(Nearly) Unbreakable KeyFile Encryption
The way the encryption works is simple. You simply get the ASCII number for each character and add a random number to it. If the resulting number is greater than 999, I drop the first digit to keep all code numbers at 3 charaters. I add the first char back when I decrypt whenever the decryption would result in a negative ASCII number.
In this example, you can create a field called "myText" where you type the message to be encrypted. After running encodeMyText you can copy the encoded text and paste it into your message for transmission. At the receiving end, it is important that *just* the coded message is pasted back into the field for decryption. This is because, the first part of the message contains the starting place for using the random number file to encode/decode the data.
By incrementing the starting number each time to the place where you last left off, the same numbers in the keyFile are never used again. This is defined as a "one time pad." The encryption is unbreakable (even by NSA). To maintain the intergrity of the code, you might want to have a different random number file for each direction you will be sending encrypted messages. For example, if Bob sends a message to Jane, he might wish to encode it with keyFile A. When Jane receives the message, she will decode it because she also has a copy of keyFile A on her computer. However, if Jane wants to send a message back to Bob, she will encode it using keyFile B. Bob also has a copy of keyFile B so he can decode her message. By each user having their own keyFile for encryption, the chance of re-using numbers from one file is eliminated. (For instance, if Bob and Jane both wrote messages to each other at the same time using the same keyFile, there would be two messages in existence using the same numbers since the start numbers were not incremented sequentially.) In my sample, I used an "A" to indicate the start of the encrypted message. If Jane encrypts her message using keyFile B, she could indicate this by using a "B" instead of an "A." Your decryption handler could then note this change in order to decode the message using the proper keyFile.
If anyone is interested in reading about codes and cyphers, I recommend an excellent book by David Kahn called "The Codebreakers." There is also an excellent recent book called "The Code Book" by Simon Singh.
Hope this helps.
Philip Chumbley ------------------------------------------------------------------------------
# myNumberFile is the file of random numbers which constitutes my keyFile # myPointerFile stores the starting point for the next encryption of text on generateNumbers # This handler will generate a keyFile containing 10,000 random numbers put empty into myNum repeat 10000 put random(10) - 1 after myNum end repeat open file myNumberFile for write write myNum to file myNumberFile close file myNumberFile # Set the pointer to the start of the file put 1 into tStart open file myPointerFile for write write tStart to file myPointerFile close file myPointerFile beep end generateNumbers on encodeMyText # Takes text from field "myText" and encodes it and puts it back into the field put field myText into tText # Get the starting point open file myPointerFile for read read from file myPointerFile until eof close file myPointerFile put it into tStart put tStart into tStart0 # Read in the keyFile (your random file) open file myNumberFile for read read from file myNumberFile until eof close file myNumberFile put it into myKey # Encrypt the text put empty into cipherText # cipherText is the encyrpted message repeat for each char c in tText put char tStart to (tStart + 2) of myKey into cNum add 3 to tStart put charToNum(c) + cNum into charCodeNumber if the number of chars in charCodeNumber = 4 then delete char 1 of charCodeNumber # Save only the last three digits if the number of chars in charCodeNumber = 1 then put "00" & charCodeNumber into charCodeNumber if the number of chars in charCodeNumber = 2 then put "0" & charCodeNumber into charCodeNumber put space & charCodeNumber after cipherText end repeat # You must pass the starting point along with the cipherText put tStart0 & "A" & cipherText into field "myText" # Save the new starting point open file myPointerFile for write write tStart to file myPointerFile close file myPointerFile end encodeMyText on decodeMyText # Takes text from field 'myText" and decodes it and puts it back into field "myText" put field "myText" into tText # Read in the key open file myNumberFile for read read from file myNumberFile until eof close file myNumberFile put it into myKey # Get the starting point get offset("A",tText) put char 1 to (it - 1) of tText into tStart delete char 1 to it of tText # Decode the text put empty into plainText repeat for each word i in tText put i into ii put char tStart to (tStart + 2) of myKey into cNum add 3 to tStart if cNum > ii then add 1000 to ii put numToChar(ii - cNum) after plainText end repeat put plainText into field "myText" # Save the new starting point open file myPointerFile for write write tStart to file myPointerFile close file myPointerFile end decodeMyText
Posted 4/9/2003 by Philip Chumbley to the MetaCard List (See the complete post/thread)