Review of basic cryptographically algorithm

Asymmetric encoding (Private and Public Keys), Hash Function, Digital Signatures and Certification

Cryptography Encryption and decryption History of cryptography Conventional cryptography Public key cryptography Key Digital signature Hash function Digital certificates Summary Resources

cryptography is the science of using mathematics to encrypt and decrypt data

strong/weekcryptographically algorithm – ciphercryptanalysis - attackers

plaintext

encryption decryption

ciphertext plaintext

steganographysubstitute encryptionshift of letters tablesVigneres crypt

T H I S I S T H E M E S S A G E

K E Y K E Y K E Y K E Y K E Y K

A T Y E Y E A T H P H E E Q K H

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secret-key or symmetric-key encryption Data Encryption Standard DAS

plaintext

encryption decryption

ciphertext plaintext

Key management: fastexpensive keyuseful for not moving datesecure the way of the key

Asymmetric coding

plaintext

encryption decryption

chiphertext plaintext

Public key Private key

Key management:Solves the problem of key

distributionSystems:Elgamal (Tahela Elgamala)RSA (Rivest, Shamir, Adleman) DSA (Digital Signature

Algorithm)

PGP - private and public key cryptography

compresses the plaintext program used for sending E-mails

plaintext is encrypted with a session key

session key is encrypted with public key

cipher text and encrypted

session key

encrypted message

encrypted session key

chipertext

recipient’s private key usedto decrypt session key

session key usedto decrypt ciphertext

originalplainte

xt

big numbers measured in bitspublic and private keys are

mathematically related larger keys - cryptographically

secure for a longer period of timevery difficult to derive the private

key from the public keystored in encrypted form

verify that the information is intactauthentication and data integritynon-repudiationpurpose as a handwritten signature

Signing Verifying

Public key Private key

A one-way hash function takes variable-length message of any length

Produces a fixed-length output (160-bits)

Ensures that, if the information is changed an entirely different output value is produced

plaintext

Plaintext+

signature

Hash function

certschanging information about the

correct key is a form of credentialused to thwart attempts to

substitute one person’s key for another

A digital certificate consists of three things:

public keycertificate information

(“Identity” information about the user, such as name, user ID, and so on.)

one or more digital signaturescertificate server

cert

ifica

tio

n

user ID

cerrtificate

user ID

signature

signature

signature

Now you know what is CryptographyCryptography uses nowadays private

or public keys or both Digital signature is like your personal

signatureHash function creates something like

a fingerprintDigital certificates is like your ID

card in the society

http://cs.wikipedia.org/wiki/Kryptografie http://fisher.osu.edu/~muhanna_1/pdf/crypto.pdf http://axion.physics.ubc.ca/crypt.html http://www.austinlinks.com/Crypto/