Traditional Symmetric Key Ciphers Prepared By: Shaikh Amrin
3.traditional symmetric key ciphers
Jul 28, 2015
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Traditional Symmetric Key
Ciphers
Prepared By: Shaikh Amrin
Symmetric Key Cipher
Transposition Cipher
Substitution Cipher
Replace one char with another char in cipher text
Reorder the position of the char of plaintext
Substitution CipherSymmetric Key
Cipher
Transposition Cipher
Substitution Cipher
Mono alphabetic Cipher
Poly alphabetic Cipher
One plaintext char will replace with only one char in cipher text1. Additive2. Multiplicative3. Affine
One plaintext char will replace with many char in cipher text1. Auto key 2.
Vigenere3. Hill 4.
Vernam5. Rotor
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 z0 1 2 3 4 5 6 7 8 9 1
011
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Monoalphabetic Cipher
Additive cipher
Plain text: what
Key: 20Encryption
Cipher Text: qbun
Key: 20Decryption
Plain text: what
PT: w 22 22+20=42%26=16
CT: q 16-20=-4%26 = 22
PT: w
PT: h 7 7+20=27%26=1
CT: b 1-20=-19%26=7
PT: h
PT: a 0 0+20=20%26=20
CT: u 20-20=0%26=0
PT: a
PT: t 19 19+20=39%26=13
CT: n 13-20=-7%26=19
PT: t
Also known as shift or caesar cipherBrute Force or statistical attacks are possible to cryptanalyse
Multiplicative Cipher
Plain text: what
Key: 21Encryption
Cipher Text: qbun
Key: 21-1=5Decryption
Plain text: what
PT: w 22 22*21=462%26=20
CT: u 20*5=100%26 = 22
PT: w
PT: h 7 7*21=147%26=17
CT: r 17*5=85%26=7
PT: h
PT: a 0 0*21=0%26=0 CT: a 0*5=0%26=0 PT: a
PT: t 19 19*21=399%26=9
CT: j 9*5=45%26=19
PT: t
Number Inverse
1 1
3 9
5 21
7 15
9 3
11 19
15 7
17 23
19 11
21 5
23 17
25 25
Affine cipher
Plain text: what
Key pair: (21,3)Encryption
Cipher Text: xudm
PT: w 22 22*21=462%26=20+3=23%26=23
CT: x
PT: h 7 7*21=147%26=17+3=20%26=20
CT: u
PT: a 0 0*21=0%26=0+3=3%26=3 CT: d
PT: t 19 19*21=399%26=9+3=12%26=12
CT: m
Cipher Text: xudm
Key pair: (21-1,3)Decryption
Plain text: what
CT: x 23-3=20%26=20*5=100%26 = 22
PT: w
CT: u 20-3=17%26=17*5=85%26=7 PT: h
CT: d 3-3=0%26=0*5=0%26=0 PT: a
CT: m 12-3=9%26=9*5=45%26=19 PT: t
Polyalphabetic Cipher
Autokey CipherPlainText
W H A T I S T H I S
v1 22 7 0 19 8 18 19 7 8 18
v2 9 22 7 0 19 8 18 19 7 8(v1+v2)%26
5 3 7 19 1 0 11 0 15 0
CipherText
f d h t b a l a p a
Plaint text char:I is replaced with b,pt is replaced with t,l
Cipher text char:a is replaced from s,h of plain text
Playfair CipherA M R I/J N
B C D E F
G H K L O
P Q S T U
V W X Y Z
create a pair of two char from plaintext.
Conditions:1. No one pair contain same
characters. If yes then add bogus char.
2. All pairs must be of 2 length.
Rules:Let us consider i1=1st char’s row
number, j1=1st char’s column number,i2=2nd char’s row number, j2=2nd char’s column number.
