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On the Use of One-Time Pad Encryption
| (Stormy, please move this to /cyb/)
| We begin with simple alphabetic substitution which is the basis of our code. Each letter in the alphabet has a number. A=1, B=2,..Z=26.
For example the word "LENORE" becomes "12 5 14 15 18 5"
| (Oh shit this was supposed to be in /cyb/!)
| It is necessary, before we encrypt, to create the pad from a lengthy sequence of random letters. This is our key, which belongs to the encryptor and the message's intended recipients. Like this:
AXYBAXQARDGG
The string is split into pairs:
AX YB AX QA RD GG
Using the previously discussed substitution, we convert the letter pairs into 4 digit groups:
0124 2502 1701 1804 0707
Next, we encrypt our plaintext ("LENORE" in this example) with the identical method:
LE NO RE
1205 1415 1805
|
Now we consult the pad. With each new message communicated, a 4digit group is crossed off, as such:
0124 2502 1701 1804 0707 0320
A particularly lengthy pad can be used for many messages, or even shared by both parties in a conversation. This example is too diminutive for practical use but serves our intents.
Continuing, the next sequence in the pad (2502) is added to our text:
2502 1205 1415 1805
| We then align our message with the four numbers from the pad, and add all but the first 4 digits. It is important not to carry the ones! Extra digits are lost. As such:
2502 1205 1215 1805 (LENORE)
2502 1701 1804 0707 (key)
2502 2906 2018 1502 (cyphertext)
The result is cyphertext, the message which is to be sent.
| To decipher, compare the cyphertext to the key, aligning the first four digits, and subtract. (Do not borrow the ones! 4-5 is 9, for example, because 14-5=9. But the 10 is not taken from the digit to the left.)
Example:
---- 2502 2906 2219 1502 (ct)
0124 2502 1701 1804 0707 (pad)
---- ---- 1205 1415 1805 (text)
Convert the numbers back to letters:
12 05 14 15 18 05
L E N O R E
I shall summarize below:
| Create the pad:
>AXYBAXQARDGG
Split into pairs:
>AX YB AX QA RD GG
Letters to numbers:
>0124 2502 0124 1701 1804 0707
Copy and distribute the pad.
Write the message:
>LENORE
Split into pairs
>LE NO RE
Letters to numbers:
>1205 1415 1805
From the key, remove the leftmost group:
> 0124 2502 0124 1701 1804 0707
Apply the next group to the message:
>2502 1205 1415 1805
Align the left group with the key, and add:
>2502 1205 1415 1805
>2502 0124 1701 1804 0707
| >2502 1205 1415 1805 (text)
>2502 0124 1701 1804 0707 (key)
>2502 1329 2116 2609 (resulting cyphertext)
DON'T CARRY THE ONES
The cyphertext is now:
>2502 1329 2116 2609
To decode...
Align and subtract the key from the cyphertext:
>2502 1329 2116 2609 (cyphertext)
>2502 0124 1701 1804 0707 (key)
>---- 1205 1415 1805 (result)
WHEN YOU BORROW A TEN, DON'T CHANGE THE LEFT DIGIT
Number pairs to letters:
>LE NO RE
Combine:
>LENORE
| (My examples are error-ridden in the main text but the summary examples are correct. Sorry.)
-Poe
##Janitor:Stormy##
| Done.
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| I have taken it upon myself to explain to those who wish to use it, a cryptographic method, whose decipherability may slow and confound the intellect of even quantum decryption machines, yet simple enough to use without the application of cryptographic software. It is the one-time pad. So reliable is this archaic method it is the ancestor of modern code, and if one wishes to be heard in secret on Danger/u/ there is no better method. I shall instruct you below: