Computer file integrity verification

• US 6,122,738 A
• Filed: 01/22/1998
• Issued: 09/19/2000
• Est. Priority Date: 01/22/1998
• Status: Expired due to Term

• Current Assignee: Symantec Corporation (NortonLifeLock Inc.)
• Original Assignee: Symantec Corporation (NortonLifeLock Inc.)
• Inventors: Millard, John
• Primary Examiner(s): De Cady, Albert
• Assistant Examiner(s): LAMARRE, GUY J
• Application Number:
  US09/010,939
• Time in Patent Office: 971 Days
• Field of Search: 714/758, 713/200, 713/187, 713/201, 713/176, 713/202, 713/189, 709/229, 364/200, 380/3, 380/4, 380/25, 380/49, 380/51
• US Class Current: 713/187
• CPC Class Codes: G06F 21/64 Protecting data integrity, e.g. using checksums, certificates or signatures

Abstract

System and method for verifying the integrity of contents within a computer file. A security value S is stored within the file. A verification function f is applied against the entire contents of the file including S, where f is a function of S. Results R of the applying step are compared against a preselected value r, where r is not stored within the file. When R equals r, a determination is made that the file has not been modified. f is typically a distributive invertible function such as the Cyclic Redundancy Check (CRC) function known as modulo p, where p is a prime number and is one bit greater than the length of S. Typically, the value of r is zero. Before executing the verification function f, a check generating program is first executed. This check generating program is executed by a computer that is remote from the file, further enhancing the security of the system.

Claims

1. A method for verifying the integrity of contents within a computer file, said method comprising 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 the 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.

2. The method of claim 1, wherein f is a distributive invertible function.

3. The method of claim 2, wherein f is the cyclic redundancy check function known as modulo p, p being a "polynomial".

4. The method of claim 3, wherein p is a prime number.

5. The method of claim 4, wherein the length of p is one bit greater than the length of S.

6. The method of claim 1, wherein the value of r is zero.

7. The method of claim 1, wherein a computer remote from the file executes a check generating program;

and

the check generating program calculates S and stores S within a preselected location within the file.

8. The method of claim 7 where S is calculated to be that number that will force R to be equal to r.

9. The method of claim 7, wherein, subsequent to the final step of claim 7, a user changes the contents of the file;

and

the check generating program recalculates and restores S based upon the changed contents of the file, in order to preserve the integrity of the file.

10. 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.

11. 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.