4. Basic Techniques of Encryption- Transposition Cipher
Encrypts by changing the order of characters in
the text.
• e.g. : Replace 1st character with 6th
• 2nd with 7th
• 3rd with 8th
• 4th with 9th
• 5th with 10th and so on
5. Basic Techniques of Encryption- Transposition Cipher
WE WILL ATTACK ON BHAI ON SUNDAY
LL ATWE WI ON BHTACK SUNDAAI ONY
TRANSPOSETRANSPOSE
6. Basic Techniques of Encryption- Substitution Cipher
Encrypts by replacing the characters in the text with
characters in a “Key” on the basis of some rule. e.g. :
• Key is “MANISH” and Rule is Replace all
• A in the text with M
• B with A
• C with N
• D with I
• E with S
• F with H
• G with A and so on
7. Basic Techniques of Encryption- Substitution Cipher
INDORE IS A GOOD CITY
DKILQS DR M BLLI NDTY
SUBSTITUTESUBSTITUTE
8. Basic Techniques of Encryption- Product Cipher
Combination of Transposition and Substitution
• Take a Key
• replace the characters in the text with characters in
the Key.
• Transpose the result.
9. Basic Techniques of Encryption- Product Cipher
INDORE IS A GOOD CITY
DKILQS DR M BLLI NDTY
SUBSTITUTESUBSTITUTE
TRANSPOSETRANSPOSE
S DR DKILQI NDTM BLLY
13. A MATTER OF TRUST
• Building Trust: Direct trust relationship
Using Encryption
14. Some every day transactions:
Credit Card
Contract
Notarized
Notarized
Document
Medical
Records
Why do we place trust
in these transactions?
• Authentication
• Confidentiality
• Integrity
• Non-repudiation
15. Ways of Encryption
Two ways of encryption
Symmetric Key or
Private Key Encryption
Asymmetric Key or
Public Key Encryption
(abbreviated as PKI)
16. Symmetric Cryptosystem
Also called private key infrastructure
Cleartext Message Cipher Text Cleartext Message
DES | RC4 DES | RC4Four score and
seven years
ago, our
forefathers
brought forth
the proposition
Four score and
seven years
ago, our
forefathers
brought forth
the proposition
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17. Symmetric Cryptosystem
• Similar key is used for
encryption and decryption
• Both parties should know
the same key
Original
Message
Original
Message
Encrypted
Message
Encrypted
Message
Also called private key infrastructure
Secured transmission of encryption key to other person is a problem.
18. Asymmetric Cryptosystem
Also called Public Key Infrastructure (PKI)
Improvement over Private Key System
Provides all elements expected from a secure transaction :
• Authentication
• Confidentiality
• Integrity
• Non-repudiation
Accordingly generates :
• Signed message
• Secret message
• Signed and Secret message
19. Public Key System
One half of a key pair is used to encrypt,
the other half is used to decrypt.
EncryptionEncryption
Recipient’s
Public
Key
Recipient’s
Private
Key
DecryptionDecryption
20. Public Key Infrastructure(PKI)
Uses a pair of keys.
One part of pair is used for encryption
Another part is used for decryption
One part is kept private (called private key of a person) and
another is made public (called public key of a person)
Any key (public or private) can be used for encryption and
then another is used for decryption
Same key can not be used for encryption and decryption
both. There has to be combination of both keys.
Basic MethodologyBasic Methodology
21. Public Key Infrastructure(PKI)
To generate a secret message
Message is encrypted by
sender with Receiver’s public
key and
It is decrypted by receiver
with his private key.
How messages are generatedHow messages are generated
Original
Message
Encrypted
Message
Receiver’s public key
Encrypted
Message
Original
Message
Receiver’s private key
Encryption
Decryption
• ConfidentialityConfidentiality • IntegrityIntegrity
It ensures :
22. Public Key Infrastructure(PKI)
To generate a signed message
Message is encrypted by
sender with Sender’s private key
and
It is decrypted by receiver
with Sender’s public key.
How messages are generatedHow messages are generated
Original
Message
Encrypted
Message
Sender’s private key
Encrypted
Message
Original
Message
Sender’s public key
Encryption
Decryption
• AuthenticationAuthentication • Non RepudiationNon Repudiation
It ensures :
23. Asymmetric Cryptosystem
Original
Message
Encrypted
Message I
Sender’s private key
Encrypted
Message II
Receiver’s public key
Encrypted
Message II
Encrypted
Message I
Original
Message
Sender’s public key Receiver’s private
key
To generate a signed and
secret message :
Message is first encrypted
by sender with Sender’s
private key.
This encrypted message is
again encrypted with
Receiver’s public key
It is decrypted by receiver
first with his private key and
then with sender’s public key.
How messages are generatedHow messages are generated
It ensures :
AuthenticationAuthentication Non RepudiationNon RepudiationIntegrityIntegrityConfidentialityConfidentiality
24. Digital Signatures
• Digital signatures are hash code of a document
encrypted with sender’s private key.
• For sending the message, first hash code of message is
generated.
• This hash code is encrypted using sender’s private key.
• The message is sent along with encrypted hash code.
• At other end, receiver decrypts hash code with sender’s
public key.
• He also on his own calculates hash code of the message
received.
• Two hash codes should tally.
AuthenticationAuthentication
It ensures :
Non RepudiationNon RepudiationIntegrityIntegrity
Basic MethodologyBasic Methodology
25. Digital Signatures
• In earlier process, message has been sent in clear text
form thus confidentiality has not been achieved.
• To overcome this problem, message and encrypted hash
code may be encrypted by a symmetric key.
• This symmetric key is also then encrypted with
receiver’s public key.
• All these i.e. Message and encrypted hash code which
are now encrypted with symmetric key and symmetric
key itself which is now encrypted with receiver’s public
key, are sent to receiver.
• Receiver first decrypt the symmetric key with his private
key and then decrypt message and hash code with this
symmetric key.
26. How does PKI work?
Original
Message
Encrypted
& Signed
Sender’s
Private KeyHash Code
Digital
Signature
Symmetric Key
Recipient’s
Public Key
Encrypted
Symmetric
KeySender
Original
Message
27. How does PKI work?
Encrypted
& Signed
Symmetric KeyEncrypted
Symmetric
Key
Recipient’s
Private Key
Original
Message
Hash
Algorithm
Hash CodeDigital
Signature
Sender’s
Public Key
Message
verified
Recipient
28. private
Certificate ties a
participant to public key
The authenticity of the
certificate is guaranteed
by the digital signature
generated using the
CA’s private key.
Validity Period
Expires: 31 December 2022
Public Key:
Signed: CA’s
Signature
Name: Prashant Mali
Number: 2564567A
ID Number & Name
A Digital Certificate is a digitally signed document
that associates a public key with a user.
Digital Certificate
30. Encryption Standard
Data Encryption standard
• A short key, strong algorithm system
• Uses a 64 bit key, 56 bits for algorithm and 8 bits are
parity
RSA (Rivest, Shamir, Adalman)
• Public key system.
• Once private key is used to encrypt, it can be
decrypted only using its public key and vice-versa.