- WELCOME TO A LESSON ON 
TRANSPOSITION CIPHERS.
ONE APPROACH TO CRYPTOGRAPHY 
IS USE OF A TRANSPOSITION CIPHER
WHERE A TRANSPOSITION CIPHER 
IS ONE IN WHICH
THE ORDER THE CHARACTERS IS 
CHANGED TO OBSCURE THE MESSAGE.
AN EARLY VERSION 
OF A TRANSPOSITION CIPHER
WAS AN -- IN WHICH PAPER 
WAS WRAPPED AROUND A STICK
AND THE MESSAGE WAS WRITTEN.
ONCE UNWRAPPED, THE MESSAGE 
WOULD BE UNREADABLE
UNTIL THE MESSAGE WAS WRAPPED
AROUND A SIMILAR SIZED STICK 
AGAIN.
ONE MODERN TRANSPOSITION CIPHER
IS DONE BY WRITING 
THE MESSAGE IN ROWS,
THEN FORMING THE ENCRYPTED 
MESSAGE
FROM THE TEXT IN COLUMNS.
AS AN EXAMPLE, 
LET'S ENCRYPT THE MESSAGE,
"MEET AT 3:00 P.M. 
TODAY AT THE USUAL LOCATION"
USING ROWS OF SIX CHARACTERS.
SO IF EACH ROW HAS SIX 
CHARACTERS,
THAT MEANS WE SHOULD FORM 
A TABLE WITH SIX COLUMNS,
ONE, TWO, THREE, FOUR, 
FIVE, SIX.
NOTICE HOW EACH ROW 
WILL HAVE SIX CHARACTERS.
NEXT WE'D WRITE THE MESSAGE 
FROM LEFT TO RIGHT
COMPLETING EACH ROW.
NOTICE HERE WE HAVE MEET 
AT 3:00 P.M.
TODAY AT THE USUAL LOCATION.
AND NOW TO ENCRYPT THE MESSAGE,
WE'D WRITE THE CHARACTERS 
USING THE COLUMNS.
SO USING THE COLUMNS,
THE ENCRYPTED MESSAGE OR ENCODED 
MESSAGE WOULD BE
M, T, M, "A,", S, C, WHICH WE 
SEE HERE, E, H, T, T, U, "A,"
WE SEE HERE, E, R, O T, "A," 
T HERE, T, E, D, H, L, "I"
HERE "A," E, "A," E, L, O, 
AND FINALLY T, P, Y, U, O, N.
BUT THERE IS ONE MORE THING.
THE SPACES WOULD BE REMOVED 
OR REPOSITIONED
TO HIDE THE SIZE OF THE TABLE 
USED
SINCE THAT IS THE ENCRYPTION KEY 
IN THIS MESSAGE.
SO WE WOULDN'T LEAVE IT 
IN THIS FORM HERE
BECAUSE IF LEFT IN THIS FORM,
IT COULD TELL THE MESSAGE 
WAS ENCRYPTED
USING ROWS OF SIX CHARACTERS.
LET'S TAKE A LOOK 
AT ANOTHER EXAMPLE,
LET'S DECRYPT THE MESSAGE GIVEN 
HERE IF IT WAS ENCRYPTED
USING A TABULAR TRANSPOSITION 
CIPHER WITH ROWS OF LINK FOUR.
SO BECAUSE WE KNOW IT WAS FORMED
WITH ROWS OF LINK 
FOUR CHARACTERS,
WE'D FORM A TABLE WITH FOUR 
COLUMNS WHICH WE SEE HERE
BUT BEFORE WE DECRYPT 
THE MESSAGE,
WE DO HAVE TO KNOW HOW MANY ROWS 
THERE WERE.
SO WE'LL FIND THE TOTAL NUMBER 
OF CHARACTERS
WHICH IS 3 x 10 + THESE EXTRA 
TWO ARE 32 CHARACTERS.
WE'RE GOING TO DIVIDE BY THE 
NUMBER OF CHARACTERS PER ROW
WHICH IS FOUR, 
32 DIVIDED BY 4 = 8
WHICH MEANS WE NOW KNOW 
WE'LL HAVE EIGHT ROWS.
SO, ONE, TWO, THREE, FOUR, FIVE, 
SIX, SEVEN, EIGHT.
SO WHEN DECRYPTING A MESSAGE 
USING THIS METHOD,
IT IS IMPORTANT TO ALWAYS FIND 
OUT HOW MANY ROWS WE HAVE
AND NOW BECAUSE THIS WAS FORMED
BY READING THE CHARACTERS OFF 
IN COLUMNS,
WE'LL WRITE THESE DOWN IN COLUMN 
ONE, TWO, THREE AND FOUR.
