Computer file integrity verification

Apparatus for safeguarding the integrity of contents within a computer file, said apparatus comprising:

• a file associated with a first computer and containing data;
• a second computer located remote from the file, said second computer adapted to calculate a security value S, where S is based upon all the contents of the file and also depends upon a verification function f and a preselected residual value r, and to store S within a preselected location within the file;
• processing means for applying f against the entire contents of the file including S, to obtain results R;
• and
• means for comparing R against r, where r is not stored within the file;
• and
• means for determining that the file has not been modified, when R equals r.

A computer readable medium for storing a computer program that verifies the integrity of contents within a computer file by following the steps of:

• storing a security value S within the file, where S depends upon a verification function f, said file contents, and a preselected residual value r, where r is not stored within the file;
• applying f against entire contents of the file including S, to obtain results R;
• comparing R against r;
• and
• when R equals r, determining that the file has not been modified.