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Digital Signatures and Certificates

Encryption – Process of converting electronic data into another form, called ciphertext, which cannot be easily understood by anyone except the authorized parties. This assures data security. 
Decryption– Process of translating code to data. 

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Types of Encryption 

Data encryption transforms information into a code that is only accessible to those with a password or secret key, sometimes referred to as a decryption key. Data that has not been encrypted is referred to as plaintext, whereas data that has been encrypted is referred to as ciphertext. In today’s business sector, encryption is one of the most popular and effective data protection solutions. By converting data into ciphertext, which can only be decoded with a special decryption key generated either before or at the time of the encryption, data encryption serves to protect the secrecy of data.



Symmetric Encryption



Asymmetric Encryption

Public key– Key which is known to everyone. Ex-public key of A is 7, this information is known to everyone. 
Private key– Key which is only known to the person who’s private key it is. 
Authentication-Authentication is any process by which a system verifies the identity of a user who wishes to access it. 
Non- repudiation– Non-repudiation is a way to guarantee that the sender of a message cannot later deny having sent the message and that the recipient cannot deny having received the message. 
Integrity– to ensure that the message was not altered during the transmission. 
Message digest -The representation of text in the form of a single string of digits, created using a formula called a one way hash function. Encrypting a message digest with a private key creates a digital signature which is an electronic means of authentication.. 
 

Digital Signature

A digital signature is a mathematical technique used to validate the authenticity and integrity of a message, software, or digital document. 

  1. Key Generation Algorithms: Digital signature is electronic signatures, which assure that the message was sent by a particular sender. While performing digital transactions authenticity and integrity should be assured, otherwise, the data can be altered or someone can also act as if he was the sender and expect a reply.
  2. Signing Algorithms: To create a digital signature, signing algorithms like email programs create a one-way hash of the electronic data which is to be signed. The signing algorithm then encrypts the hash value using the private key (signature key). This encrypted hash along with other information like the hashing algorithm is the digital signature. This digital signature is appended with the data and sent to the verifier. The reason for encrypting the hash instead of the entire message or document is that a hash function converts any arbitrary input into a much shorter fixed-length value. This saves time as now instead of signing a long message a shorter hash value has to be signed and moreover hashing is much faster than signing.
  3. Signature Verification Algorithms : Verifier receives Digital Signature along with the data. It then uses Verification algorithm to process on the digital signature and the public key (verification key) and generates some value. It also applies the same hash function on the received data and generates a hash value. If they both are equal, then the digital signature is valid else it is invalid.

The steps followed in creating digital signature are : 

  1. Message digest is computed by applying hash function on the message and then message digest is encrypted using private key of sender to form the digital signature. (digital signature = encryption (private key of sender, message digest) and message digest = message digest algorithm(message)).
  2. Digital signature is then transmitted with the message.(message + digital signature is transmitted)
  3. Receiver decrypts the digital signature using the public key of sender.(This assures authenticity, as only sender has his private key so only sender can encrypt using his private key which can thus be decrypted by sender’s public key).
  4. The receiver now has the message digest.
  5. The receiver can compute the message digest from the message (actual message is sent with the digital signature).
  6. The message digest computed by receiver and the message digest (got by decryption on digital signature) need to be same for ensuring integrity.

Message digest is computed using one-way hash function, i.e. a hash function in which computation of hash value of a message is easy but computation of the message from hash value of the message is very difficult. 

 

Assurances about digital signatures

The definitions and words that follow illustrate the kind of assurances that digital signatures offer.

  1. Authenticity: The identity of the signer is verified.
  2. Integration: Since the content was digitally signed, it hasn’t been altered or interfered with.
  3. Non-repudiation: demonstrates the source of the signed content to all parties. The act of a signer denying any affiliation with the signed material is known as repudiation.
  4. Notarization: Under some conditions, a signature in a Microsoft Word, Microsoft Excel, or Microsoft PowerPoint document that has been time-stamped by a secure time-stamp server is equivalent to a notarization.

Benefits of Digital Signatures

Drawbacks of Digital Signature

Digital Certificate

Digital certificate is issued by a trusted third party which proves sender’s identity to the receiver and receiver’s identity to the sender. 
A digital certificate is a certificate issued by a Certificate Authority (CA) to verify the identity of the certificate holder. Digital certificate is used to attach public key with a particular individual or an entity. 

Digital certificate contains

Digital certificate is also sent with the digital signature and the message. 

Advantages of Digital Certificate

Disadvantages of Digital Certificate

Digital certificate vs digital signature

Digital signature is used to verify authenticity, integrity, non-repudiation ,i.e. it is assuring that the message is sent by the known user and not modified, while digital certificate is used to verify the identity of the user, maybe sender or receiver. Thus, digital signature and certificate are different kind of things but both are used for security. Most websites use digital certificate to enhance trust of their users
 

Feature Digital Signature Digital Certificate
Basics / Definition A digital signature secures the integrity of a digital document in a similar way as a fingerprint or attachment. Digital certificate is a file that ensures holder’s identity and provides security.
Process / Steps Hashed value of original data is encrypted using sender’s private key to generate the digital signature. It is generated by CA (Certifying Authority) that involves four steps: Key Generation, Registration, Verification, Creation.
Security Services Authenticity of Sender, integrity of the document and non-repudiation. It provides security and authenticity of certificate holder.
Standard It follows Digital Signature Standard (DSS). It follows X.509 Standard Format

Frequently Asked Question on Digital Signatures and Certificates – FAQs

What is a digital signature?

A digital signature is a mathematical technique used to validate the authenticity and integrity of a message, software, or digital document. 

What is a digital certificate?

Digital certificate is issued by a trusted third party which proves sender’s identity to the receiver and receiver’s identity to the sender. 

Can digital signatures be forged?

It is very difficult to forge a digital signature with having private key.

What is a self-signed certificate?

A self-signed certificate is a certificated signed by owns private key rather then trusted third party.

What is a Public Key Infrastructure (PKI)?

The hardware, software, policies, protocols, and procedures needed to generate, manage, distribute, utilise, store, and revoke digital certificates and public keys are collectively referred to as the public key infrastructure, or PKI.


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