address to a city-style address. The ZIP+4 engine provides a full 11-digit ZIP code for a newer city-style address, but older rural addresses must be first converted to a newer city-style address using the LACS before an 11-digit ZIP code can be assigned. Since the LACS comprises an address list, the LACS cannot be generally distributed. 
   Typical database encryption does not provide an adequate solution for the above-described problem. Individual elements cannot typically be extracted without decrypting the database or providing a universal key and further, computation to extract small portions of the information can be quite involved as the large decryption polynomials must be computed over a significantly larger portion of the database (significantly larger than the stored element). Further, if database elements are individually protected, keys must be produced for every database element, resulting in an unworkable over-complicated system. 
   In the above-mentioned address translation application, as well as in many other protected database applications, a database protection scheme that protects all information other than information for which the corresponding access information is known (e.g., the street address of a particular customer for which the rural address is known) would be very useful. Retrieval software and a database could be supplied to anyone without enabling data mining or unauthorized access. Information could not be retrieved from the protected database without knowing the corresponding access information, but information could be retrieved knowing only the non-translated information. 
   Therefore, it would be desirable to provide a method and system for storing and retrieving information to and from a data store that provides protection of the entire database information and access to only a portion of the database information. It would further be desirable to provide a method for retrieving the information from a data store that has a relatively low computational burden. Finally it would be desirable to provide a method and system for storing and retrieving elements from a translating data store requiring only input of the non-translated information to retrieve the translation information. 
   SUMMARY OF THE INVENTION 
   The above objectives of data protection while incurring a low computational burden and requiring only entry of non-translated information to access data is accomplished in a method and system for storing and retrieving data. The method may also be embodied in a computer program product containing computer-readable program instructions for carrying out the steps of the method on a general-purpose or workstation computer system. 
   The method for storing data hashes a (generally public) piece of access information to generate a hashed result. The hashed result is then split into offset fields that are used as indices to a plurality of data stores. The input data for storage is split into data values as digits of the data according to a predetermined numeric base. The data values may be reordered before storing in the data stores by using a look-up table containing combinations of striping orders. An entry in the look-up table is selected via a field of the hashed result that selects a particular striping order. The reordered data is then stored in the corresponding data stores. 
   The method for retrieving data is similar in that the access information is again hashed to provide offsets and select the striping table entry if striping is used. The data values are retrieved via offsets of the hashed result and restored to the original order via the striping table entry. The original input data is reconstructed by computing the original stored data from the data values as digits of the input data according to the predetermined numeric base. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram depicting a computer system in which the present invention may be practiced. 
       FIG. 2  is a pictorial diagram depicting the structure of database information located in multiple data stores in accordance with an embodiment of the present invention. 
       FIG. 3  is a flowchart depicting operation of the system executing a storage method in accordance with an embodiment of the present invention. 
       FIG. 4  is a flowchart depicting operation of the system executing a retrieval method in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Referring now to the figures and in particular to  FIG. 1 , there is depicted a computer system  10  within which a method may be performed via the execution of program instructions forming a computer program product in accordance with an embodiment of the present invention. The method may employ program instructions located within a memory  19  of a workstation computer  14  and executed by a central processing unit  18  (CPU) and the data store of the present invention may be located entirely within a storage media  13 A and memory  19 . Alternatively, workstation computer  14  may be coupled via a network  11  connection for coupling workstation computer  14  to a network such as a local-area network (LAN), wide-area network (WAN) or the Internet. In a network implementation, the data store and/or program instructions for implementing the methods of the present invention may be located within a database server  12  coupled to a storage media  13 B. 
   The method of the present invention provides inherent database security, permitting distribution of a program and data store to an end-user for execution on workstation computer  14  or access to the data store and execution of the program via the Internet or other network. Other combinations such as local-hosted program with remote data store, local data store with remote-hosted program are possible and should be understood to be variations in accordance with embodiments of the present invention. 
   The present invention provides a method and system that store database information in multiple data stores, which may be individual data files, segments within a single data file, data structures within a single section of a data file or arranged in some other data storage implementation as are commonly known in the art of data storage and retrieval. The structure behind the present invention provides security without encryption, as portions of a single database element are spread across the multiple data stores. The relationship between the locations of the portions of the database element is not encoded and is therefore not extractable. The locations of the portions of the database element rather encode the access information, so that by knowing the access information, the database element can be retrieved. 
