cryptography gayathri v.r. kunapuli. outline history of cryptography need for cryptography private...
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CRYPTOGRAPHYCRYPTOGRAPHY
Gayathri V.R. Kunapuli
OUTLINEOUTLINEHistory of CryptographyNeed for cryptographyPrivate Key CryptosystemsPublic Key CryptosystemsComparison between Public and
Private Key CryptosystemsPEMFuture Work
History of History of Cryptography[2]Cryptography[2]Ceaser CiphersTransposition CipherSubstitution CipherVigene`re CipherEnigma Machine
Need for Cryptography[1]Need for Cryptography[1]Authentication of the
Communicating PrincipalsAuthenticated message carries a
Digital Signature
Private Key Private Key Cryptosystems[1,2]Cryptosystems[1,2]Also called Symmetric
CryptographyEncryption algorithm E turns plain
text message M into a cipher text CC=E(M)Decrypt C by using decryption
algorithm D which is an inverse function of E
M=D(C)
Private Key Cryptosystems Private Key Cryptosystems cont[1,2]cont[1,2]Algorithm decomposed into
Function(public) and Key(secret)Encrypted using the key Ke and
decrypted using the key KdM=DKd(EKe(M))
• A function and a variable number of keys constitute a class of algorithms indexed by the keys.
Cont…Cont…The encryption function is
-One-to-one injective mapping
-One way function • The secrecy rests on the keys
rather than on algorithms. • The key should be of sufficient
length in bits.
DES(Jan,1977)[1,2]DES(Jan,1977)[1,2]Encryption consists of 3 stages of
Transposition and 16 stages of Substitution of bits.
Easy to implement on VLSIThe 56-bit length key was found
insufficient and easy to breakRepetitions in cipher text give
clues to eavesdroppersSpurious data can be injected
Contd…Contd…Private Key systems require
[n*(n-1)]/2 keys for ‘n’ principals in a system
The conversation key must be agreed upon beforehand
Management of the keys is a function of the Key Distribution Server(KDS)
Public Key Cryptographic Public Key Cryptographic SystemsSystems(Need)[1](Need)[1]Also called as the Asymmetric
CryptographyTo avoid the need to transmit
secret keys andTo reduce the key requirement to
2n, the public key systems are used
Public Key Cryptosystems Public Key Cryptosystems ContContIntroduced by Diffie and HellmanEach principal keeps a set of encryption
keys (Ke & Kd)Encryption algorithm E is public and so is
the key KeDecryption algorithm D and decryption
key Kd is kept privateData sent to a principal is encrypted using
that corresponding KeE and D can be made public if Ke and Kd
are chosen such that it is impossible to infer Kd from Ke.
RSA(Aug,1977)[1,2,5]RSA(Aug,1977)[1,2,5]The algorithms E and D are inversesPlain text messages are limited to a
size is limited to ‘k’Integer k is chosen such that 2k < NN =p * q where p & q are LARGE
prime numbersKp (public encyrption key) and Ks
(private decryption key) are derived from p & q
ContdContdThe robustness of RSA algorithm
relies on the computational complexity in factoring a large number upon which the keys are based.
The authenticity of the sender can also be verified.
Comparison between the Comparison between the cryptosystems[1]cryptosystems[1]Private Key DES is
computationally efficientPublic Key RSA is
computationally expensivePossible best use is RSA for
short/important data and DES for long or less critical
PEM[1,5]PEM[1,5]Provides mechanism for the mail
users to specify the cryptographic algorithm and parameters to be used for mail messages.
Essential data fields in PEM are◦DEK◦IK◦MIC
Extended Works[4]Extended Works[4]To prevent the Denial-of-
Decryption To reduce the time taken for the
authentication of the digital signatures
Self Generated Certificate Public Key Cryptography
ReferencesReferences1. Chow, Randy; Johnson, Theodore;
Distributed Operating Systems & Algorithms, 19982. Aiden A.Bruen,Mario A.Forcinito; Cryptography,
Information theory and Error-correction,20053.www.wikipedia.org/history of cryptography4. Self generated certificate public key
cryptography and certificateless signature/Encryption scheme in the standard model
ASIACCS’07, March 20-22, 2007, Singapore.5.http://www.cybercrimes.net/
Cryptography/Articles/Hebert.html (April 2007)
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