Secure element including a non-volatile memory and methods for saving and restoring data including defragmenting and compressing data stored in occupied and free regions
A secure element and method for backup of data stored in a non-volatile memory of the secure element. The method for backup of data includes de-fragmenting an area of the non-volatile memory so as to form, in the area, an occupied region and a free region. The method further includes compressing the portion of data contained in the occupied region, after de-fragmentation, and compressing the contents of the free region using a compression algorithm that is different from the one used for compressing the portion of data contained in the occupied region. In one embodiment, the occupied region is compressed using a dictionary, and the free region is compressed by applying run-length encoding (RLE). The method also includes generating a backup image containing the compressed portion of data and the compressed contents of the free region, and writing the backup image into the nonvolatile memory. The area may contain objects to be handled by a program coded in an object language. Metadata for each area may also be generated and stored in the nonvolatile memory. A method of restoring data, including configuring the secure element in a busy mode to avoid corruption of the contents, and a method for resetting the secure element, are also disclosed.
1. A method for backup of data stored in a non-volatile memory of a secure element, wherein the method comprises steps of:
de-fragmenting an area of the non-volatile memory containing at least one portion of data to be saved so as to form, in the area, an occupied region containing the at least one portion of data and a free region,
compressing the at least one portion of data contained in the occupied region using a compression algorithm by dictionary, after de-fragmentation,
compressing the contents of the free region by applying a run-length encoding of the contents,
generating a backup image containing the compressed at least one portion of data contained in the occupied region and the compressed contents of the free region, and
writing the backup image into the non-volatile memory of the secure element.
2. The method according to claim 1 , wherein the compressing is applied on localized data in several predetermined areas of the non-volatile memory, so as to produce several compressed blocks, the generation of the backup image comprising a concatenation of the compressed blocks.
3. The method according to claim 2 , wherein the area contains objects to be handled by a program coded in an object language, and wherein the objects are compressed using the dictionary.
4. The method according to claim 3 , wherein the method further comprises generating the dictionary from the objects to be compressed.
5. The method according to claim 1 , wherein the data to be saved are contained in at least one predetermined area of the non-volatile memory, and wherein the method further comprises generating and storing in the non-volatile memory metadata comprising, for each area, an address of the area.
6. The method according to claim 5 , wherein the metadata comprise integrity control information of the at least one predetermined area, or a size of the at least one predetermined area.
7. The method according to claim 6 , wherein the method further comprises generating and storing in the non-volatile memory integrity control information of the metadata.
8. The method according to claim 7 , wherein the method further comprises generating and storing in the non-volatile memory integrity control information of the generated backup image.
9. A method for resetting a secure element comprising a non-volatile memory storing data, the method comprising:
saving data using the method according to claim 1 ,
restoring the saved data.
10. A computer program product comprising a non-volatile memory having stored therein code instructions of a program for executing the steps of the method according to claim 1 , when the code instructions are executed by at least one processor.
11. A secure element comprising:
a non-volatile memory, and
at least one processor configured for saving data stored in the non-volatile memory, by performing operations including:
de-fragmenting an area of the non-volatile memory containing at least one portion of data to be saved so as to form, in the area, an occupied region containing the at least one portion of data, and a free region,
compressing the at least one portion of data contained in the occupied region using a compression algorithm by dictionary, after de-fragmentation,
compressing the contents of the free region by applying a run-length encoding of the contents,
generating a backup image containing the compressed at least one portion of data contained in the occupied region and the compressed contents of the free region, and
writing into the non-volatile memory the backup image.