What is meant by cryptography ? • Its Greek word
• Crypto means “ Secret”
• Graphie means “ Writing “
Why Cryptography ? • To convert the plain text to unreadable text
What is need of Cryptography ?
To secure the Sensitive Information
• Username – Password
• Credit Card Number etc..
CRYPTOGRAPHY COMPONENT
Cryptanalysisbasic component of cryptography is a cryptosystem
Cryptanalyst • Person working for unauthorized interceptor
Cryptographer
• Person working for legitimate sender or receiver
Cryptology
• encryption and decryption
Cryptosystem A cryptosystem is a 5-tuple ( , D , M , K , C)
• M is the collection of plaintexts
• K is the set of keys
• C is the set of cipher texts
o = K → C is the set of encipher (encryption)o D = C K → M is the set of deciphering (decryption)
How it works ?
Note • Plaintext M : collection of original messages
• Cipher text C : set of messages in encrypted form
Cryptosystem
Encryption Decryption
• Process of encoding (enciphering / encryption ) a message
• Process of decoding (deciphering or decryption) an encrypted message to its original form.
securesender
securereceiver
channel data, control messages
data data
Alisa Kishan
Trudy
CRYPTOGRAPHY
CRYPTOGRAPHY
SYMMETRIC-KEY
CRYPTOGRAPHY
ASYMMETRIC-KEY
CRYPTOGRAPHY
Types of Cryptosystems Symmetric Key Cryptosystems
• Also called single-key cryptosystems
• M = D ( K , E ( K , M ) )
• The encryption key and decryption key are the same
Symmetric Cryptosystems Basic techniques for classical ciphers (Encryption)
Substitution
Transposition
Mono-alphabetic
Poly-alphabetic
Stream
• One letter is exchanged for another
• The order of the letters is rearranged Classical ciphers
• Letters of the plaintext alphabet are mapped into other unique letters
• Letters of the plaintext alphabet are mapped into letters of the cipher text space depending on their positions in the text
• Key stream is generated and used to encrypt the plaintext (Symmetric Key Algorithms)
Transposition
Example :-
T 5 T RH 3 H C E EE 1 I E T GK 4 S S M AE 2 I A E SY 6 S S
TRHCEEIETGSSMAIAEASSCipher-Text :-
Refer (by key): IETGIAESHCEESSMATRSS
Columnar
• IEEIRSHSMESCSTATGSEA
T H E K E Y5 3 1 4 2 6
T H I S I SA S E C R ET M E S S AG E
Types of Cryptosystems Asymmetric cryptosystem
• M = D (Kd , E (Ke , M ) )
• The encryption key and decryption key are not the same• Kd ≠ Ke
Asymmetric Key Cryptosystem (Public Key Cryptosystem)
Uses public and private keys
• Public key for encryption• Private key for decryption
Examples
• RSA
• Trapdoor one-way function
• Elliptical curve cryptography
RSA Principle Developed by Ron Rivets , Adi Shamir, and Leonard Adleman. (MIT, 1977)
C = me mod (pq)
• P , q : any two large prime numbers (more than 512 bits)
• e: public key
• d: private key
• Knowing C and e, it is “infeasible” to calculate m without knowing d , p and q
• Knowing d, p and q, it is easy to find the original plaintext message m = Cd mod (pq)
RSA Principle
{m, e, p, q; C= me mod(pq)}
{C, e, p, q; m=Cd mod(pq)}
Sender
Intruder
Receiver
{C, e}
What is Steganography?What is Steganography?
• STEGANOS – “Covered”• GRAPHIE – “Writing”
Its Greek Words:
Steganography is about Hiding messages Digital Applications of Steganography
• Can be hidden in digital data - MS Word (doc)
- Web pages (html) - Sound files (mp3, wav, cda)- Video files (mpeg, avi)
- Digital images (bmp, gif, jpg) Today, steganography is used primarily
to protect digital rights
• “watermarking” copyright notices
• “fingerprinting” a serial ID
History of History of SteganographySteganography Chinese silk balls
Invisible ink-jet technology
Microdots Easter eggs
Hiding a message within a text Shift some words by one point/pixel
- Shifted words (or their first letters) make the sentence Use different fonts
- Letter by letter or word by word
A Real ExampleA Real Example During WW2 the following cipher
message was actually sent by a German spy “Apparently, neutral’s protest is
thoroughly discounted and ignored. Isman hard hit. Blockade issue affect pretext for embargo on by products, ejecting suets and vegetable oils.”
Hidden Message
• “ Pershing sails from NY June 1”
ModernModern Steganography Steganography
Hiding one message within another (“container”)
Most containers are rich media
• Images , audio, video ,mp3 etc.
Copyright notices embedded in digital art
• Prove ownership
Digital cameras EXIF tags
• Not secretive, but hidden from the eyez• Embed info such as camera type, date, shutter
speed , focal length,..
Similarly , possible to embed messages in invisible parts of html pages
Steganography Steganography SystemSystem
ComparisonComparisonCryptography
C = Ek (P) Plain text
P = Dk (C)
Key
Steganography
secret message
cover image
f Stego message
f Ciphertext
Hiding a Message in an ImageHiding a Message in an ImageOriginal Picture Embedded picture
