1. A system for processing digital data comprising: at least one untrusted external memory for storing data to be processed; a one time programmable memory; at least one secure processor connected to the one time programmable memory and the at least one external memory and configured to perform data processing by using the at least one untrusted external memory; at least one secure internal cache memory connected to the at least one secure processor to load or store data; and at least one secure cache translator connected to the at least one secure internal cache memory and the at least one untrusted external memory operating as a memory management unit configured by a secure cache digest table stored in the secure internal cache memory; wherein the secure cache translator is configured to: a) store into the secure cache digest table, during an initialization phase, parameters related to current processes, the parameters, being arranged on persistent and variable data pages, comprise at least a process identifier and a root digest based on node digests calculated on at least one persistent data page according to a Merkle tree structure; b) verify integrity of data pages during transfer of data pages from the secure internal cache memory to the external memory, the verification being performed by comparing a calculated root digest of persistent pages stored in the external memory with a corresponding root digest stored in the secure cache digest table and in response to a successful comparison to calculate a new root digest with node digests of variable pages combined with node digests of persistent pages and to store the obtained new root digest in the secure cache digest table and into the external memory; and c) verify integrity of data pages during transfer of data pages from the external memory to the secure internal cache memory, the verification being performed by comparison of a calculated root digest of at least one page to transfer with a corresponding digest stored in the secure cache digest table and in response to the comparison being successful, allowing the page to be used by the secure processor; wherein a versioning mechanism is used during root digest calculating, the secure processor being configured to access in a read/write mode a monotonic counter generating a version reference value in the one time programmable memory, and to load a persistent data page by verifying, in addition to the root digest, that the version reference value stored in the secure cache digest table is equal or higher than a corresponding value stored in the one time programmable memory.