Cryptography Assignment Help free Sample
The following is a ciphertext:
ZQ GDH LMJ XHBIG JODHAC PD CLUJ XZUJF ZO KLMZV LV L GDHOA RLO, PCJO ECJMJUJM GDH AD QDM PCJ MJVP DQ GDHM XZQJ ZP VPLGV EZPC GDH, QDM KLMZV ZV L RDUJLNXJ QJLVP JMOJVP CJRZOAELG
a) What kind of cipher text is this? Mono- or Poly alphabetic; [Hint: assume one and when that does not work look for the other] [2 points]
We will try online tool
Trying with Poly alphabetic decryption
XZ IOO DEH GJMPY BMMJLJ HV AUWU ERMHO BZ RDEXE NG S YVFXC CSG, HASQ PJBEHDLX NVZ YM SOT HUH VLGW VI EMJX ERIH IR GWDYT NBAJ YVF, ZFX RDEXE BG S JVSSNYEB IHUXA QEGHER NQJRMJGWN
Obliviously it didn’t work, so we will go and try with mono alphabetic decryption.
Trying with Mono alphabetic
ZQ GDH LMJ XHBIG JODHAC PD CLUJ XZUJF ZO KLMZV LV L GDHOA RLO, PCJO ECJMJUJM GDH AD QDM PCJ MJVP DQ GDHM XZQJ ZP VPLGV EZPC GDH, QDM KLMZV ZV L RDUJLNXJ QJLVP JMOJVP CJRZOAELG
IF YOU ARE DUPBY ENOUGH TO HAVE DIVEK IN MARIS AS A YOUNG CAN, THEN WHEREVER YOU GO FOR THE REST OF YOUR DIFE IT STAYS WITH YOU, FOR MARIS IS A COVEALDE FEAST ERNEST HECINGWAY
This did work, we can conclude it is Mono alphabetic text.
b) Describe your cryptanalysis process. List all the steps you went through to decrypt the message. The steps should be in sufficient details so that a reader would be able to decrypt the encrypted text without needing any help from you. [If you find solution online or use online tools please give reference. However, you should describe the steps as if you are working without the tool, (Hint consider starting with the frequency analysis) to get full credit] [If you list partial steps you will get partial credit] [15points]
Letter Frequencies in this ciphertext
As we know from the English analysis, we know most common letters are using in following order
E -> T
So, using above frequency table that we build,
Here J will be replaced with E
D , L or P will be replaced with T
Most common trigraph the is used PCJ which is THE
|
One-Letter Words |
a, I. |
|
Frequent Two-Letter Words |
of, to, in, it, is, be, as, at, so, we, he, by, or, on, do, if, me, my, up, an, go, no, us, am |
|
Frequent Three-Letter Words |
the, and, for, are, but, not, you, all, any, can, had, her, was, one, our, out, day, get, has, him, his, how, man, new, now, old, see, two, way, who, boy, did, its, let, put, say, she, too, use |
|
Frequent Four-Letter Words |
that, with, have, this, will, your, from, they, know, want, been, good, much, some, time |
Replace above character in the cypher text we conclude key pair as
Abc d efghijklmnopqrst uvwxyz -> clear text
Lir x jqacztfnkodbsmvp hueygw -> mapped to
c) State the plain text message in readable form i.e. separating words if required
IF YOU ARE DUPBY ENOUGH TO HAVE DIVEK IN MARIS AS A YOUNG CAN, THEN WHEREVER YOU GO FOR THE REST OF YOUR DIFE IT STAYS WITH YOU, FOR MARIS IS A COVEALDE FEAST ERNEST HECINGWAY
[the solution worked without the help from online tools will be given full credit] [2 pts]
d) List features of the cipher- text that hindered and helped your decryption process. mention of helpful and hindering features [ 6 pts]
And the methodology is mapping the alphabets with key alphabets that is:
The word that help is THE, LIFE, UE respectively
Cryptography Sample 2
Cryptography with Strings and Character Arrays 1.1 Cryptography:
Cryptography is a collection of technique to change the original message to secure a communication between two parties. "This field involves the process of encryption, in which a message, called plaintext, is converted into a scrambled message, called cipher text. It also involves decryption, turning a cipher text back into its original plaintext" (1).
One simple type of encryption is to substitute each letter in the plaintext with another letter e.g. substitute each letter with the letter following it by one, two or any number of letters. If each letter will be substituted with the one after it. A will be substituted by B, B will be substituted by C... and so on. Finally, Z will be substituted with A. :
(Example(1 letter plain text: hi welcome back cipher Text:ij xfmdpnfcbdl
Example(4 letters): plain text: hi welcome back cipher Text: Im aipgsqi fego
1.2 Write a pseudo code (algorithm steps) for an encoder method that takes the plaintext and a number. The number represents how many letters the cipher letter is far from original letter. The algorithm should generate a cipher text for the plaintext by substituting each letter with letter following it by the specified number (5 points) Note: the steps should be written as comments before the next method in the code file.
1.3 Write a method based on your previous answer called encoder that takes a message as plain text and a number. The method should encrypt the message by substituting each letter in the message with the letter following it by the specified number. The method should return the cipher text. (20 point)
encoder(plaintext,number)
ALGORITHM
INPUT: A plaintext and number
OUTPUT: An encoded Text
Step 1: Declare a character variable C, string variable CIPHER,and int i
Step 2: for i=0 to length(plaintext)
2..1 Extract individual characters from the text and store it in the variable {'C'}
2.2 C=C+number
2.3 Append C to CIPHER
Step 3: Print the encrypted text CIPHER
PSEUDOCODE
Begin
string CIPHER=[]
For i = 0 to PLAINTEXT[i] != {'\0'}
C = PLAINTEXT[i]
{'//encrypt for lowercase letter'}
If (C >= 'a' and C <= 'z')
C = C + number
if (C > 'z')
C = C - 'z' + 'a' - 1
done
CIPHER[i] = C
{'//encrypt for uppercase letter'}
else if (C >= 'A' and C <= 'Z')
C = C + number
if (C > 'Z')
C= C - 'Z' + 'A' - 1
done
CIPHER[i] = C
done
done
Print Encrypted message -CIPHER
End
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