TOTURIAL CRYPTOGRAPHY Ver :1. Things to learn about Concepts of encryption Cryptanalysis Symmetric encryption Asymmetric encryption Protocols.

TOTURIAL TOTURIAL CRYPTOGRAPHYCRYPTOGRAPHY

Ver :1Ver :1

Things to learn aboutThings to learn about

Concepts of encryptionConcepts of encryption CryptanalysisCryptanalysis Symmetric encryptionSymmetric encryption Asymmetric encryptionAsymmetric encryption Protocols and certificatesProtocols and certificates Digital signaturesDigital signatures Types of encryption algorithmsTypes of encryption algorithms

Map EncryptionMap Encryption

Basic Concept Encryption

Substitution(Penggantian)

Transposition(Peralihan)

Monoalphabetic Polyalphabetic Columnar Algorithm Transposition

Double Transposition Algo

Stream dan Block Ciphers

Good Ciphers nature

Shannon Characteristics

Concept Confusion and Diffusion

Testing information Theory

Caesar Cipher

Use of key

Vigenere Tableux

One Time Pad(Vernam Cipher)

Technic for criptanalisys

Kasiski method

Index of Coefficient

CryptographyCryptography

Secret writing – strongest tool to control Secret writing – strongest tool to control against many kinds of security threatsagainst many kinds of security threats

Users of cryptography usually do not Users of cryptography usually do not create their encryption techniques – just create their encryption techniques – just use what’s availableuse what’s available

TerminologyTerminology

Imagine S (sender) sending a message to R Imagine S (sender) sending a message to R (recipient) through T (transmission medium)(recipient) through T (transmission medium)

However there’s an intruder or interceptor (O) However there’s an intruder or interceptor (O) who tries to access the message in any of these:who tries to access the message in any of these: Block it – affects the availabilityBlock it – affects the availability Intercept it – affecting the confidentialityIntercept it – affecting the confidentiality Modify it – affecting the integrityModify it – affecting the integrity Fabricate it – affecting the integrity as wellFabricate it – affecting the integrity as well

Cryptography EvolutionCryptography Evolution 500 BC-Pendita Hebrew introduce the 500 BC-Pendita Hebrew introduce the

Cryptography CodeCryptography Code 1863 -Cipher Cryptanalisys Kasiski are 1863 -Cipher Cryptanalisys Kasiski are

introducedintroduced 1883-Sistem Enkripsi Kerchoff 1883-Sistem Enkripsi Kerchoff 1917-One-time pad by Gilbert Vernam (AT&T). 1917-One-time pad by Gilbert Vernam (AT&T). 1917-Father of field the cryptanalysis US, 1917-Father of field the cryptanalysis US,

William Friedman, Herbert Yardley. William Friedman, Herbert Yardley. 1919-Rotor machine are create by Koch and 1919-Rotor machine are create by Koch and

Damm.Damm.

……continuedcontinued

Encryption – the process of encoding a Encryption – the process of encoding a message (scrambling)message (scrambling)

Decryption – the process to reverse, Decryption – the process to reverse, transforming encrypted message back to original transforming encrypted message back to original formform

Encode, decode, encipher, decipher are terms Encode, decode, encipher, decipher are terms used in lieu of encrypt or decryptused in lieu of encrypt or decrypt

Encode could mean translating entire word or Encode could mean translating entire word or phrases into something newphrases into something new

Encipher could mean translating letters or Encipher could mean translating letters or symbols individuallysymbols individually


Cryptosystem – a system for encryption Cryptosystem – a system for encryption and decryptionand decryption

Plaintext, cleartext – original formPlaintext, cleartext – original form Ciphertext – encrypted (scrambled) formCiphertext – encrypted (scrambled) form

Encryption DecryptionPlaintext Ciphertext OriginalPlaintext

Encryption AlgorithmsEncryption Algorithms

Set of rules for how to encrypt plaintext Set of rules for how to encrypt plaintext and how to decrypt ciphertextand how to decrypt ciphertext

Often use a device called ‘key’ (K)Often use a device called ‘key’ (K) When C=E(K,P), it means E acts as an When C=E(K,P), it means E acts as an

encryption algorithm, and K is the key. C encryption algorithm, and K is the key. C is ciphertext; P is plaintextis ciphertext; P is plaintext


When P=D(K, E(K,P)), it shows that both When P=D(K, E(K,P)), it shows that both encryption and decryption keys are the encryption and decryption keys are the samesame This form is called ‘symmetric’ encryptionThis form is called ‘symmetric’ encryption

When P=D(KWhen P=D(KDD, E(K, E(KEE,P)), it shows that ,P)), it shows that encryption and decryption keys are NOT encryption and decryption keys are NOT the samethe same This form is called ‘asymmetric’ encryptionThis form is called ‘asymmetric’ encryption



KEY


KKEE KKDD

Encryption Key Decryption Key

SYMMETRIC ENCRYPTION

ASYMMETRIC ENCRYPTION


A key gives flexibility in using an A key gives flexibility in using an encryption schemeencryption scheme

Can create different encryptions by just Can create different encryptions by just changing the keychanging the key

Provides additional securityProvides additional security Any encryption scheme that does not Any encryption scheme that does not

require a key = keyless cipherrequire a key = keyless cipher

Some interesting terms…Some interesting terms…

Cryptography – hidden writing, practice of Cryptography – hidden writing, practice of using encryption to conceal textusing encryption to conceal text

Cryptanalyst – studies encryption and Cryptanalyst – studies encryption and encrypted messages, hoping to find encrypted messages, hoping to find hidden messageshidden messages

Cryptographer (& cryptanalyst) attempt to Cryptographer (& cryptanalyst) attempt to translate coded material to plaintexttranslate coded material to plaintext


Cryptographer works on behalf of a Cryptographer works on behalf of a legitimate sender/receiverlegitimate sender/receiver

Cryptanalyst works on behalf of an Cryptanalyst works on behalf of an unauthorized interceptorunauthorized interceptor

Cryptology – research into and study of Cryptology – research into and study of encryption and decryptionencryption and decryption

Two simples typesTwo simples types

SubstitutionSubstitution One letter is exchanged for anotherOne letter is exchanged for another Some call it monoalphabetic cipher or simple Some call it monoalphabetic cipher or simple

substitutionsubstitution TranspositionTransposition

Order of the letters rearrangedOrder of the letters rearranged

Caesar CipherCaesar 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

Plaintext

Ciphertext

• In this example:• Shift of 3• ci = E(pi) = pi + 3

• What would the ciphertext for UNISEL?• Answer: xqlvho

• TREATY IMPOSSIBLE?• Answer: wuhdwb lpsrvvleoh

PermutationPermutation

Almost like Caesar CipherAlmost like Caesar Cipher Uses a word as the keyUses a word as the key E.g. if ‘word’ is the key:E.g. if ‘word’ is the key:

If ‘professional’ as the key:If ‘professional’ as the key:

If the word has several similar alphabets, If the word has several similar alphabets, only ONE of it should be usedonly ONE of it should be used


w o r d a b c e f g h i j k l m n p q s t u v x y z

Plaintext

Ciphertext


p r o f e s i n a l b c d g h j k m q t u v w x y z

Tmepty adjhqqarce


Encrypt “TREATY IMPOSSIBLE” using Encrypt “TREATY IMPOSSIBLE” using both permutation algorithmsboth permutation algorithms Answer: Answer: spawsy fjmlqqfola Answer: tmepty adjhqqarce


Both types of permutation algorithms may Both types of permutation algorithms may invoke easy access by cryptanalyst, invoke easy access by cryptanalyst, therefore it is more desirable to have less therefore it is more desirable to have less regular rearrangement of lettersregular rearrangement of letters

A possibility is to count by three (or 5, or 7, A possibility is to count by three (or 5, or 7, or 9) and rearrange in that orderor 9) and rearrange in that order



a d g j m p s v y b e h k n q t w z c f i l o r u x

In this case, a+3=d, d+3=g, g+3=jIn this case, a+3=d, d+3=g, g+3=j Encrypt “TREATY IMPOSSIBLE”Encrypt “TREATY IMPOSSIBLE”

Answer: fzmafu yktqccydhm

Vernam CipherVernam Cipher

Involves an arbitrarily long nonrepeating Involves an arbitrarily long nonrepeating sequence of numbers combined with the sequence of numbers combined with the plaintextplaintext

Equate each alphabet with corresponding Equate each alphabet with corresponding number, add to its random 2-digit, find the number, add to its random 2-digit, find the mod of its sum with 26 to get the mod of its sum with 26 to get the ciphertextciphertext



0 1 2 3 4 5 6 7 8 910

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

V E R N A M C I P H E R

76

48

16

82

44

03

58

11

60

05

48

88

21 4

17

13 0

12 2 8

15 7 4

17

97

52

33

95

44

15

60

19

75

12

52

105

19 0 7

17

18

15 8

19

23

12 0 1

t a h r s p I t x m a b

VigenVigenère Cipher ère Cipher

Uses a table called “VigenUses a table called “Vigenèère Tableaure Tableau”” Table is a series of alphabets from A to ZTable is a series of alphabets from A to Z

Encryption is done from top to bottom, following Encryption is done from top to bottom, following the key which follows the the key which follows the ‘‘PermutationPermutation’’ style style keykey

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

A 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

B 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 a

C c 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

X x y z a b c d e f g h i j k l m n o p q r s t u v w

Y y z a b c d e f g h i j k l m n o p q r s t u v w x

Z z 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

TranspositionTransposition

Goal is confusionGoal is confusion Encryption in which the letters of the Encryption in which the letters of the

message are rearranged; breaking message are rearranged; breaking established patternsestablished patterns

Columnar TranspositionColumnar Transposition

Rearranging characters of plaintext into columnsRearranging characters of plaintext into columns In a 5-column transposition, plaintext characters In a 5-column transposition, plaintext characters

are written in rows of five and arranged one row are written in rows of five and arranged one row after another:after another:

Ciphertext is written from column to columnCiphertext is written from column to column

