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Cryptography. The science of writing in secret code. Cryptography is an ancient art - first documented use of cryptography in writing dates back to circa 1900 B.C. when an Egyptian scribe used non-standard hieroglyphs in an inscription - PowerPoint PPT Presentation
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Cryptography The science of writing in secret
code
The Science of Writing In Secret Code
• Cryptography is an ancient art - first documented use of cryptography in writing dates back to circa 1900 B.C. when
an Egyptian scribe used non-standard hieroglyphs in an inscription
• New forms of cryptography came soon after the widespread development of computer communications
Secure Communication• Crypto is the secure communication in the
presence of third parties (adversaries)• Generally: about constructing and analyzing
protocols that overcome such adversaries
• MAIN GOAL: SECURITY!
DISCIPLINES• Modern crypto intersects disciples of Math,
Computer Science, and Electrical Engineering
• APPLICATIONS: ATM cards, computer passwords, electronic commerce, etc.
Related to various aspects in information security such as data confidentiality, data integrity, authentication
Specific Security Requirements
• Authentication: process of proving one’s identity
• Privacy/confidentiality: ensuring that no one can read the message except the intended receiver
• Integrity: assuring the intended receiver that the original message has not been altered in any way
• Non-repudiation: mechanism to prove that sender really sent the message
Cryptographic Schemes
• Initial unencrypted date is referred to as plaintext• It is then encrypted into ciphertext• Then decrypted into usable plaintext
PLAINTEXT CIPHERTEXT PLAINTEXT
Types of Cryptography
• Secret Key Cryptography (SKC)• Public Key Cryptography (PKC)
•Hash Functions
Crypto
SECRET KEY ENCRYPTIONAlso known as private key & symmetric key
Secret Key Encryption
Public Key Encryption
Why Three?
• Each scheme is optimized for some specific applications
• Secret Key Cryptography is suited for encrypting messages as it provides privacy and
confidentiality• Public Key Cryptography is ideal for non-
repudiation and user authentication• Hash functions ensure data integrity
Caesar Cipher
Roman ruler Julius Caesar used a very simple cipher for secret communicationInvolves the use of a “displacement” concept
Caesar cipher is the simplest to solve, since there are only 25 possible combinations
Caesar Cipher
Outside wheel: The Alphabet
Inner wheel: can be rotated so that any letter on one wheel can be aligned with any letter on the other wheel - The inner wheel becomes the key
A lock is only as strong as its weakest link
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