What is Digital Signature
Building confidentiality
and trust
into networked transactions.
Adv. Prashant Mali [BSc.(Phy.), MSc.(Comp. Sci.), CNA, LLB]
Cyber Law & IPR Expert
Encryption
It is a technique of converting plain text into ciphertext and reconverting it into plain text.
Basic Techniques of Encryption
• Transposition Cipher
• Substitution Cipher
• Product Cipher
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
Basic Techniques of Encryption- Transposition Cipher
WE WILL ATTACK ON BHAI ON SUNDAY
LL ATWE WI ON BHTACK SUNDAAI ONY
TRANSPOSETRANSPOSE
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
Basic Techniques of Encryption- Substitution Cipher
INDORE IS A GOOD CITY
DKILQS DR M BLLI NDTY
SUBSTITUTESUBSTITUTE
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.
Basic Techniques of Encryption- Product Cipher
INDORE IS A GOOD CITY
DKILQS DR M BLLI NDTY
SUBSTITUTESUBSTITUTE
TRANSPOSETRANSPOSE
S DR DKILQI NDTM BLLY
Elements of Encryption
Encryption method
Decryption methodPlain
textPlain text
Encryption key
DecryptionKeyCipher text
• Encryption Algorithm (function used to encrypt or decrypt)
• Encryption keys (information used to cipher)
Good Encryption System: Features
• Short Key
•Strong Algorithm
•High work factor
•Low error propagation
Encryption
Building confidentiality
and trust
into networked transactions.
CHANGING THE WAY CHANGING THE WAY
OF DOING BUSINESSOF DOING BUSINESS
A MATTER OF TRUST• Building Trust: Direct trust relationship
Using Encryption
Some every day transactions:
Credit Card
Contract
Notarized
NotarizedDocument
MedicalRecords
Why do we place trustin these transactions?
• Authentication
• Confidentiality
• Integrity
• Non-repudiation
Ways of Encryption
Two ways of encryption
Symmetric Key or
Private Key Encryption
Asymmetric Key or Public Key Encryption
(abbreviated as PKI)
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
sdfklj98a475$56jhgv98456vjnf84576FGHH78lfkghj-506#6lkjg4#$5;lkn;t7;lsk%0
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.
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
Public Key SystemOne half of a key pair is used to encrypt,
the other half is used to decrypt.
EncryptionEncryption
Recipient’sPublic
Key
Recipient’sPrivate
Key
DecryptionDecryption
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
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 :
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 :
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
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.
AuthenticationAuthenticationIt ensures :
Non RepudiationNon RepudiationIntegrityIntegrity
Basic MethodologyBasic Methodology
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.
How does PKI work?
OriginalMessage
Encrypted& Signed
Sender’s
Private KeyHash CodeDigital
Signature
Symmetric Key
Recipient’s
Public Key
Encrypted Symmetric
KeySender
Original
Message
How does PKI work?
Encrypted& Signed
Symmetric KeyEncrypted Symmetric
Key
Recipient’s
Private Key
OriginalMessage
Hash Algorithm
Hash CodeDigital Signature
Sender’s
Public Key
Message verified
Recipient
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 PeriodExpires: 31 December 2022
Public Key:
Signed: CA’s Signature
Name: Prashant Mali
Number: 2564567AID Number & Name
A Digital Certificate is a digitally signed document that associates a public key with a user.
Digital Certificate
Key Lifecycle ManagementKey Generation
Certificate Issuance
Key Usage
or
Certificate Validation
Key Expiry
Key Update
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.