   As such, the method and system of the present invention can provide security for data where access to a database element only has a one-to-one correspondence to another piece of information (access information). In particular, two applications for the data storage and retrieval method and system of the present invention are envisioned as applied to the requirements for privacy within USPS products. The first is a rural address to new 11-digit Delivery Point Code (DPC) conversion system. Upon receiving a rural address, the database retrieval system will return the unique 11-digit DPC, along with optional hint information used for verification and resolving multiple addresses that may be coded to a singe DPC. 
   The second application is a name and address to change of address information retrieval system. Upon receiving both a name and an address, the system will return a unique 11-digit DPC and an effective move date, along with optional hint information as described above. The above-described particular applications are important for USPS operations, but should not be construed as limiting the method and system of the invention, in the sense that the technology may be applied to many database security requirements and a broad range of data storage and retrieval applications. Extra information, which may be the hint information described above may be stored in the data stores along with the 11-digit DPC (and the move date for the change of address system). Although the following description illustrates a technique for numerically encoding numeric data (e.g., the 11-digit DPC), other encoding may be used for alphanumeric data or unencoded data may be stored in one or more of the data stores. The extra information may be the middle initial and gender code for verification, and the hint information may be a code as described above for resolving multiple addresses. Other information may be stored along with the DPC and effective move date. The data storage technique should not be construed as limiting the secure addressing features used to store and access the data. 
   Referring now to  FIG. 2 , the structure of database information located in multiple data stores in accordance with an embodiment of the present invention is shown. Access information  30 , (for example, an old-style rural address or an address and name) is hashed using a Secure Hash Algorithm  31  (SHA-1). Details of SHA-1 algorithms are described in the “SECURE HASH STANDARD”, Federal Information Processing Standards Publication 180-1 issued by the National Institute of Standards and Technology (NIST), an agency of the U.S. government. The SHA-1 algorithm is typically used for producing a condensed version of a message for verification through a Digital Signature Algorithm (DSA). The condensed version of the message (the message digest) encoded in a digital signature can be compared to a message digest generated from a received for verification that the received message content is the same as the transmitted message content. The message digest is a 20-byte number that is typically used for signature/message verification, but will be used herein in a new manner to provide access to the data stores of the present invention. 
   The present invention uses the SHA-1 algorithm to produce a representation of the access information for the database element and not for the above-described original purpose of the SHA-1 algorithm. It should be understood that other algorithms may be used to produce the representation of the access information as used in the present invention and that use of the SHA-1 algorithm is a convenience and not a limitation of the present invention. 
   Access information  30  is generally pre-processed to standardize actual user input. For example, the case of alphanumeric characters may be adjusted to a single case, alphabetical representation of numbers may be converted to numeric representations, spaces may be removed, symbols and abbreviations may be standardized, etc. Given a standard access information  30 , the SHA-1 algorithm  31  yields a hashed result  32  (hashed rural address in the example). The hashed result  32  of the exemplary embodiment comprises a 20-byte number. The 20-byte hashed result  32  is then split into five 4-byte fields that are used as offsets for retrieving information from 9 separate data stores  34 . (The offsets are ANDed with a size of the corresponding data store minus one to yield an offset sized for the corresponding data store). Only data stores  1 ,  2   8  and  9  are depicted in the drawing for clarity (data stores  34 A-D). 
   Data stores  34  vary in size and their size is determined in a build process that generates data stores  34  periodically to provide updates to the software implementing the method of the present invention. The maximum size of the data stores is 2 32  bytes but generally, the table sizes will not approach this number for data sets that are smaller (such as the above-described USPS application examples, where the data store sizes typically do not exceed 2 26  bytes). Further, un-hashed input information (access information) may be used to pre-select a set of data stores. For example, the first two digits of ZIP code information in the exemplary un-hashed access information may be used to select from amongst 100 sets of data stores  34  reducing the required size of data stores by a factor of 100. The size of data stores  34  as dictated by the above-described pre-selection is a system option that may be made selectable for a particular system customer or based on the memory size of a computer system executing program instructions in accordance with embodiments of the present invention. 
   Further, data stores are set in the exemplary embodiment to sizes corresponding to powers-of-two, and specifically to the power-of-two size that will be greater than or equal to 4 times the quantity of data values to be stored. The reason for the larger storage size is that the storage method of the present invention will allow collisions between SHA-1 results and the particular storage locations within a data store (i.e., part of the hashed result will be ignored), resulting in more than a one-to-one correspondence between SHA-1 results and data value combinations. Any conflicts occurring during generation of a particular one of data stores  34  will be marked at build time, thus providing a mechanism for avoiding conflicts during data retrieval by triggering generation of a replacement offset for the data store that returns a marker value. The conflict avoidance mechanism will be described in further detail below. 
