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8/4/2019 TSM Crptography
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CRYPTOGRAPHY
8/4/2019 TSM Crptography
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• Cryptology – Science of encryption
• Cryptography
Kryptos-hidden
Graphein- to write
• Cryptanalysis
Obtaining original message from encrypted message
without knowing algorithms or keys.
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• Encryption:
Process of converting original message in to
form that is unreadable to unauthorized
person.
Decryption:
Process of encrypted text message back in tooriginal form.
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Security provided by Encryption
Confidentiality:
Hide information from unauthorizedindividuals either in transit or in storage.
Interception causes loss of messageconfidenttality
Integrity:
It identifies changes of information either intransit or in storage. Modification causes lossof message integrity.
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Accountability :
Enables authentication of the origin of message
and prevents information from repudiating.
Nonrepudiation:
It does not allow sender of message to refute the
claim of not sending that message.
Access Control
Availability
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Physical Cryptography
(Weak keys)
• Substitution Ciphers:
Changing one character/ symbol in to another
Transposition Cipher:
Transposing or scrambling the letters in acertain manner.
Stegnography
Process of hiding one message in another.
Hybrid Systems
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• Substitution Poly alphabatic
A B C D E F G……. Plain Text
J K L M N O P…… Substitution 1
Q R S T U V W….. Substitution 2
Transposition Cipher( Permutation) From right
1-4, 2-8, 3-1, 4-5, 5-7, 6-2, 7-6, 8-3
00100101 01101011
00001011 10111010
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Transposition Ciphers
• Rearrange order of characters(permutation)
• SIMPLE COLUMNAR CIPHER
Using a grid, write plaintexthorizontally, read ciphertext.
vertically.
P launchmissilesnow
launch
missil
esnow
C LMEAISUSNNSOCIWHL
• ATTACK ON COLUMNAR CIPHER Ciphertext has same letterfrequencies as plaintext -> Easy
• MULTIPLE TRANSPOSITION
CIPHERS Pass a plaintext through two ormore transposition ciphers ->Much harder to attack.
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One-time Pad
• Use a random key as long as themessage. Must not reuse the keysequence ever again.
• Both parties must have key sequence
• Hotline between USA and USSR wasrumoured to use a one-time pad.
• Destroy key sequence after use
• Advantages?
• Disadvantages?
• EXAMPLE
Key is number of places to shift
letter
K 321424
P launch
C OCVREL • Suggest a good 1-time pad
function for binary data?
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Transposition Ciphers
• Rearrange order of characters(permutation)
• SIMPLE COLUMNAR CIPHER
Using a grid, write plaintexthorizontally, read ciphertext.
vertically.
P launchmissilesnow
launch
missil
esnow
C LMEAISUSNNSOCIWHL
• ATTACK ON COLUMNAR CIPHER Ciphertext has same letterfrequencies as plaintext -> Easy
• MULTIPLE TRANSPOSITION
CIPHERS Pass a plaintext through two ormore transposition ciphers ->Much harder to attack.
8/4/2019 TSM Crptography
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Steganography
Dear George, 3rdMarch
Greetings to all at Oxford. Many thanks for your
letter and for the Summer examination package.
All Entry Forms and Fees Forms should be
readyfor final dispatch to the Syndicate by Friday
20th or at the very least, I’m told, by the 21st.
Admin has improved here, though there’s room
for improvement still; just give us all two orthree
more years and we’ll really show you! Please don’t let these wretched 16+ proposals destroy
your basic O and A pattern. Certainly this
sort of change, if implemented immediately,
would bring chaos.
Conceal existence ofmessage, e.g. 1stletter of each word,least sig. bit ofgraphic image
Useless once methoddiscovered
Peter Wayner,Disappearing Cryptography , 2nd ed,Morgan Kaufmann,2002
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Steganography **
Dear George, 3rdMarch
Greetings to all at Oxford. Many thanks for your
letter and for the Summer examination package.
All Entry Forms and Fees Forms should be
ready for final dispatch to the Syndicate by Friday
20th or at the very least, I’m told, by the 21st.
Admin has improved here, though there’s room
for improvement still; just give us all two orthree
more years and we’ll really show you! Please don’t let these wretched 16+ proposals destroy
your basic O and A pattern. Certainly this
sort of change, if implemented immediately,
would bring chaos.
8/4/2019 TSM Crptography
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Moon beans are nice.
Moon Beams Are Nice
on Mo amsBe reA Ce.Ni
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Mathematical Cryptography
• HASH Function
Mathematical algorithms.
Message : this
ASCII Values: 116 104 105 115
Calculated value: 232 202 210 230
Hash value Calculation:
(232+208+210+230)/10
Hash Value: 88
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DES
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• Symmetric Algorithms:
Both ends of an encrypted message have thesame key and processing algorithms.
Secret key is generated which is some timescalled as Private key.
Asymmetric Algorithms:
Two keys to encrypt & decrypt data,
referred as Public Key & Private key.Public key used by sender to encrypt.
Private key is used by receiver to decrypt.
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Steganography **
Dear George, 3rdMarch
Greetings to all at Oxford. Many thanks for your
letter and for the Summer examination package.
All Entry Forms and Fees Forms should be
ready for final dispatch to the Syndicate by Friday
20th or at the very least, I’m told, by the 21st.
Admin has improved here, though there’s room
for improvement still; just give us all two orthree
more years and we’ll really show you! Please don’t let these wretched 16+ proposals destroy
your basic O and A pattern. Certainly this
sort of change, if implemented immediately,
would bring chaos.
8/4/2019 TSM Crptography
http://slidepdf.com/reader/full/tsm-crptography 20/22
Steganography
Dear George, 3rdMarch
Greetings to all at Oxford. Many thanks for your
letter and for the Summer examination package.
All Entry Forms and Fees Forms should be
readyfor final dispatch to the Syndicate by Friday
20th or at the very least, I’m told, by the 21st.
Admin has improved here, though there’s room
for improvement still; just give us all two orthree
more years and we’ll really show you! Please don’t let these wretched 16+ proposals destroy
your basic O and A pattern. Certainly this
sort of change, if implemented immediately,
would bring chaos.
Conceal existence ofmessage, e.g. 1stletter of each word,least sig. bit ofgraphic image
Useless once methoddiscovered
Peter Wayner,Disappearing Cryptography , 2nd ed,Morgan Kaufmann,2002
8/4/2019 TSM Crptography
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