Brown, Bradley J. (1990, ASQC) Boeing Military Airplanes, Wichita, KS
A Sum-Of-Products checksum is a Quality Assurance tool that can provide an effective prophylaxis against deliberate software virus infection, as well as against accidental software modification. A checksum tool is a mathematical algorithm that provides for precision measurement of any software configuration ranging from a single program to an entire computer system network, with a level of discrimination that can detect the alteration of a single data bit in a multi-megabyte file. In the event that a virus or other contamination is introduced into the computer system, its presence can be detected before any damage or other additional contamination can occur.
Checksums can be used to effectively monitor subcontractor software configurations during qualification testing, establish positive configuration status accountability for software development programs, and detect unauthorized modifications to delivered software products. A checksum can also provide active control of modifications for critical computing systems such as nuclear reactor control systems, weapon system software, and programmable heart pacemaker software.
Although the basic algorithm for a checksum can be expressed easily, implementation considerations, including efficiency, integrity, and ease of use, must be reflected in the resulting checksum tool. Several approaches to checksum implementation are available which can ensure detection of software modifications even in spite of symmetry, and significant trailing null values in the data to be examined.