   The fields extracted from hashed result  32  in the exemplary embodiment are 32-bit numbers, therefore 5 indices are available from 20-byte hashed result  32 . The extracted fields are ANDed with the size of the associated data store minus one, yielding an offset sized to the associated data store size. When all of the fields have been used to generate offsets, hashed result  32  is itself hashed, again using the SHA-1 algorithm, and the resulting doubly-hashed element  32 A is effectively concatenated with the original hashed element  32 , yielding five more 4-byte offset fields. The above-described repeated hashing procedure can also be used and repeated as needed to avoid collisions indicated by collision flags in the data storage locations. Generating another hashed result  32  and doubly hashed result  32 A, by repeating the hashing process permits eventual generation of a set of offsets that will not collide with existing data. 
   At least two hashed results, hashed result  32  and doubly-hashed result  32 A are needed in the illustrated embodiment in order to yield at least the required 9 non-overlapping 4-byte offset fields. If overlapping fields are used (for example using a 2 byte overlap of each field) it is possible to provide 9 4-byte offsets from a single hashed result  32  in accordance with another embodiment of the invention. 
   Data values  35  stored at the offsets determined by the first 8 offsets correspond to digits of a number of a particular numeric base. However, to further secure the stored data from any possible mining or discovery and also to realize an even usage of individual data stores  34 , the data is “striped” across data stores  34  when data stores  34  are populated, so the extracted data must be un-striped in order reconstruct the original data. Striping look-up table and reordering  38  represents a process that uses the top eight bytes of hashed result  32  as an entry pointer to a look-up table. The look-up table contains all of the possible combinations of reordering of data values  35  amongst data stores  34 . Data store  8   34 D is depicted as being outside of the striping algorithm in  FIG. 2 , but may be included as well. 
   The top 8-bytes of the 20 byte SHA-1 result (hashed access information  32  shifted right by 12 bytes) is divided by 5040 and the resulting modulo 5040 result (the remainder) is used to access a striping look-up table  38 , provided as a file. However, any portion of hashed access information  32  could be used as an entry to striping look-up table  38 , since access information  32  is quasi-random. Look-up table  38  provides 5040 combinations (7! combinations, where “!” is the factorial operator and 7! is the number of possible combinations of the 7 tables). If eight tables are used, the divisor use is 40320=8! and the look-up table expanded to include 40320 combination patterns. Look-up table  38  is provided in the software that retrieves data from data stores  34 , so that extracted data can be re-ordered at the time of retrieval. The result of the look-up operation is a re-ordering of the positions of the data values extracted by hashed access information  32  in the computation of the final data output. Once the order of the original stored data pattern across data stores  34  has been determined, they are assigned in the re-ordered pattern as values for computing the retrieved element (11-digit DPC). 
   Data values  35  from data stores  34   1 - 7  are combined (once re-ordered) in an add/accumulate fashion by multiplying each data value by a numeric base raised to an power corresponding to a digit location for each re-ordered retrieved data value  35  (or by accumulating data values starting with the most significant and successively multiplying by the numeric base until a result including all digits is assembled). The numeric base chosen for the exemplary embodiment is 254, which is chosen because there are 256 values that may be stored in 1 byte and two codes  0  and  255  are reserved for special use. The digits are determined by adding 1 to the remainders, reserving code zero for representing an empty location in the data store and code  255  for marking conflicting locations. 
   For example, the 11-digit bar code 38118-4034-83 yields the following base 254 digits:
         38118403483/254=150072454 remainder 167; digit=168   150072454/254=590836 remainder 110; digit=111   590836/254=2326 remainder 32; digit=33   2326/254=9 remainder 40; digit=41   9/254=0 remainder 9; digit=10
 
which are then stored in respective data stores  34   1 - 7  as determined by the striping pattern retrieved from look-up table  38 .
       

   Data store  8  is a special data store for storing codes corresponding to “hint” information. Hint information is used for resolving ambiguities between some addresses located at the same 11-digit bar code location (such as addresses containing designators such as the ½ in some dual-unit street addresses, apartment designations in small un-coded multiple residence units, and other designations such as trailer, lobby, lot, penthouse, suite, upper/lower, etc.). Other information can be coded in data stores  34  (data stores  1 - 7 ) such as middle initial of addressee (for tie-breaker determinations when multiple addresses match or for verification of correct address) and information such as effective move-in date (for the change of address application) is inserted in and retrieved from the remaining data store locations for the change of address application. Data store  9  can be optionally incorporated to extend the amount of data or provide a location for storing information about a type of date. 
