Security

* Spectrum * A. Thompson

[Funny, the REM in the program calls him A Andrews...]



Type-in the program in listing one and save it. Next, load

the program you wish to protect with 'Security' and type-in

the following commands:

MERGE "Security"

to merge 'Security' in with the program you wish to

protect. Then type:

GO TO 9900

  You should get a listing of a line containing a number to

be protected. The listing shows the text representation, or

face value, which is not necessarily its real value. You

will be shown the true value and be prompted for a new text

representation. If you press ENTER the text representation

will remain the same, or, if your input was of the same

length as the text representation, it will be replaced by

your input. If your input was not the length required, it

will ask you again until it receives one of the correct

length. When you have finished protecting your program,

delete lines 9900 onwards.

  This program changes the text representation of a number

in a listing, without changing its value, so that when the

program is listed, it appears to be correct, but if you

were to edit a line and then insert it back into the

program, it would not work. It is especially useful for

loader programs, e.g., the following program could be

changed from:

10 CLEAR 24999: LOAD ""CODE: RANDOMIZE USR 25000

to:

10 CLEAR 12345: LOAD ""CODE: RANDOMIZE USR 99999

and it would work perfectly, so long as the line was not

edited and replaced in the program.

