shoulderslyrical_099afef0
-
5104
-
44e3
-
a432
-
55c72a7b6bcd.doc
11/21/2013
IDEAS & VALUES
:
Cryptography
Frequency distribution/ tally
Problem
solving
Percent
Logic
Teamwork
PRE
䅃T䥖䥔I
:
Content
Students will decipher an encoded text using letter frequencies.
Cryptography
(from Gree
k
kryptos,
“hidden”, and
graphein,
“to write”)
Process
Review activity objectives and guidelines. Prepare participants to participate in discussion, self assess
and set goals.
Each student should have a copy of the cryptogram, letter freq
uencies, instructions, and the tally sheet.
(Included in this document below)
Pre
Activity questions:
1) What is the most
used letter? …the least
used letter?
2) How many
t
’s would you expect to find in a paragraph of 100 letters? In a paragraph of 50
0 letters?
3) As a group, vowels account for what percentage of letters used?
4) Which two letters have the most unusual percentages?
5) Are most letters used rarely or frequently?
ACTIVITY
:
Problem
獯汶sn朠慣瑩v楴y㨠
0) Students should work in pairs
or small groups for the decoding. Each group should let the others
know when they have decoded a letter. One or two students with calculators can figure the percents for
the group.
1) Using the coded story, fill in tally marks for the number of times each
letter is used. This gives the
frequency for each letter.
2) Find the
percent
frequency for each letter.
%
Freq
SingleLett
erFrequenc
y
SumOfAllLe
tterFreque
ncies
100
3) Compare the letters with the highest frequencies to the known frequencies for the English language.
This should gi
ve you some letters you can use to start decoding.
4) Remember:
It is also useful to think about short words: a single
letter word is usually
a
or
I
; a double
letter
word is commonly , to , in, as, an and so on.
Think about the two letters that can appea
r next to each other in different places in a word, and
about the single
letter word that would be capitalized in the middle of a sentence.
5) Decipher the cryptogram. Whenever you can deduce a letter, fill in all the other blanks that use the
same coded
letter. You can write the letters in the blank line above the coded message.
shoulderslyrical_099afef0
-
5104
-
44e3
-
a432
-
55c72a7b6bcd.doc
11/21/2013
Opening questions:
Round robin: What was the most difficult part of decoding the message? …or the easiest? Explain.
Core Questions:
Have you ever written or received a
coded message? Explain.
If you did
not
know about letter frequencies, what plan would you use to decode this text?
What is a “Caesar cipher”? Does this coded message use a Caesar cipher? Justify your answer.
If you had to select a strategy to use when
putting an important message into code, would you use the
Caesar cipher? Explain.
Closing:
Can you think of a different way to encode a text that would make it more difficult to decode?
POST
䅃T䥖䥔I
:
Process
(Assess individual and group p
articipation in seminar discussion)
Content
(Extend application of textual and discussion ideas; continuation of pre
avtivity.)
Find out if any kind of code or cryptography is used today and for what purpose.
Writing:
shoulderslyrical_099afef0
-
5104
-
44e3
-
a432
-
55c72a7b6bcd.doc
11/21/2013
Name ______________________________
Cryptogram
Qeshh pho vhsh rkqqkof anvo cq c
qcdih. Noh rcka,“K ikjh ecp.”, coa
noh rcka, “K ikjh b
ehhrh.” Qeh qeksa
noh innjha cq qeh qkph, coa ahbkaha
qn ihcwh qehp qn qehks dskiikcoq
bnowhsrcqkno. “Kg K an onq ihcwh onv,
K vkii ecwh qn ehs c inq pnsh
dcinohl.
shoulderslyrical_099afef0
-
5104
-
44e3
-
a432
-
55c72a7b6bcd.doc
11/21/2013
Name _________________________ Date ________
Ciphertext
Letter
Tally of Letters used in Cryptogram
Letter
Frequency
Percent
Frequency
Plaintext
Letter
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Total:
shoulderslyrical_099afef0
-
5104
-
44e3
-
a432
-
55c72a7b6bcd.doc
11/21/2013
Letter Frequencies for Standard English
Letter
Percent
A
8.2
B
1.4
C
2.8
D
3.8
E
13
F
3
G
2
H
5.3
I
6.5
J
0.1
K
0.4
L
3.4
M
2.5
N
7
O
8
P
2
Q
0.1
R
6.8
S
6
T
10.5
U
2.5
V
0.9
W
1.5
X
0.2
Y
2
Z
0.07
TOTAL
99.97
Enter the password to open this PDF file:
File name:
-
File size:
-
Title:
-
Author:
-
Subject:
-
Keywords:
-
Creation Date:
-
Modification Date:
-
Creator:
-
PDF Producer:
-
PDF Version:
-
Page Count:
-
Preparing document for printing…
0%
Comments 0
Log in to post a comment