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Some substitution ciphers are created by using a
random cipher alphabet rather than just a shift.
The sender and recipient can communicate as long as they know the
cipher alphabet. The weakness in this system is that the English
language is structured and each letter appears with a certain frequency.
This means that the cipher letter will appear with the same frequency.
Here are the letters of the alphabet with their associated percentage
frequencies in the English language:
| A |
B |
C |
D |
E |
F |
G |
H |
I |
J |
K |
L |
M |
| 8.2 |
1.4 |
2.8 |
3.8 |
13.1 |
2.9 |
2.0 |
5.3 |
6.3 |
0.1 |
0.4 |
3.4 |
2.3 |
| N |
O |
P |
Q |
R |
S |
T |
U |
V |
W |
X |
Y |
Z |
| 7.1 |
8.0 |
2.0 |
0.1 |
6.8 |
6.1 |
10.5 |
2.5 |
0.9 |
1.5 |
0.2 |
2.0 |
0.1 |
Remember that this is an average frequency and short messages may
not contain these exact frequencies.
The message below has been encrypted using a random cipher alphabet.
Use the frequencies above as a guide to recovering the plaintext
letters and once you have a few then guess some common English words
that fit around these letters.
| Cipher: |
ZBDDH QWBPQ KHBTM ALBKM WOCLM ESBEE |
| Plain: |
|
| Cipher: |
JOBXE MWOPK BIXBW TUJWJ DUEME ZBLQA |
| Plain: |
|
| Cipher: |
BUQXL JNBPQ XWHQX KTQHB YKBJV MWOAJ |
| Plain: |
|
| Cipher: |
OBEMW PQKSJ CMNBJ WHLJN BYBBW JYDBC |
| Plain: |
|
| Cipher: |
QZQKV CLKQX OLCLB AXRRD BEAKQ NMHBH |
| Plain: |
|
| Cipher: |
CLJWV UQXPQ KNMEM CMWOQ XKZBY EMCB |
| Plain: |
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Use the table below to help you record the frequencies of the cipher
text letters. Use these frequencies to help guess at the plain text
letter associated with each cipher text letter:
| Cipher: |
A |
B |
C |
D |
E |
F |
G |
H |
I |
J |
K |
L |
M |
| Plain: |
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| Frequency: |
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| Cipher: |
N |
O |
P |
Q |
R |
S |
T |
U |
V |
W |
X |
Y |
Z |
| Plain: |
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| Frequency: |
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Answers
Can't work it out? A solution page
is available.
 Top
of page
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