3. If i1=i2 cipher will be (i1,j1+1)(i2,j2+1)
4. If j1=j2 cipher will be (i1+1,j1)(i2+1,j2)
5. Else cipher will be (i1,j2)(i2,j1)
H E L L O
H E L X L O
L C K Y O G
O H H
O H H X
G K K W
Vigenere CipherEncryption
S H E I S L A Z Y
18 7 4 8 18 11 0 25 24
2 3 1 4 2 3 1 4 2
20 10 5 12 20 14 1 3 0
U K F M U O B D A
Decryption
U K F M U O B D A
20 10 5 12 20 14 1 3 0
2 3 1 4 2 3 1 4 2
18 7 4 8 18 11 0 25 24
S H E I S L A Z Y
Hill Cipher
S H E
I S L
A Z Y
Plain Text: she is lazyAdd z to fill matrix
18 7 4
8 18 11
0 25 24
Key Matrix is:
2 1 1
1 1 2
1 0 2
Cipher Text is: Plain Text * Key %26
21 25 14
19 0 14
23 25 20
2 1 1
1 1 2
1 0 2
18 7 4
8 18 11
0 25 24
18 8 9
0 1 25
17 9 9
Inverse Key Matrix is:
18 8 9
0 1 25
17 9 9
Plain Text is: Cipher Text * Key-1 %26
21 25 14
19 0 14
23 25 20
18 7 4
8 18 11
0 25 24
S H E
I S L
A Z Y
One Time Pad or Vernam Cipher
Encryption
S H E I S L A Z Y
18 7 4 8 18 11 0 25 24
2 3 1 4 5 13 7 6 2
20 10 5 12 23 24 7 5 0
U K F M X Y H F A
Decryption
U K F M X Y H F A
20 10 5 12 23 24 7 5 0
2 3 1 4 5 13 7 6 2
18 7 4 8 18 11 0 25 24
S H E I S L A Z Y
Rotor Cipher
Plain text: beeCipher Text: BCA
Enigma Machine
• Enter C• Stecker: C to S• S permuted to Z by
rotors/reflector• Stecker: Z to L• L lights up
Transposition CipherSymmetric Key
Cipher
Transposition Cipher
Substitution Cipher
Mono alphabetic Cipher
Poly alphabetic Cipher
One plaintext char will replace with only one char in cipher text1. Additive2. Multiplicative3. Affine
One plaintext char will replace with many char in cipher text1. Auto key 2.
Vigenere3. Hill 4.
Vernam5. Rotor
Keyed Transposition Cipher
Keyless
Transposition Cipher
Keyless Transposition Cipher
Rail Fence CipherPlain Text
S H E I S L A Z Y
Row1 S E S A Y
Row2 H I L Z
Cipher Text
S E S A Y H I L Z
Cipher Text
S E S A Y H I L Z
Row1 S E S A Y
Row2 H I L Z
Plain Text
S H E I S L A Z Y
S H E
I S L
A Z Y
PT: Sheislazy
CT: siahszely
Keyless Permutation
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
0 1 2 3 4 5 6 7 8 9 10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
2 7 9 0 21
24
12
1 10
8 3 5 13
15
16
14
18
4 6 11
17
22
25
19
23
20
c h j a v y m b k i d f n p q o s e g l r w z t x u
Keyed Transposition Cipher
Encryption
S H E I S L E A R N I N G
S H E I S L E A R N I N G Z Z
3 1 4 5 2 3 1 4 5 2 3 1 4 5 2
E S I S H A L R N E G I Z Z N
E S I S H A L R N E G I Z Z N
Key
3 1 4 5 2
Decryption
E S I S H A L R N E G I Z Z N
E S I S H A L R N E G I Z Z N
3 1 4 5 2 3 1 4 5 2 3 1 4 5 2
S H E I S L E A R N I N G Z Z
S H E I S L E A R N I N G Z Z
Key
3 1 4 5 2
Keyed Columnar Transposition Cipher or Columnar Transposition
S H E I S
L E A R N
I N G Z Z
Plain Text: she is learning
3 1 4 5 2
E S I S H
A L R N E
G I Z Z N
Cipher Text: eagsliirzsnzhen
Cipher Text: eagsliirzsnzhen
E S I S H
A L R N E
G I Z Z N
S H E I S
L E A R N
I N G Z Z
Key Inversion in Transposition Cipher
2 6 3 1 4 5 Encryption Key
1 2 3 4 5 6 Index
1 2 3 4 5 6 Index
2 6 3 1 4 5 Key
4 1 3 5 6 2 Index=Decryption Key
1 2 3 4 5 6 Sorted key
Stream and Block CipherStream Cipher Block Cipher
Encryption & Decryption are done on Single symbol at a time
A group of plain text symbol of size m (m>1) are encrypted together and creates group of cipher text together of same size.
We are having key stream
Ex: Additive Cipher, monoalphabetic substitution Cipher, Vigener Cipher
Ex: playfair Cipher,Hill Cipher, Polyalphabetic cipher
Each character in the cipher text block depends on all characters in plain text.
THANK YOU
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