Transcript
Cryptography
BY-NISHANT BANSAL
11112030
Overview
Basic Definitions History of Cryptography Cipher Types Cryptography Methods Common Types of Attacks
Definitions -
Cryptology
Cryptography
Cryptanalysis
Steganography
Cryptosystem
Cryptography is everywhere
Secure communication:
–web traffic: HTTPS
–wireless traffic: 802.11i WPA2 (and WEP), GSM, Bluetooth
Encrypting files on disk: EFS, TrueCrypt
Content protection (e.g. DVD, Blu-ray): CSS, AACS
User authentication
… and much much more
History of Cryptography
The first known evidence of the use of cryptography (in some form) was found in an inscription carved around 1900 BC, in the main chamber of the tomb of the nobleman Khnumhotep II, in Egypt.
Around 400 B.C., the Spartans used a system of encrypting information by writing a message on a sheet of papyrus.
Around 100 B.C., Julius Caesar was known to use a form of encryption to convey secret messages to his army generals posted in the war front.
During the 16th century, Vigenere designed a cipher that was supposedly the first cipher which used an encryption key.
At the start of the 19th century when everything became electric, Hebern designed an electro-mechanical contraption which was called the Hebern rotor machine.
The Engima machine was invented by German engineer Arthur Scherbius at the end of World War I, and was heavily used by the German forces during the Second World War.
IBM in early 1970s designed a cipher called Lucifer. Lucifer was eventually accepted by NIST and was called DES or the Data Encryption Standard.
In 2000, NIST accepted Rijndael, and named it as AES or the Advanced Encryption Standard.
CiphersIn cryptography, a cipher is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment.
Answer: WELCOME
Stream cipher
A Stream Cipher is a secret-key encryption algorithm that encrypts a single bit at a time. With a Stream Cipher, the same plaintext bit or byte will encrypt to a different bit or byte every time it is encrypted.
e.g. :
Plain text: Pay 100
Binary of plain text: 010111101 (hypothetical)
Key: 100101011 ----- Perform XOR
____________________
Cipher text 110010110 ----- ZTU9^%D
To decrypt make the XOR operation of the cipher text with the key .
Block cipher
Block cipher technique involves encryption of one block of text at a time .Decryption also takes one block of encrypted text at a time. Length of the block is usually 64 or 128 bits.
e.g. :
Plain text: four and five
Four and five
Key Key Key
wvfa ast wvfa --- cipher text
Public Key Cryptosystem
Public key cryptography is a scheme that uses a Pair of keys for encryption: a Public key, which encrypts data, and a corresponding Private key (secret key) for decryption.
CRYPTOGRAPHY METHODS
Symmetric Same key for encryption and decryption
Key distribution problem
Asymmetric Key pairs for encryption and decryption
Public and private keys
Symmetric Algorithm
It is also called as Secret Key Cryptography Single key used for both encrypt & decrypt
Key must be known to both the parties
Encryption Decryption
Key
Plaintext Ciphertext
OriginalPlaintext
Symmetric Cryptosystem
Symmetric Algorithm
Data Encryption Standard (DES): 56 bits key
Advance Encryption Standard (AES):
128, 192 or 256 bits key
International Data Encryption Algorithm(IDEA):
128 bits key
Asymmetric Algorithm
Private keys are used for decrypting. Public keys are used for encrypting
encryptionplaintext ciphertext
public key
decryptionciphertext plaintext
private key
Hybrid cryptosystem
A hybrid cryptosystem can be constructed using any two separate cryptosystems:
a key encapsulation scheme, which is a public-key cryptosystem,
a data encapsulation scheme, which is a symmetric-key cryptosystem.
COMMON TYPES OF ATTACKS
Brute force Trying all key values in the keyspace.
Chosen Ciphertext Decrypt known ciphertext to discover key.
Dictionary Attack Find plaintext based on common words.
Frequency Analysis Guess values based on frequency of occurrence.
References
An introduction to cryptography and cryptanalysis
-Edward Schaefer,Santa Clara University
http://en.wikipedia.org/wiki/History_of_cryptography
https://securityblog.redhat.com/2013/08/14/a-brief-history-of-cryptography/
Contemporary Cryptography - Rolf Oppliger
Cryptography Theory And Practice - Douglas Stinson
Modern Cryptography Theory and Practice - Wenbo Mao
One must acknowledge with cryptography noamount of violence will ever solve a math problem
― Jacob Appelbaum, Cypherpunks: Freedom and the Future of the Internet