ENCODING DATA UTILIZING A ZERO INFORMATION GAIN FUNCTION
A method begins by dispersed storage error encoding a data segment of data in accordance with dispersed data storage parameters to produce a set of encoded data slices (EDSs). The method continues with selecting a subset of EDSs from the set of EDSs. A number of encoded data slices included the subset of EDSs is less than a decode threshold number of EDSs that is required to reproduce the data segment. The method continues with generating a subset of zero information gain (ZIG) encoded data slices, where the data segment is able to be reproduced utilizing the subset of EDSs and the subset of ZIG encoded data slices. The method continues with sending the subset of EDSs to a first memory of the DSN for storage therein and sending the subset of ZIG encoded data slices to a second memory of the DSN for storage therein.
1 . A method for execution by a computing device of a dispersed storage network (DSN), the method comprises:
dispersed storage error encoding, by the computing device, a data segment of data in accordance with dispersed data storage parameters to produce a set of encoded data slices, wherein the dispersed data storage parameters include a decode threshold number, and wherein the decode threshold number of encoded data slices of the set of encoded data slices is required to recover the data segment;
selecting, by the computing device, a subset of encoded data slices from the set of encoded data slices, wherein a number of encoded data slices included the subset of encoded data slices is less than the decode threshold number;
generating, by the computing device, a subset of zero information gain (ZIG) encoded data slices, wherein a first ZIG encoded data slice of the subset of ZIG encoded data slices is generated by matrix multiplying a first decoding matrix and a first encoded data slice of the set of encoded data slices, wherein the first encoded data slice is not included in the subset of encoded data slices, and wherein the data segment is able to be reproduced utilizing the subset of encoded data slices and the subset of ZIG encoded data slices;
sending, by the computing device, the subset of encoded data slices to a first memory of the DSN for storage therein; and
sending, by the computing device, the subset of ZIG encoded data slices to a second memory of the DSN for storage therein.
2 . The method of claim 1 , wherein generating the first ZIG encoded data slice further comprises:
matrix multiplying the first decoding matrix and the first encoded data slice to produce a vector; and
matrix multiplying the vector by a row of an encoding matrix corresponding to the first encoded data slice to produce the first ZIG encoded data slice.
3 . The method of claim 1 further comprises:
generating the first decoding matrix by:
reducing an encoding matrix to produce a square matrix that exclusively includes rows associated with the subset of encoded data slices and an encoded data slice being represented by the first ZIG encoded data slice; and
inverting the square matrix to produce the decoding matrix.
4 . The method of claim 1 , wherein the sending the subset of ZIG encoded data slices comprises:
prior to sending, obfuscating the first ZIG encoded data slice using an obfuscating function.
5 . The method of claim 4 , wherein the obfuscating function comprises one of:
exclusive ORing the first ZIG encoded data slice with an obfuscating value;
masking the first ZIG encoded data slice;
encrypting the first ZIG encoded data slice; and
performing a deterministic function on the first ZIG encoded data slice.
6 . The method of claim 1 , wherein generating the first ZIG encoded data slice further comprises:
generating a first partial encoded data slice based on the first decoding matrix, the first encoded data slice and a row of the encoding matrix corresponding to the first encoded data slice;
generating a second partial encoded data slice based on a second decoding matrix, a second encoded data slice and a row of the encoding matrix corresponding to the second encoded data slice, wherein the second encoded data slice is an encoded data slice of the set of encoded data slices and is not included in the subset of encoded data slices; and
combining the first and second partial encoded data slices to produce the first ZIG encoded data slice.
7 . A computing device of a dispersed storage network (DSN) comprises:
memory;
an interface; and
a processing module operably coupled to the memory and the interface, wherein the processing module is operable to:
dispersed storage error encode a data segment of data in accordance with dispersed data storage parameters to produce a set of encoded data slices, wherein the dispersed data storage parameters include a decode threshold number, and wherein the decode threshold number of encoded data slices of the set of encoded data slices is required to recover the data segment;
select a subset of encoded data slices from the set of encoded data slices, wherein a number of encoded data slices included the subset of encoded data slices is less than the decode threshold number;
generate a subset of zero information gain (ZIG) encoded data slices, wherein a first ZIG encoded data slice of the subset of ZIG encoded data slices is generated by matrix multiplying a first decoding matrix and a first encoded data slice of the set of encoded data slices, wherein the first encoded data slice is not included in the subset of encoded data slices, and wherein the data segment is able to be reproduced utilizing the subset of encoded data slices and the subset of ZIG encoded data slices;
send, via the interface, the subset of encoded data slices to a first memory of the DSN for storage therein; and
send, via the interface, the subset of ZIG encoded data slices to a second memory of the DSN for storage therein.
8 . The computing device of claim 7 , wherein the processing module is further operable to generate the first ZIG encoded data slice by:
matrix multiplying the first decoding matrix and the first encoded data slice to produce a vector; and
matrix multiplying the vector by a row of an encoding matrix corresponding to the first encoded data slice to produce the first ZIG encoded data slice.
9 . The computing device of claim 7 , wherein the processing module is further operable to generate the first decoding matrix by:
reducing an encoding matrix to produce a square matrix that exclusively includes rows associated with the subset of encoded data slices and an encoded data slice being represented by the first ZIG encoded data slice; and
inverting the square matrix to produce the decoding matrix.
10 . The computing device of claim 7 , wherein prior to the sending, via the interface, the subset of ZIG encoded data slices, the processing module is further operable to:
obfuscate the first ZIG encoded data slice using an obfuscating function.
11 . The computing device of claim 10 , wherein the processing module is operable to perform the obfuscating function by one of:
exclusive ORing the first ZIG encoded data slice with an obfuscating value;
masking the first ZIG encoded data slice;
encrypting the first ZIG encoded data slice; and
performing a deterministic function on the first ZIG encoded data slice.
12 . The computing device of claim 7 , wherein the processing module is further operable to generate the first ZIG encoded data slice by:
generating a first partial encoded data slice based on the first decoding matrix, the first encoded data slice and a row of the encoding matrix corresponding to the first encoded data slice;
generating a second partial encoded data slice based on a second decoding matrix, a second encoded data slice and a row of the encoding matrix corresponding to the second encoded data slice, wherein the second encoded data slice is an encoded data slice of the set of encoded data slices and is not included in the subset of encoded data slices; and
combining the first and second partial encoded data slices to produce the first ZIG encoded data slice.