Introduction to Cryptography

1. CRYPTOGRAPHY
- CEASER CIPHER
- BY JULIUS CEASER
{100 B.C TO 44 B.C}
FUBSWRJUDSKB
(Convertion of the word Crypyography with ceaser cipher)
1

2. WHAT AND WHY ?
WHAT ?
CRYPT + GRAPHY = HIDDEN + WRITING.
{ i.e } ENCRYPTING & DECRYPTING THE MESSAGES.
WHY ?
AVOID INFORMATION BEING TRAPPED , INTERCEPTED , DIVERTED ,
MODIFIED & FABRICATIED BY INTRUDER.
2

3. CRYPTOGRAPHY PROCESS
SENDER RECEIVER
PLAIN TEXTPLAIN TEXT
ENCRYPT DECRYPT
CIPHER TEXT
3

4. CIPHER TEXT / CEASER CIPHER
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
Ci = E ( Pi ) = Pi + K
K is considered as 3 here
4

5. DISADVANTAGES OF CIPHER TEXT
The one who knows the value of K will be
easily able to identify the hidden value
inside the cipher text.
It is even more easy to know the K value
when 2 or more people share the same
system.
5

6. ENCRYPTION PRINCIPLES , TYPES AND PROCESS
PROCESS
TYPES
SYMMETRIC,
SHARED-KEY OR
CONVENTIONAL
ENCRYPTION
ASYMMETRIC,
TWO-KEY OR
PUBLIC KEY
ENCRYPTION
TRANSPOSITIO
N
PRINCIPLE
S
SUBSTITUTIO
N
STREAM
CIPHER
BLOCK CIPHER
6

7. CRYPT - ANALYSIS
SCIENCE OF RECOVERING PLAIN-TEXT OF THE MESSAGE WITHOUT HAVING ACCESS TO THE KEY
ATTEMPTING TO DISCOVER PLAIN TEXT OR KEY OR BOTH
IT IS A ART OF BREAKING CIPHERS
CRYPT – ANALYSIS HAVE COMPLETE KNOWLEDGE OF ALGORITHM AND ITS IMPLEMENTATION
ALL SECURITY SHOULD RESIDE IN THE KEY AND NOT IN THE SECRECY OF ALGORITHM
7

8. TYPES OF CRYPTO – ANALYSIS ATTACKS
CIPHER TEXT ONLY ATTACK
KNOWN PLAIN TEXT ATTACK
CHOSEN PLAIN TEXT ATTACK
CHOSEN CIPHER TEXT ATTACK
CHOSEN KEY ATTACK
8
FORMULA :
Ci = EK (Pi )
&
Pi = DK ( Ci )

9. CHIPER TEXT ONLY ATTACK
IT IS ALSO KNOWN AS KNOWN CIPHER TEXT
ATTACKER CAN HAVE ACCESS TO ONLY A SET OF CIPHER TEXT , KNOWLEDGE ON
WITH PLAIN TEXT & CAN BE GUESSED EASILY
THEY CANNOT HAVE ACCESS TO ANY CHANNEL PROVIDING ACCESS PRIOR TO
ENCRYPTION
IT IS ALMOST SUCCESSFUL
SYNTAX :
C1 = EK ( P1 ), C2 = EK ( P2 ), …… Ci = EK ( Pi ).
9

10. KNOWN PLAIN TEXT ATTACK
THE ATTACKER HAS ACCESS TO BOTH PLAIN TEXT AND CIPHER TEXT.
CIPHER TEXT & PLAIN TEXT OF THE CORRESPONSDING MESSAGES ARE
PAIRED UP TOGETHER WITH SECRET KEY.
THEY ARE COMPARED TO REVEAL FURTHER SECRET INFORMATION SUCH AS
SECRET KEY AND CODE.
SYNTAX :
P1 , C1 = EK ( P1 ) , P2 , C2 = EK ( P2 ) , ……. P1 , Ci = EK ( Pi ).
10

11. CHOSEN PLAIN TEXT ATTACK
THE ATTACKER CAN ENCRYPT PLAIN TEXT MESSAGES
COMPARE CIPHER TEXT WITH THE RESULT OF ANOTHER ENCRYPTION TO
POSSIBLY DISCOVER THE KEY BY MATCHING THE TWO
IT IS FEASIBLE.
SYNTAX :
P1 , C1 = EK ( P1 ) , P2 , C2 = EK ( P2 ) , ………. Pi , Ci = EK ( Pi ).
11

12. CHOSEN CIPHER TEXT ATTACK
CAN CHOOSE DIFFERENT CIPHER TEXTS TO BE DECRYPTED WHICH
IS DONE IN VICTIM’S SYSTEM.
ACCESS TO DECRYPTED PLAIN TEXT
SYNTAX :
C1 , P1 = DK ( C1 ) , C2 , P2 = DK ( C2 ) , ….. Ci , Pi = DK ( Ci ).
12