CC11 CC22 CC33 CC44 CC55

CC66 CC77 CC88 CC99 CC1010

CC1111 CC1212 CC1313 CC1212 CCnnplaintext

cipherte

xt


THISITHISISAMESSAMESSAGETSAGETOSHOWOSHOWHOWACHOWACOLUMNOLUMNARTRAARTRANSPOSNSPOSITIONITIONWORKSWORKS

tssoh oaniw haaso lrsto imghw tssoh oaniw haaso lrsto imghw utpir seeoa mrook istwc nasnsutpir seeoa mrook istwc nasns

PUTAN PUTAN XIFWOXIFWORDSDORDSDONOTFINOTFILLALLLLALLCOLUMCOLUMNSXXXNSXXX

pxrnl cnuid olostpxrnl cnuid olostFstal xawdf luxnoFstal xawdf luxnooilmxoilmx

Public Key EncryptionPublic Key Encryption

Each user has a key that does not have to Each user has a key that does not have to be kept secretbe kept secret

Secret is the decryption technique, not the Secret is the decryption technique, not the key itselfkey itself

Public key cryptosystem accomplish this Public key cryptosystem accomplish this goal by using two keys; one to encrypt and goal by using two keys; one to encrypt and one to decryptone to decrypt

Each user has two keys: a public key and Each user has two keys: a public key and a private keya private key


P = D(kP = D(kPRIVPRIV, E(k, E(kPUBPUB, P)), P))

Some public key encryption algorithms Some public key encryption algorithms have this relationship: P=D(khave this relationship: P=D(kPUBPUB, E(k, E(kPRIVPRIV, ,

P))P))


Let’s say there’s 3 users, B, C and DLet’s say there’s 3 users, B, C and D All three have to send a message to A and All three have to send a message to A and

each othereach other Each distinct pair of users needs a key, each Each distinct pair of users needs a key, each

user would need 3 different keys; A would user would need 3 different keys; A would need a key for B, C and D each.need a key for B, C and D each.

With public key, each B, C and D can use A’ s With public key, each B, C and D can use A’ s public key to send the message, but A’s public key to send the message, but A’s private key remains private, so C cannot private key remains private, so C cannot decrypt message sent by B to Adecrypt message sent by B to A

ComparisonComparison

Secret key (Symmetric)Secret key (Symmetric) Public Key (Asymmetric)Public Key (Asymmetric)

Number of KeysNumber of Keys 11 22

Protection of keyProtection of key Must be kept secretMust be kept secret One key must be kept One key must be kept secret, the other can be secret, the other can be freely exposedfreely exposed

Best usesBest uses Cryptographic workhorse; Cryptographic workhorse; secrecy and integrity of secrecy and integrity of data – single characters to data – single characters to blocks of data, messages, blocks of data, messages, filesfiles

Key exchange, Key exchange, authenticationauthentication

Key distributionKey distribution Must be out-of-handMust be out-of-hand Public key can be used to Public key can be used to distribute other keysdistribute other keys

SpeedSpeed FastFast Slow; typically, 10,000 Slow; typically, 10,000 times slower than secret times slower than secret keykey

Rivest-Shamir-Adelman (RSA) Rivest-Shamir-Adelman (RSA) EncryptionEncryption

A public key systemA public key system Introduced in 1978 and remains secure until Introduced in 1978 and remains secure until

nownow Combines results from number theory with Combines results from number theory with

degree of difficulty in determining the prime degree of difficulty in determining the prime factors of a given numberfactors of a given number

Uses two keys, d & e for decryption and Uses two keys, d & e for decryption and encryption – either private or public key can encryption – either private or public key can be used in the encryptionbe used in the encryption

P=E(D(P))=D(E(P))P=E(D(P))=D(E(P))


C=PC=Pee mod n mod n

P=CP=Cdd mod n mod n

P=CP=Cdd mod n = (P mod n = (P

ee))dd mod n = (P mod n = (P

dd))ee mod n mod n

Key choice:Key choice: Consists of pair of integer (e,n) for encryption and Consists of pair of integer (e,n) for encryption and

integer (d,n) for decryptioninteger (d,n) for decryption Start point to find value of nStart point to find value of n

• n should be quite large (a product of two prime numbers n should be quite large (a product of two prime numbers p and q)p and q)

• p and q are usually 100 digits eachp and q are usually 100 digits each• e is relatively prime to (p-1)*(q-1) e is relatively prime to (p-1)*(q-1) e has no factors in e has no factors in

common with (p-1)*(q-1) where e>(p-1) and e>(q-1)common with (p-1)*(q-1) where e>(p-1) and e>(q-1)


e * d = 1 mod (p-1)*(q-1)e * d = 1 mod (p-1)*(q-1) Usually n is made public and d is kept Usually n is made public and d is kept

secretsecret

TOTURIAL CRYPTOGRAPHY Ver :1. Things to learn about Concepts of encryption Cryptanalysis Symmetric encryption Asymmetric encryption Protocols.

Documents

study of encryption

encryption techniques

encryption schemecan

ciphertext p

plaintextcontinuedwhen

symmetric encryptionwhen

message scramblingdecryption

key kwhen c