School of Computer Science & Information Technology
Presentation On
Elementary Cryptography
Presented by:
Anshul Jain (NM)
Sumit Lole (CS)
M.Tech. II sem
Guided by:
Dr. D.S. Bhilare
Agenda Introduction
Basic Terminologies Techniques of Cryptography Need of Cryptography Encryption Algorithm
Symmetric Asymmetric
Uses of Encryption Digital Signature
What is Elementary Cryptography? “Hidden Writing” Increasingly used to protect Information.
Goal of Cryptography Ensure security of communication over insecure
medium Privacy (secrecy, confidentiality) Integrity
Communicate even with possibility of adversaries
Introduction
Basic Terminologies
Encryption Encryption is the process of encoding a message
so that its meaning is not obvious Decryption
Decryption is the reverse process, transforming an encrypted message back into its normal, original form
Cryptosystem A system for encryption and decryption is called a
cryptosystem.
Cont… Plaintext Ciphertext Key –
key refers to a sequence of symbols or a numerical value used by an algorithm to alter information & making that information secure
Encryption algorithm The cryptosystem involves a set of rules for how to
encrypt the plaintext and how to decrypt the ciphertext. Cryptanalysis
Cryptanalysis is an attempt to break the ciphertext.
Substitution Technique Caesar Cipher Monoalphabetic Cipher Homophonic Cipher Polygram substitution cipher Polyalphabetic Cipher
Vigenère
Transposition Technique Rail Fence Technique. Vernam Cipher(One -time Pads)
Randomly generated Pad Running Key Cipher. Playfair Cipher. Hill Cipher.
Techniques of Cryptography
Cont… Stream-based Ciphers
One at a time, please Mixes plaintext with key stream Good for real-time services
Block Ciphers Amusement Park Ride Substitution and transposition
Confusion Ciphertext has no clue about Plaintext
Diffusion Spreading plain text across rows and columns
http://www.simonsingh.net/The_Black_Chamber
Need of Encryption
Confidentiality Integrity Authenticity Nonrepudiation Access Control
Encryption Algorithm
Symmetric Same key for encryption and decryption Key distribution problem
Asymmetric Mathematically related key pairs for encryption and
decryption Public and private keys
Hybrid Combines strengths of both methods Asymmetric distributes symmetric key
Also known as a session key Symmetric provides bulk encryption
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 CiphertextOriginalPlaintext
Symmetric Cryptosystem
Asymmetric Algorithm
Private keys are used for decrypting. Public keys are used for encrypting
encryptionplaintext ciphertext
public key
decryptionciphertext plaintext
private key
Cont… It is also called as public key cryptography
Encryption DecryptionPlaintext Ciphertext
OriginalPlaintext
Asymmetric Cryptosystem
Decryption Key Kd
Encryption Key Ke
Comparison
Secret Key (Symmetric) Public Key (Asymmetric)
Number of Key 1 2
Protection of Key Must be kept secret One key must be kept secret 7 other can be freely exposed
Best Uses Cryptographic workhorse; secrecy and integrity of data, single characters to blocks of data, messages, files
Key exchange, authentication
Key Distribution Must be out-of-band Public key can be used to distribute other keys
Speed Fast Slow; typically, 10,000 times slower than secret key
Symmetric Algorithm Data Encryption Standard (DES)
Double DES Triple DES
Advance Encryption Standard (AES) Blowfish IDEA
Data Encryption Standard The data encryption algorithm
developed by IBM was based on Lucifer, and it is known as the Data Encryption Standard
It is also known as Data Encryption Algorithm
The DES algorithm is a careful and complex combination of two fundamental building blocks of encryption: Substitution and Transposition
DES uses only standard arithmetic and logical operations on numbers up to 64 bits long
Cont… 1st 64 bit plain text is handed over to initial
permutation function. IP is performed over the plain text. IP produces two halves of the permuted blocks
left plain text (LPT) & right plain text (RPT). Now LPT & RPT goes 16 rounds of encryption
process, each with its own key. Now LPT & RPT are rejoined and FINAL
PERMUTATION (FP) is performed on the combined block.
The result is 64 bit cipher text.
Advance Encryption Standard Developed by NIST in January1997 Algorithm had several restriction:
unclassified publicly disclosed available royalty-free for use worldwide symmetric block cipher algorithms, for blocks of
128 bits usable with key sizes of 128, 192, and 256 bits
It was adopted by US government in December 2001
Cont…
AES primarily uses: Substitution Transposition Shift Exclusive OR Addition Each cycle consist of
four step Byte substitution Shift row Mix column Add sub key
Comparison between DES & AES
DES AES
Date 1976 1997
Block Size 64 bits 128 bits
Key Length 56 bits(effective length)128, 192, 256 ( possibly more) bits
Encryption Primitive
Substitution, permutation
Substitution, shift, bit mixing
Cryptographic Primitive
Open Open
Design Close Open
Selection Process
SecretSecret, but accepted open public comment
Asymmetric Algorithm
Rivest Shamir Adleman (RSA) Encryption Diffie-Hellman Elliptic Curve Cryptography (ECC)
RSA It is named after its three inventors Rivest
Shamir and Adleman This algorithm was introduced in 1978 and
to date remains secure. RSA has been the subject of extensive
cryptanalysis, and no serious flaws have yet been found.
The encryption algorithm is based on the underlying problem of factoring large numbers.
Cont…
The two keys used in RSA, d and e, are used for decryption and encryption
Keys are actually interchangeable: Either can be chosen as the public
Let encryption key e and the decryption key d. P = E(D(P)) = D(E(P)) Any plaintext block P is encrypted as Pe mod n. The decrypting key d is carefully chosen so that (Pe)d
mod n = P
Cont… Choose any two prime numbers p=17 & q=11 Calculate n = p x q n = 187 Calculate n’ = (p-1) x (q-1 ) n’ = 160 Select e as relative prime to n’ and less than
n’ e=7 Calculate d such that d x e = 1 mod n’ d =
23 Public {7,187} Private {23,187}
Diffie- Hellman It is a cryptographic protocol that allows
two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure communications channel. This key can then be used to encrypt subsequent communications using a symmetric key cipher.
Cont…
Uses of Encryption Cryptographic Hash Function Key Exchange Digital Signature Public Key Protocol Certificate
Cryptographic Hash Function Cryptography can be used to seal a file,
encasing it so that any change becomes apparent. One technique for providing the seal is to compute a cryptographic function, sometimes called a hash or checksum or message digest of the file.
Digital Signature
A digital signature is a protocol that produces the same effect as a real signature: It is a mark that only the sender can make, but other people can easily recognize as belonging to the sender. Just like a real signature, a digital signature is used to confirm agreement to a message.
Properties of Digital Signature
A digital signature must meet two primary conditions: It must be unforgeable. If person P signs message M
with signature S(P,M), it is impossible for anyone else to produce the pair [M, S(P,M)].
It must be authentic. If a person R receives the pair [M, S(P,M)] purportedly from P, R can check that the signature is really from P. Only P could have created this signature, and the signature is firmly attached to M.
It is not alterable. After being transmitted, M cannot be changed by S, R, or an interceptor.
It is not reusable. A previous message presented again will be instantly detected by R.
Thank You
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