Method and device for protecting an application and method and device for executing a protected application thus protected

A method for protecting an application comprising code parts to be protected, the method comprising in a device comprising a processor:

• encrypting the code parts to be protected to obtain protected parts using an encryption key;
• replacing in the application the code parts to be protected by valid instructions different from the code part to be protected;
• storing information necessary for decryption of the protected parts so that the information may be used by an unprotection function configured to decrypt protected parts;
• storing the unprotection function and a protection function so that the unprotection function and the protection function can be called by calling functions;
• and
• inserting calls to the unprotection function and the protection function around each call to the code parts to be protected in the application, the protection function configured to protect the code parts.

A method for executing an application comprising at least one protected part, the method comprising in a device comprising memory and a processor executing the application:

• calling, using a function of the application, an unprotection function with an identifier of the protected part;
• retrieving information necessary for decryption of the protected part;
• decrypting the protected part using the information to obtain an unprotected part;
• overwriting in the memory, instructions in the application with the unprotected part;
• executing the unprotected part in the memory;
• and
• protecting the unprotected part in the memory.

A device for executing an application comprising at least one protected part, the device comprising:

• memory storing the application;
• and
• a processor configured to:
• execute a function of the application to call an unprotection function of the application with an identifier of the protected part;
• retrieve information necessary for decryption of the protected part;
• decrypt the protected part using the information to obtain an unprotected part of the application;
• overwrite, in the memory, instructions in the application with the unprotected part;
• execute the unprotected part of the application in the memory;
• and
• protect the unprotected part in the memory.

A non-transitory storage medium on which is stored instructions of an application that when executed by a processor causes the processor to:

• call an unprotection function with an identifier of a protected part of the application;
• retrieve information necessary for decryption of the protected part of the application;
• decrypt the protected part using the information to obtain an unprotected part of the application;
• overwrite, in the memory, instructions in the application with the unprotected part of the application;
• execute the unprotected part of the application in the memory;
• and
• protect the unprotected part of the application in the memory.