A Comparison Between ‘Encryption and Decryption’

7/24/2019 A Comparison Between Encryption and Decryption

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A Comparison Between Encryption

And Decryption AlgorithmsSubmitted by

Name: R!" #A$$NA"%

Regd& No& '()'*'(*'*

Department o+ Computer Science , Engineering

"$ER- SA .N"/ERS"$0- B1.BANES2AR


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$ypes o+ Cryptography

In private key cryptography or symmetric

key crytography , only one key is used for

encryption and decryption which is

shared among sender and receiver.

In public key cryptography or asymmetric

key , a user has a pair of cryptographic

keysa public key and a private key. The

private key is kept secret, while the public

key may be widely distributed.


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R.S.A

by Rivest, Shamir !dleman of "IT in #$%%RSAis an algorithm used by modern computers

to encrypt and decrypt messages.It is an

asymmetric cryptographic algorithm.

It is based on the fact that finding the factors ofa integer is hardand e&ponentiation in a finitefield over integers modulo a prime .


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RSA AlgorithmThe keys for the RS! algorithm are generated the

following way'#. (hoose two different large random prime numbers

pand q

). (alculate n=p*q

nis the modulus for the public key and the private

keys

*. (alculate the totient' (n) = (p 1)(q 1)

+. (hoose an integer esuch that 1 < e < (n), and

eis coprime to (n) ie: and share no factors

other than # gcd(e, (n) ) = 1.eis released as the public key e&ponent

-. (ompute to satisfy the congruence relation

de 1 mod((n))ie:d 1+k(n) for some

integer k. d is kept as the private key e&ponent.


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Encrypting !essages

!lice gives her public key n e/ to 0ob andkeeps her private key secret. 0ob wants to send

message !to !lice.1irst he turns !into a number smaller than n

by using an agreed2upon reversible protocol

known as a padding scheme. 3e then computes

the cipherte&t ccorresponding to' c=(m^e)

mod nThis can be done 4uickly using the method

of e&ponentiation by s4uaring. 0ob then sends c

to !lice.


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Decrypting !essages!lice can recover mfrom cby using her

private key e&ponent dvia computingm= (c^d) mod n

5iven m, she can recover the original

message M by reversing the padding

scheme

67T8' 0oth of the calculations inencryption and decryption can be

computed efficiently using the s4uare2and2

multiply algorithm for modular

e&ponentiation.


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A 2or3ing E4ample

3ere is an e&ample of RS! encryption and decryption.

#.(hoose two random prime numbers 'p=61 q=53).(ompute n=pq ; 61*53=3233

*.(ompute the totient (n) = (p 1)(q 1);60*52=3120

+.(hoose e>1coprime to 3120 ie e=1.

-.(hoose d to satisfy de 1 mod((n)); d=253ie

1*253= !6"01 =1+ 15*3120 The public key isn=3233,e=1/.1or a padded message

m,the encryption fuction is c=(m^e)mod n 9 (m^1)mod

3233 The private key isn=3233,d=253/.The decryption

function is m=(c^d)mod n= (c^253)mod 3233. for e&ample' to encrypt m=123,we calculate c=(123^1)

mod 3233="55

to decrypt c ="55, we calculate

m=("55^253)mod 3233=123


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DES5Data Encryption Standard6

It is a symmertic key algorithm i.e. one key is usedTo accomplish encryption, it uses two main techni4ues

known as substitution and permutation.Substitution is mapping of one value to another

whereas permutation is a reordering of the bit positionsfor each of the inputs.:sed a number of times in iterations called rounds.! non2linearity is also introduced into the encryption

so that decryption will be computationally infeasible

without the secret key. by S2bo&es/The only issue is the shared key with may be

breached by intruders.


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2or3ing o+ DES AlgorithmThe se4uence of events that occur during an encryption

operation.''& Initial permutation on the entire ;+ bit block of data. It

is then split into two *) bit sub2blocks,


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Input=64-bit PlainText

and Secretkey.i= e!t PartRi=Ri"ht Part#i=Subkey #$%6&4'-

bit(!= )ei*tel bl+ckcipher,utput=64-bitipher

Text


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Comparing DES and RSA

In the table ne&t, a comparative study between @8S andRS! is presented in to fourteen factors, which areAey SiBe,0lock SiBe,(iphering @eciphering key,

!lgorithm,8ncryption,@ecryption,Cower (onsumption,Security,

Inherent Dulnerabilities,Aey used,Rounds,Stimulation Speed,3ardware Software Implementation and

(iphering @eciphering !lgorithm.


