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# 数学代写|密码学代写CRYPTOGRAPHY代考|COMP785 Double Transposition

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## 数学代写|密码学代写CRYPTOGRAPHY代考|Double Transposition

As before, when we encounter an attack on a cipher system, we can think about how to block it and thus create a stronger cipher system. In this case, the weakness is that when we try to form words, we have many rows to work with and can evaluate them as a group as being more or less likely than other possible alignments. To block this, we could use a method known as double transposition. This is demonstrated below.
Example 9
We’ll encipher the following using double transposition with the key FRIEDRICH NIETZSCHE.
YES SOMETHING INVULNERABLE UNBURIABLE IS WITH ME SOMETHING
THAT WOULD REND ROCKS ASUNDER IT IS CALLED MY WILL SILENTLY
DOES IT PROCEED AND UNCHANGED THROUGHOUT THE YEARS
We start off exactly as we did for columnar transposition:
$\begin{array}{llllllllllllllllll}\text { F } & \text { R } & \text { I } & \text { E } & \text { D } & \text { R } & \text { I } & \text { C } & \text { H } & \text { N } & \text { I } & \text { E } & \text { T } & \text { Z } & \text { S } & \text { C } & \text { H } & \text { E } \ \text { Y } & \text { E } & \text { S } & \text { S } & \text { O M } & \text { M } & \text { T } & \text { H } & \text { I } & \text { N } & \text { G } & \text { I } & \text { N V } & \text { U } & \text { L } & \text { N } \ \text { E } & \text { R } & \text { A } & \text { B } & \text { L } & \text { E } & \text { U } & \text { N } & \text { B } & \text { U } & \text { R } & \text { I } & \text { A } & \text { B } & \text { L } & \text { E } & \text { I } & \text { S } \ \text { W } & \text { I } & \text { T } & \text { H } & \text { M } & \text { E } & \text { S O } & \text { M } & \text { E } & \text { T } & \text { H } & \text { I } & \text { G } & \text { T } & \text { H } & \text { A } \ \text { T } & \text { W } & \text { O } & \text { U } & \text { D D } & \text { R } & \text { E } & \text { N } & \text { D } & \text { R } & \text { O C C } & \text { S } & \text { A } & \text { S } & \text { U } \ \text { N } & \text { D } & \text { E } & \text { R } & \mathrm{~ I ~ T ~}\end{array}$
but we place the ciphertext under the key
$\begin{array}{llllllllllllllllll}\text { F } & \text { R } & \text { I } & \text { E } & \text { D } & \text { R } & \text { I } & \text { C } & \text { H } & \text { N } & \text { I } & \text { E } & \text { T } & \text { Z } & \text { S } & \text { C } & \text { H } & \text { E } \ \text { T } & \text { N } & \text { O } & \text { E } & \text { S } & \text { T } & \text { D } & \text { U } & \text { U } & \text { E } & \text { T } & \text { A } & \text { Y } & \text { T } & \text { E } & \text { R } & \text { O } & \text { L } \ \text { M } & \text { L } & \text { I } & \text { L } & \text { D } & \text { G } & \text { S } & \text { B } & \text { H } & \text { U } & \text { R } & \text { I } & \text { E } & \text { G } & \text { I } & \text { H } & \text { O } \ \text { L } & \text { O } & \text { H } & \text { E } & \text { N } & \text { S } & \text { A } & \text { U } & \text { I } & \text { R } & \text { T } & \text { Y } & \text { E } & \text { W } & \text { T } & \text { N } & \text { L } \ \text { O } & \text { H } & \text { H } & \text { B } & \text { M } & \mathrm{~}\end{array}$

## 数学代写|密码学代写 CRYPTOGRAPHY代考|Word Transposition

While transposition is most commonly used on letters (or bits for computerized encryption), it can be done at the level of words. During the U.S. Civil War, the Union enciphered much of its

communications in this manner. As a sample ciphertext, consider the following June 1,1863 dispatch from Abraham Lincoln. ${ }^{15}$
GUARD ADAM THEM THEY AT WAYLAND BROWN FOR KISSING VENUS
CORESPONDENTS AT NEPTUNE ARE OFF NELLY TURNING UP CAN GET
WHY DETAINED TRIBUNE AND TIMES RICHARDSON THE ARE ASCERTAIN
AND YOU FILLS BELLY THIS IF DETAINED PLEASE ODOR OF LUDLOW
COMMISSIONER
GUARD indicates the size of the rectangle and what path to follow for the transposition. In this case, to decipher, the words should be filled in by going up the first column, down the second, up the fifth, down the fourth, and up the third. After GUARD, every eighth word is a null, and is therefore ignored. $.^{16}$ We get
$\begin{array}{lllll}\text { FOR } & \text { VENUS } & \text { LUDLOW } & \text { RICHARDSON } & \text { AND } \ \text { BROWN } & \text { CORRESPONDENTS } & \text { OF } & \text { THE } & \text { TRIBUNE } \ \text { WAYLAND } & \text { AT } & \text { ODOR } & \text { ARE } & \text { DETAINED } \ \text { AT } & \text { NEPTUNE } & \text { PLEASE } & \text { ASCERTAIN } & \text { WHY } \ \text { THEY } & \text { ARE } & \text { DETAINED } & \text { AND } & \text { GET } \ \text { THEM } & \text { OFF } & \text { IF } & \text { YOU } & \text { CAN } \ \text { ADAM } & \text { NELLY } & \text { THIS } & \text { FILLS } & \text { UP }\end{array}$
If transposition were the only protection, we’d be able to read the message now; however, the Union used an extra level of protection-code words:
VENUS = colonel
WAYLAND $=$ captured
ODOR = Vicksburg
NEPTUNE $=$ Richmond
$\mathrm{ADAM}=$ President of the U.S.
NELLY $=4: 30 \mathrm{pm}$

## 数学代写|密码学代写CRYPTOGRAPHY代考|Word Transposition

16我们得到
FOR VENUS LUDLOW RICHARDSON AND BROWN CORRESPONDENTS OF THE TRIBUNE WAYLAND

VENUS =
WAYLAND上校 $=$ 捕获

ADAM $=$

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