TO HELP US DO THIS, LET'S COUNT 
OFF EIGHT CHARACTERS,
SO WE HAVE THREE, SIX, SEVEN, 
EIGHT, FOUR, SEVEN, EIGHT,
TWO, FIVE, EIGHT, 
AND THEN EIGHT AGAIN.
SO THE FIRST COLUMN WILL CONSIST 
OF THESE CHARACTERS.
THESE WILL BE IN THE SECOND 
COLUMN,
THESE WILL BE IN THIRD 
AND SO ON.
HERE WE HAVE "A," E, S, E, "A," 
O, O, "I."
HERE WE HAVE T, V, U, "I," N, N, 
N, N,
FOLLOWED BY E, E, R, L, C, F, T, 
E
AND FINALLY 
L, N, V, L, E, R, L, S.
NOW TO DECRYPT THIS, WE'LL READ 
THIS OFF GOING ROW BY ROW.
SO THE ORIGINAL MESSAGE WAS AT 
11, SURVEILLANCE ON FRONT LINES.
AGAIN THE MESSAGE WAS AT 11, 
SURVEILLANCE ON FRONT LINES.
MORE COMPLEX VERSIONS 
OF THIS ROWS AND COLUMN
BASED TRANSPOSITION CIPHER 
CAN BE CREATED
BY SPECIFYING AN ORDER IN WHICH 
THE COLUMNS SHOULD BE RECORDED.
FOR EXAMPLE THE METHOD 
COULD SPECIFY
THAT AFTER WRITING THE MESSAGE 
OUT IN ROWS,
THAT YOU SHOULD RECORD THE THIRD 
COLUMN THEN THE FOURTH COLUMN,
THEN THE FIRST, THEN THE SECOND.
THIS ADDS ADDITIONAL COMPLEXITY 
THAT WOULD MAKE IT HARDER
TO MAKE IT A BRUTE FORCE ATTACK.
TO MAKE THE ENCRYPTION KEY 
EASIER TO REMEMBER,
A WORD COULD BE USED.
FOR EXAMPLE, 
IF THE KEY WORD WAS MATH,
IT WOULD SPECIFY THAT ROWS 
SHOULD HAVE FOUR CHARACTERS EACH
BECAUSE THERE IS FOUR LETTERS 
IN THE WORD.
THE ORDER OF THE LETTERS 
IN THE ALPHABET WOULD DICTATE
WHICH ORDER TO READ 
THE COLUMNS IN.
SINCE "A" THE SECOND LETTER 
IN THE WORD,
IS THE EARLIEST LETTER IN THE 
ALPHABET FROM THE WORD MATH,
THE SECOND COLUMN 
WOULD BE USED FIRST
FOLLOWED BY THE FOURTH COLUMN 
BECAUSE THAT'S H,
THEN THE FIRST COLUMN 
BECAUSE OF THE M,
THEN THE LAST COLUMN 
WOULD BE THE THIRD COLUMN
BECAUSE OF THE T.
LET'S TAKE A LOOK 
AT TWO MORE EXAMPLES.
WE WANT TO ENCRYPT THE MESSAGE 
GIVEN HERE
USING A TABULAR TRANSPOSITION 
CIPHER
WITH ENCRYPTION KEY MAINE,
IF NECESSARY PAD THE MESSAGE 
WITH "A'S."
NOTICE HERE THERE 
ARE FIVE LETTERS IN MAINE,
SO WE BEGIN BY MAKING ROWS 
OF FIVE CHARACTERS
SO WE'LL HAVE FIVE COLUMNS, ONE, 
TWO, THREE, FOUR, FIVE.
NOW WE'LL WRITE THE MESSAGE OUT 
IN ROWS.
SO WE HAVE AT 4, SURVEILLANCE 
ON ENEMY CAMP,
WE HAVE ONE EXTRA CHARACTER HERE 
WE FILL WITH "A"
THAT WAY EACH ROW HAS EXACTLY 
FIVE CHARACTERS.
BUT NOW WE'RE NOT GOING TO READ 
THE ROWS OFF
FROM ROW ONE TO ROW FIVE,
WE'RE GOING TO BASE IT UPON 
THE LETTERS IN THE WORD MAINE.
IF WE ORDER THESE LETTERS 
ALPHABETICALLY
NOTICE "A" 
WOULD BE THE FIRST LETTER
WHICH REPRESENTS COLUMN TWO SO 
WE'LL READ OFF COLUMN TWO FIRST.
THE NEXT LETTER WOULD BE E, 
THE FIFTH LETTER,
SO WE'LL READ OFF COLUMN FIVE 
NEXT.