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9AC$RS DES RSA

e/el+ped in year 1977 1978

#ey Si0e 56 bits >1024 bits

1l+ck Si0e 64 bits Minimum 512 bits

ipherin" 2decipherin" key

Same Diferent

Al"+rith3 Symmetric A!"rit#m Asymmetric A!"rit#m

ncrypti+n M"derate S"$er

ecrypti+n M"derate S"$erP+wer +n*u3pti+n %"$ &i!#

Security '"t Secure (n"u!# %east Secure

Inherent5ulnerabilitie*

)rute *"rced+ %inear anddiferentia cry,tanaysis

attac-

)rute *"rced and race

#ey *ed Same -ey used Diferent -ey used

R+und* 16/Siteen 1/"ne

7ardware 2 S+!twareI3ple3entati+n

)etter in #ard$are t#anin s"t$are

'"t (3cient

ipherin" 2eci herin

Diferent Same


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Conclusion8ncryption algorithm plays very important role in

communication security. The presentation surveyed the performance of

e&isting encryption techni4ues like @8S and RS!

algorithms.0ased on the te&t files used and the e&perimental

result it was concluded that RS! consumes longestencryption time.Ee also observed that @ecryption of d8S algorithm is

better than RS!algorithm.1rom the simulation result, we evaluated that @8S

algorithm is much better than RS! .7ur future work will focus on compared and analysed

e&isting cryptographic algorithm like !8S, @8S and

RS!. It will include e&periments on image and audio

data and focus will be to improve encryption time and

decryption time.


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Re+erences

http'[email protected]'FFglobalHournals.orgF5(STJDolume#*F+2!2Stud

y2of28ncryption2!lgorithms.pdf

http'FFwww.cryptographyworld.comFdes.htmlhttps'FFsimple.wikipedia.orgFwikiFRSAJalgorithm/

https'FFen.wikipedia.orgFwikiF@ataJ8ncryptionJStand

ard

https'FFimages.google.com
http://www.facweb.iitkgp.ernet.in/~sourav/DES.pdfhttps://globaljournals.org/GJCST_Volume13/4-A-Study-of-Encryption-Algorithms.pdfhttps://globaljournals.org/GJCST_Volume13/4-A-Study-of-Encryption-Algorithms.pdfhttp://www.cryptographyworld.com/des.htmlhttps://simple.wikipedia.org/wiki/RSA_(algorithm)https://simple.wikipedia.org/wiki/RSA_(algorithm)https://simple.wikipedia.org/wiki/RSA_(algorithm)https://simple.wikipedia.org/wiki/RSA_(algorithm)https://simple.wikipedia.org/wiki/RSA_(algorithm)https://en.wikipedia.org/wiki/Data_Encryption_Standardhttps://en.wikipedia.org/wiki/Data_Encryption_Standardhttps://images.google.com/https://images.google.com/https://en.wikipedia.org/wiki/Data_Encryption_Standardhttps://en.wikipedia.org/wiki/Data_Encryption_Standardhttps://simple.wikipedia.org/wiki/RSA_(algorithm)https://simple.wikipedia.org/wiki/RSA_(algorithm)https://simple.wikipedia.org/wiki/RSA_(algorithm)https://simple.wikipedia.org/wiki/RSA_(algorithm)https://simple.wikipedia.org/wiki/RSA_(algorithm)http://www.cryptographyworld.com/des.htmlhttps://globaljournals.org/GJCST_Volume13/4-A-Study-of-Encryption-Algorithms.pdfhttps://globaljournals.org/GJCST_Volume13/4-A-Study-of-Encryption-Algorithms.pdfhttp://www.facweb.iitkgp.ernet.in/~sourav/DES.pdf


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A Comparison Between ‘Encryption and Decryption’