13. CHOSEN TEXT ATTACK
THE ATTACKER CAN ENCRYPT PLAIN TEXT MESSAGES
COMPARE CIPHER TEXT WITH THE RESULT OF ANOTHER
ENCRYPTION AND ALSO COMPARED WITH DECRYPTED PLAIN
TEXT TO POSSIBLY DISCOVER THE KEY BY MATCHING THE TWO.
13

14. CONVENTIONAL ENCRYPTION MODEL
PLAIN
TEXT
INPUT
ENCRYPTION
ALGORITHM
DECRYPTION
ALGORITHM
PLAIN
TEXT
OUPUT
TRANSMITTE
D
CIPHER
TEXT
SHARED KEY
BY
SENDER & RECEIVER
SHARED KEY
BY
SENDER & RECEIVER
14

15. STEPSANDPROBLEMINTHIS
MODEL
STEPS :
• CONVERT P -> C BY K
C = EK ( P )
• CONVERT C -> P BY USING SAME
K
P = DK ( C )
=> IMPLIES : P = DK ( EK ( P ) )
SECRECY OF ENCRPTION
DEPENDENTS ON SECRECY OF KEY &
NOT ON SECRECY OF ALGORITHM.
PROBLEMS :
 LARGE NUMBER OF PEOPLE
CANNOT USE IT
 THERE IS NO SCOPE FOR QUALITY
CONTROL OR
STANDARDIZATION.
 NO GUARANTEE FOR EFFECTIVE 15

16. PUBLIC KEY CRYPTO-SYSTEMS
PLAIN
TEXT
INPUT
ENCRYPTION
ALGORITHM
DECRYPTION
ALGORITHM
PLAIN
TEXT
OUPUT
TRANSMITTE
D
CIPHER
TEXT
ENCRPTION KEY USED BY
SENDER
DECRYPTION KEY USED
BY RECEIVER
16

17. STEPS AND PROBLEM IN THIS MODEL
STEPS :
• CONVERT P -> C BY K1
C = EK1 ( P )
• CONVERT C -> P BY USING K2
P = DK2 ( C )
=> IMPLIES : P = DK2 ( EK1 ( P ) )
PROBLEMS :
 THEY ARE SLOWER.
 IT IS NOT SURE THAT THE DECRYPTED
IS ACTUAL TEXT FORWARDED BY THE
SENDER
17

18. APPLICATIONS OF CRYPTOGRAPHY
SECURE COMMUNICATIONS :
WEB ENCRYPTION
HTTP TO HTTPS
END–TO-ENCRYPTION :
EMAIL
STORING DATA :
HASH PROGRAMS
18

19. CRYPTOGRAPHY TECHNOLOGY
• DIGITAL SIGNATURE :
ASSURE THAT :
SIGNATORY HAS SIGNED THE INFORMATION &
INFORMATION IS NOT MODIFIED
STANDARDS USED :
FEDERAL INFORMATION PROCESSING STANDARD
DIGITAL SIGNATURE STANDARDS
USED ALGORITHMS TO GENERATE AND VERIFY :
DSA
RSA
ECDSA
WITH RESPECT TO APPROVED HASH FUNCTIONS SPECIFIED IN FIPS 180-4 , SECURE HASH FUNCTIONS OR FIPS 202
,
SHA-3 STANDARD : PERMUTATION- BASED HASH AND EXTENDABLE – OUTPUT FUNCTIONS.
TESTING DSS IMPLEMENTATIONS USING CAVP ( CRYPTOGRAPHIC ALGORITHMS VALIDATION PROGRAM )
19

20. AVAILED CRYPTOGRAPHIC ALGORITHMS
CONVENTIONAL ALGORITHMS :
DES - DATA ENCRPTION STANDARD
IDEA – INTERNATIONAL DATA
ENCRYPTION ALGORITHM
AES – ADVANCED ENCRYPTION
STANDARD
SOME OTHERS :
SMS4 , ADFGVX , BACON ,
STRADDLING CHECKBOARD , BLOW
FISH , AUTOKEY , RABBIT , TRIFID ,
ETC.
PUBLIC KEY ALGORITHMS :
RSA
MD5 – MESSAGE DIRECT ALGORITHM
SHA – SECURED HASH ALGORITHM
SOME OTHERS :
CRAMER – SHOUP CRYPTOSYSTEM ,
YAK , PAILLIER CRYPTOSYSTEMS ,
ELGAMAL , DSS , DIFFIE – HELLMAN
KEY EXCHANGE , NTRUENCRYPT ,
MCELIECE ENCYPTOSYSTEMS , ETC.
20

21. THANKYOU