   Since the relationship between data values  35 A- 35 D is determined only by the hashed access information, a high level of security is provided by the above described database arrangement. Without knowing beforehand what each access information (e.g., rural address or address and name) is it is impossible to mine data from the database. Striping further enhances the security of data stores  34 . 
   Referring now to  FIG. 3 , a method for storing data is illustrated in accordance with an embodiment of the present invention. First, a database element is received for storage (step  41 ). The access information is pre-processed to eliminate possible duplicates (step  42 ). Next the access information is hashed using a SHA-1 algorithm to produce a hashed element (step  43 ) and the hashed access information is divided into a number of non-overlapping fields that are ANDed with the size of the corresponding data store to generate an offset for accessing each data store (step  44 ). 
   When all of the fields have been used to generate offsets, the hashed element itself is hashed using the SHA-1 algorithm and the resulting doubly-hashed element is concatenated with the original hashed element in order to yield more offset fields. The above-described procedure can be repeated as needed to avoid collisions indicated by collision flags in the data storage locations. 
   After the offsets are generated, the data values will be generated from the database element and stored. All existing data values in each of the data stores at the associated offsets are checked (step  45 ) to determine whether or not a conflict exists at that location (decision  46 ). If there is an attempt to store a second data value at a location that is already storing a data value, a replacement offset is generated for the particular data store by shifting the particular offset field right by one byte within the hashed access information. Step  45 , decision  46  and step  47  are repeated until empty locations are found for all data values (the requirement of shifting is statistically rare and the entire hashed access information should never be exhausted by the shifting process). The data storage method also relocates the data that was previously stored at the location generated from the original offset and in practice, the set of offsets that will be used to store the data can be completely generated to check for conflicts before any data storage is performed. The conflict locations are marked with code  255  so that the data retrieval method can generate replacement offsets when marker  255  is encountered. 
   Once a complete set of useable offsets is determined, the data values are computed from the database element by the above-described method of successively dividing by a numeric base (step  48 ). The remainder of each division yields a value for each successive data store. Then, the data values are reordered according to the striping look-up table entry selected by the top eight bytes of the hashed access information (step  49 ). Finally the data values are stored in locations corresponding to the final offsets (step  50 ). 
   Referring now to  FIG. 4 , a method for retrieving data is illustrated in accordance with an embodiment of the present invention. First, access information is received and pre-processed to ensure a match to the access information used to tore information in the data stores (step  61 ). Next the access information is hashed using a SHA-1 algorithm to produce a hashed element (step  62 ) and the hashed access information is divided into a number of non-overlapping fields equal to the number of data stores and ANDed with the size of the corresponding data store minus one to generate an offset for each data store (step  63 ). Then, the data values within each data store are retrieved with the corresponding offset (step  64 ). If a marker is found that indicates that a storage conflict occurred during storage (decision  65 ) the offset is shifted one byte to produce a new offset for that data store (step  66 ). Step  65  and step  66  are repeated until all of the offsets return valid data values. If any of the data values retrieved are null (indicating that data was never stored at that location), an empty result is returned (step  68 ) indicating that no stored database element corresponds to the access information provided. If all of the data values are non-null, the data values are re-ordered according to the striping table entry selected by the top 8 bytes of the hashed access information (step  70 ). Finally, the database element is assembled from the data values by multiplying by the numeric base used to generate the data store information (step  70 ) and the database element is thus returned in response to the provided access information. 
   While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form, and details may be made therein information is hashed using a SHA-1 algorithm to produce a hashed element (step  62 ) and the hashed access information is divided into a number of non-overlapping fields equal to the number of data stores and ANDed with the size of the corresponding data store minus one to generate an offset for each data store (step  63 ). Then, the data values within each data store are retrieved with the corresponding offset (step  64 ). If a marker is found that indicates that a storage conflict occurred during storage (decision  65 ) the offset is shifted one byte to produce a new offset for that data store (step  66 ). Step  65  and step  66  are repeated until all of the offsets return valid data values. If any or the data values retrieved are null (indicating that data was never stored at that location) an empty result is returned (step  68 ) indicating that no stored database element corresponds to the access information provided. If all of the data values are non-null, the data values are re-ordered according to the striping table entry selected by the top 8 bytes of the hashed access information (step  70 ). Finally, the database element is assembled from the data values by multiplying by the numeric base used to generate the data store information (step  70 ) and the database element is thus returned in response to the provided access information. 
   While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form, and details may be made therein without departing from the spirit and scope of the invention.