CONVENTIONAL ENCRYPTION

CONVENTIONAL ENCRYPTION

1. CONVENTIONAL
ENCRYPTION
Prof. NeerajBhargava
Mrs. Shubha Chaturvedi
Department of Computer Science, School of Engineering & System Sciences
MDS University Ajmer, Rajasthan

2. INTRODUCTION TOCONVENTIONAL
ENCRYPTION
CONVENTIONALENCRYPTIONARECRYPTOGRAPHIC
SYSTEMWHICHUSESSAMEKEYUSEDBYSENDERTO
ENCRYPTMESSAGEANDBYRECEIVERTODECRYPT
MESSAGE.ITWASONLYTYPEOFENCRYPTIONINUSE
PRIORTODEVELOPMENTOFPUBLIC-KEYENCRYPTION.
ITISSTILLMUCHPREFERREDOFTHETWOTYPESOF
ENCRYPTIONSYSTEMSDUETOITSSIMPLICITY.ITISA
RELATIVELYFASTPROCESSSINCEITUSESASINGLEKEY
FORBOTHENCRYPTIONANDDECRYPTIONINTHIS
ENCRYPTIONMODEL,THESENDERENCRYPTSPLAINTEXT
USINGRECEIVER’SSECRETKEY,WHICHCANBELATER
USEDBYRECEIVERTODECRYPTCIPHERTEXT.

3. BELOWISFIGURETHAT
ILLUSTRATETHISCONCEPT.

4. EXPLANATION :
SUPPOSEAWANTSTOSENDAMESSAGETOB,THATMESSAGEISCALLED
PLAINTEXT.NOW,TOAVOIDHACKERSTOREADPLAINTEXT,PLAINTEXTIS
ENCRYPTEDUSINGALGORITHMANDASECRETKEY(AT1).THIS
ENCRYPTEDPLAINTEXTISCALLEDCIPHERTEXT.USINGSAMESECRETKEY
ANDENCRYPTIONALGORITHMRUNINREVERSE(AT2),BCANGET
PLAINTEXTOFAANDTHUSMESSAGEISREADANDSECURITYIS
MAINTAINED.
THEIDEATHATUSESINTHISTECHNIQUEISVERYOLDANDTHAT’SWHY
THISMODEL ISCALLED CONVENTIONAL ENCRYPTION

5. A CONVENTIONALENCRYPTIONHASMAINLY5 INGREDIENTS
•Plaintext–thusmessageisreadandsecurityismaintained.
•Encryptionalgorithm–Encryptionalgorithmperformsvarious
transformationsonplaintexttoconvertitintociphertext.
•Secretkey–Secretkeyisalsoaninputtothealgorithm.The
encryptionalgorithmwillproducedifferentoutputbasedon
thekeysusedatthattime.
•Ciphertext–Itcontainsencryptedinformationbecauseit
containsaformoforiginalplaintextthatisunreadablebya
humanorcomputerwithoutproperciphertodecryptit.Itis
outputfromalgorithm.
•Decryptionalgorithm–Thisisusedtorunencryption
algorithminreverse.CiphertextandSecretkeyisinputhere
anditproducesplaintextasoutput.

6. ADVANTAGESOFCONVENTIONALENCRYPTION
1.Simple :
This type of encryption is easy to carry out.
2.Useslesscomputerresources:
Conventionalencryptiondoesnotrequirealotofcomputer
resourceswhencomparedtopublickeyencryption.
3.Fast:
Conventionalencryptionismuchfasterthanasymmetric
keyencryption.

7. DISADVANTAGESOFCONVENTIONALENCRYPTION
1.Originandauthenticityofmessagecannotbeguaranteed,
sincebothsenderandreceiverusethesamekey,messages
cannotbeverifiedtohavecomefromaparticularuser.
2.Itisn’tmuchsecuredwhencomparedtopublickey
encryption.Ifthereceiverlostthekey,he/shecantdecrypt
theandthusthewhole
3.Thisschemedoesnotscalewelltoalargenumberofusers
becauseboththesenderandthereceivertoagreeonasecret
keybeforetransmission.

8. SYMMETRICENCRYPTION:

9. SYMMETRICENCRYPTIONISAFORMOFCRYPTOSYSTEMINWHICH
ENCRYPTIONANDDECRYPTIONAREPERFORMEDUSINGTHESAMEKEY. ITIS
ALSOKNOWNASCONVENTIONALENCRYPTION.
Two requirements for secure use of symmetric encryption:
–A strong encryption algorithm
–A secret key known only to sender / receiver
Y = EK(X)
X = DK(Y)
.assume encryption algorithm is known
.implies a secure channel to distribute key

10. Asourceproducesamessageinplaintext,X=[X1,X2…XM]whereMarethe
numberoflettersinthemessage.AkeyoftheformK=[K1,K2…KJ]isgenerated.If
thekeyisgeneratedatthesource,thenitmustbeprovidedtothedestinationby
meansofsomesecurechannel.
WiththemessageXandtheencryptionkeyKasinput,theencryptionalgorithm
formstheciphertextY=[Y1,Y2,YN].Thiscanbeexpressedas
Y = EK(X)
Theintendedreceiver,inpossessionofthekey,isabletoinvert
thetransformation:
X = DK(Y)
Anopponent,observingYbutnothavingaccesstoKorX,mayattempttorecoverX
orKorboth.Itisassumedthattheopponentknowstheencryptionanddecryption
algorithmsIftheopponentisinterestedinonlythisparticularmessage,thenthe
focusofeffortistorecoverbygeneratingaplaintextestimate.Ofteniftheopponent
isinterestedinbeingabletoreadfuturemessagesaswell,inwhichcaseanattempt
ismadetorecoverKbygeneratinganestimate.

11. ASSIGNMENT
Q1. Explain the Conventional Encryption model in Detail?