THE NEXT LETTER IN THE ALPHABET 
WOULD BE "I"
WHICH IS THE THIRD LETTER,
SO WE'LL READ OFF COLUMN THREE 
FOLLOWED BY THE LETTER M
WHICH REPRESENTS THE FIRST 
COLUMN SO THE FIRST COLUMN
WOULD BE READ OFF FOURTH
AND THEN FINALLY N IS THE LAST 
LETTER ALPHABETICALLY
SO THE LAST COLUMN 
WILL BE COLUMN FOUR.
SO WE'LL FIRST READ OFF COLUMN 
TWO, THIS COLUMN HERE,
SO OUR ENCRYPTED MESSAGE 
WILL BE T, S, "I," C, N, "A,"
NEXT WE'LL READ OFF COLUMN FIVE,
SO WE'LL HAVE U, V, "A," N, Y, 
"A," NEXT COLUMN THREE,
SO WE HAVE F, U, L, E, E, M, 
THEN COLUMN ONE
SO WE HAVE "A," R, E, N, E, C 
AND FINALLY COLUMN FOUR.
SO WE HAVE O, R, L, O, M, P.
AND AGAIN WE, 
AGAIN AS OUR LAST STEP,
WE SHOULD REMOVE THE SPACES,
REGROUP THESE LETTERS 
DIFFERENTLY NOT TO GIVE AWAY
HOW THIS WAS ENCRYPTED.
AS OUR LAST EXAMPLE, LET'S 
DECRYPT THE MESSAGE GIVEN HERE
IF IT WAS ENCRYPTED USING A 
TABULAR TRANSPOSITION CIPHER
WITH ENCRYPTION KEY PLAN.
SO THIS TELLS US THAT WE HAVE 
FOUR CHARACTERS PER ROW,
WE HAVE HERE, 
SO WE HAVE FOUR COLUMNS.
NEXT WE HAVE TO DETERMINE HOW 
MANY ROWS
WE WOULD HAVE BASED UPON 
THE NUMBER OF CHARACTERS
WHICH IS 20, SO WE'LL TAKE 20,
DIVIDE BY THE NUMBER 
OF CHARACTERS PER ROW
WHICH IS FOUR, 
AND THEREFORE WE CAN SEE
WE'LL HAVE A TOTAL OF FIVE ROWS 
EACH CONTAINING FOUR CHARACTERS.
SO, ONE, TWO, THREE, FOUR, FIVE
AND NOW WE'RE GOING TO COMPLETE 
THE COLUMNS
USING THESE CHARACTERS BASED 
UPON THE LETTERS IN PLAN.
SO ALPHABETICALLY "A" 
WOULD COME FIRST,
SO WE'LL COMPLETE COLUMN 
3 FIRST.
NEXT WOULD BE THE LETTER L 
SO WE'LL COMPLETE COLUMN TWO,
NEXT WOULD BE N, 
SO WE'LL COMPLETE COLUMN FOUR,
AND THEN FINALLY WE'LL COMPLETE 
THE FIRST COLUMN FOR P LAST.
AND AGAIN BECAUSE EACH COLUMN 
HAS FIVE CHARACTERS,
LET'S BLOCK THIS INTO FIVES
SO WE'D HAVE FIRST FIVE 
CHARACTERS HERE,
THE NEXT FIVE, 
THE NEXT FIVE AND THE LAST FIVE.
THE FIRST COLUMN WE'LL COMPLETE
WILL BE COLUMN THREE 
BECAUSE OF THE "A"
SO NOTICE HOW WE HAVE N, "A," C, 
S, M IN COLUMN THREE.
THE SECOND COLUMN WE'LL COMPLETE 
WILL BE COLUMN TWO
BECAUSE OF THE L, SO WE'LL HAVE 
T, N, "A," "A," "A"
WHICH WE SEE HERE.
THE THIRD WILL BE THE FOURTH 
COLUMN BECAUSE OF THE N,
WE'LL HAVE O, T, K, E, P
AND THEN FOURTH 
WILL BE THE FIRST COLUMN
BECAUSE OF THE P 
WHICH WILL BE "A," O, T, B, C.
AND NOW WE'LL USE THE ROWS 
TO DECRYPT THE MESSAGE.
THE ORIGINAL MESSAGE 
WAS AT NOON, ATTACK BASE CAMP.
UNFORTUNATELY, 
SINCE THE TRANSPOSITION CIPHER
DOES NOT CHANGE THE FREQUENCY 
OF INDIVIDUAL LETTERS,
IT IS STILL SUSCEPTIBLE 
TO FREQUENTLY ANALYSIS
THOUGH THE TRANSPOSITION 
DOES ELIMINATE INFORMATION
FROM LETTER PAIRS.
I HOPE YOU FOUND 
THIS LESSON HELPFUL.
