Transcript Review of basic cryptographically algorithm

Review of basic cryptographically algorithm
Asymmetric encoding (Private and Public Keys), Hash Function, Digital
Signatures and Certification
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Cryptography
Encryption and decryption
History of cryptography
Conventional cryptography
Public key cryptography
Key
Digital signature
Hash function
Digital certificates
Summary
Resources
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cryptography is the science of using
mathematics to encrypt and decrypt data
strong/week
cryptographically algorithm – cipher
cryptanalysis - attackers
plaintext
ciphertext
encryption
plaintext
decryption
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steganography
substitute encryption
shift of letters
tables
Vigneres crypt
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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
ciphertext
encryption
plaintext
decryption
Key management:
 fast
 expensive key
 useful for not moving date
 secure the way of the key
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Asymmetric coding
Public key
Private key
chiphertext
plaintext
encryption
plaintext
decryption
Key management:
 Solves the problem of key distribution
Systems:
 Elgamal
(Tahela Elgamala)
 RSA
(Rivest, Shamir, Adleman)
 DSA
(Digital Signature Algorithm)
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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
recipient’s private key used
to decrypt session key
chipertext
session key used
to decrypt ciphertext
original
plaintext
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big numbers measured in bits
public and private keys are mathematically
related
larger keys - cryptographically secure for a
longer period of time
very difficult to derive the private key from
the public key
stored in encrypted form
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verify that the information is intact
authentication and data integrity
non-repudiation
purpose as a handwritten signature
Public key
Signing
Private key
Verifying
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A one-way hash function takes variablelength 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
Hash function
plaintext
Plaintext
+
signature
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certs
changing information about the correct key
is a form of credential
used to thwart attempts to substitute one
person’s key for another
A digital certificate consists of three things:
 public key
 certificate information
(“Identity” information about the user,
such as name, user ID, and so on.)
 one or more digital signatures
 certificate server
user ID
user ID
signature
signature
cerrtificate
signature
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Now you know what is Cryptography
Cryptography uses nowadays private or
public keys or both
Digital signature is like your personal
signature
Hash function creates something like a
fingerprint
Digital certificates is like your ID card in the
society
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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/