What is digital signature or DSC

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.

Thank YouQuestions

Contact:

prashant.mali@cyberlawconsulting.com

cyberlawconsulting@gmail.com Cell: 9821763157