X2SECDAT RANDOM NUMBER FILE
their Turbobasic predecessor
are the only compilers I have found which seem to be
suitable to use for file encrypting with pseudo-random numbers by my method because with them
the same seed number always creates the same random number sequence which some
other Basics do not seem to do. My general file encryption procedure is
summarized in the next paragraph. I do not know how secure it is but I think it is good enough
for my files on a non internet connected PC even though the random number
generators used may not be secure cryptographically since multiple PRNG
sequences are used for
each file character processed.
First, the selected password PW, root
filename RFN, and file size are used to generate pseudo-random numbers which are
used to transform PW to PW2 and RFN to RFN2. Next, each file
character is transformed to a new one and then encrypted by an XOR with a PW2 encryption key which
is modified after each usage with a random number which depends on RFN2, file
character position, and file size. The encrypted characters are collected into groups of 8 to
form 64 bit quad-words which are then subjected to a bit rotation by the value
of another random number prior to storage in the PW secured encrypted
file so that each character in this file does not correspond to a character in
the same position in the original file .
Then the encrypted file can be used as the source file in another file
encryption cycle up to 99 cycles.