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CRYPTOGRAPHY
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Shray Jali
CRYPTOGRAPHYCryptology is the science of secure communications
Formed from the Greek words kryptós, "hidden", and logos, "word".
Cryptography is a framework of methodologies used to ensure the CIA triad for our information
C –Confidentiality I –Integrity A -Authenticity
Cryptography was known anciently as Encryption which means: Hiding the information from unauthorized entities.
It could be implemented manually, mechanically or even electronically
ENCRYPTIONProcess by which a message is transformed into another message using a mathematical function and a special encryption password.
If we are using symmetric encryption, then we will encrypt the clear message with one key and decrypt it with the same key
SYMMETRIC ENCRYPTION
We will use 9 different private keys for achieving bidirectional communication between XYZ and ABC
We need to define a way by which we can exchange these private keys in a secure manner between distant entities
DES, 3DES, Blowfish, IDEA, RC5, Safer, Serpent and AES are the well known symmetric encryption algorithms
If we are using asymmetric encryption, then we will encrypt the clear message with one key and decrypt it with a different key
ASYMMETRIC ENCRYPTION
ASYMMETRIC ENCRYPTION
ABC and XYZ have their public keys distributed over each other, anyone needs to talk to the other will use the other’s public key to encrypt the traffic and the other will use his own private key to decrypt the traffic, X will use A’s public key to encrypt clear traffic A will receive the cipher to decrypt it using his own private key
RSA is the famous asymmetric key encryption algorithm
EARLY CRYPTOGRAPHY3500 BC: Sumerians
Cuneiform writings
1900 BC: Egypt
EARLY CRYPTOGRAPHY
Substitution cipherUsed by Hebrew
60 –50 BC: Julius Caesar
Shift letters by X positions
E.g. X = 3: A -> D, B -> E, C ->F, ..
500- 600 BC 486 BC: Greece
MEDIEVAL CRYPTOGRAPHY1845: Morse code 1918: The ENIGMA
26 letter keyboard for input & each lamp for a key
“Scrambler”
MEDIEVAL CRYPTOGRAPHY
Substitution cipher substitutes each letter by another letter to diguise it
plain text: 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
Cipher text: q w e r t y u i o p a s d f g h j k l z x c v b n m
Transposition CipherThe Ciphertext is formed by re-arranging the Plaintext in the form of a matrix and then transposing it.
MODERN CRYPTOGRAPHY
1918: ADFGVX CipherA D F G V X
A S U B J E C
D T A D F G H
F I K L M N O
G P Q R V W X
V Y Z 0 1 2 3
X 4 5 6 7 8 9
N E T W O R K I N G
FV
AV
DD
GV
FX
GF
FD
FA
FV
DV
MODERN CRYPTOGRAPHY
1976: Diffie-Hellman Key Exchange
Private key: This key must be know only by its owner.Public key: This key is known to everyone
MODERN CRYPTOGRAPHY
1977: RSA: Rivest, Shamir & Adleman Algorithm
• Both public and private key are interchangeable
• Variable Key Size (512, 1024, or 2048 bits)
• Most popular public key algorithm
MODERN CRYPTOGRAPHY
1991: Pretty Good Privacy
e-mail security
Uses a block cipher called IDEA
Uses Digital Signatures
Uses Web Trust
E.g. X.509 certificates in SSL
MODERN CRYPTOGRAPHY
Stream CiphersGenerates a keystream & combines with plaintext to form ciphertext, e.g. RSA’s RC4Suitable for online encryption of data, e.g. Encrypting Voice CommsMuch faster than block ciphers for online work
Block Ciphers Symmetric-key encryption algorithm that changes a fixed length of
block text into same length of Cipher text Encryption works by means of key and Decryption is the reverse of
encryption process using the same key
The Data Encryption Standard (DES) and the Advanced Encryption Standard (AES) are block cipher designs which are used across a wide range of applications, from ATM encryption to e-mail privacy and secure remote access
They use different keys for encryption and decryption.
Encryption operates on plaintext using the encryption key and the modulus to produce cipher text
Decryption operates on cipher text using the decryption key and the modulus to produce plaintext
MODERN CRYPTOGRAPHY
Public key cryptography
Quantum Cryptography
relies on the laws of physics to ensure that eavesdroppers are unable to successfully gain access to the key while it is in transit
DES64-bit Plain text
Initial transposition
Iteration 1
Iteration 2
Iteration 16
32-swap
Inverse transposition
64-bit cipher text
HASHINGTo ensure the integrity of a message
Hashing is an irreversible process with no keys, the clear message is the only input for the hashing process
MD5 and SHA are the most used hashing algorithms , SHA is more secure than MD5
HASHING
They take a message of any length as input, and output a short, fixed length hash which can be used in a digital signature.
MD4 is a long-used hash function which is now broken; MD5, a strengthened variant of MD4, is also widely used but broken in practice
The U.S. National Security Agency developed the Secure Hash Algorithm series of MD5-like hash functions: SHA-0 was a flawed algorithm that the agency withdrew; SHA-1 is widely deployed and more secure than MD5, but cryptanalysts have identified attacks against it
DIGITAL SIGNATURE It is a mechanism that ensures that the data is received from a secure and a known source.
Document to be signed is sent through a complex mathematical computation that generates a hash.
Hash is encoded with the owner’s private key then stored.To prove future ownership, stored hash is decoded using the owner’s public key and that hash is compared with a current hash of the document.If the two hashes agree, the document belongs to the owner.
Sender
Original Message
Scrambled Message
Scrambled Message
Private Keysender
Original Message
Receiver
Public Keysender
InternetDigital
Signature
DIGITAL SIGNATURE Symmetric key signature
Public key signature
Shra
y
A, KA ( B, RA, t, P)
Sir
KB ( a, RA, t, P, Ksir ( A,t, P)) Sum
it
Shray’s pvt keyDA
Sumit’s public keyEB
Sumit’s pvt keyDB
Shray’s public keyEA
P P
DA(P) DA(P)EB(DA(P))
SHRAY’s COMPUTER SUMIT’s COMPUTER
World Wide Web transactions
Virtual private networks
Electronic mail
Client-server applications
Banking transactions
DIGITAL CERTIFICATESCertificates are issued by a certificate authority (CA). A CA is either specialized software on a company network or a trusted third party.
Applications of digital certificates
ADVANTAGES OF CRYPTOGRAPHYConfidentiality
Authentication
Data integrity
Availability
Non-repudiation
Access control
Anonymity
APPLICATIONS OF CRYPTOGRAPHY
Military and diplomatic services
Protecting confidential company information, telephone calls
e-business
e-lottery
e-transactions