Digital Certificates:
A digital certificate is an electronic document that uses a digital signature to bind a public key with an entity’s identity (such as a person, organization, or server).
- It acts as a digital passport that verifies the legitimacy of the public key holder.
- It is issued by a Certificate Authority (CA) and follows the X.509 standard.
Digital certificates are part of a Public Key Infrastructure (PKI) and are primarily used to:
- Authenticate the identity of an entity (like a website or email sender),
- Ensure secure communication over the internet,
- And validate the legitimacy of a public key being shared.
They are issued and digitally signed by a Certificate Authority (CA) – a trusted third party that vouches for the identity of the certificate holder.
Why Digital Certificates Are Important:
- Authentication: Prove that a website or system is genuine (e.g., “https://” with a padlock symbol).
- Confidentiality: Enable encrypted communications (like in SSL/TLS).
- Data Integrity: Ensure that transmitted data hasn’t been altered in transit.
- Non-repudiation: Prevent denial of sending or receiving a message.
X.509 Certificates:
X.509 certificates are the standard format for public key certificates defined by the International Telecommunication Union (ITU).
- These certificates are widely used in security protocols like SSL/TLS, HTTPS, and PKI.
- The X.509 certificate structure defines how certificates should be formatted and what fields they must contain, making it a global standard for digital certificate creation and usage.
Key Components of a Digital/X.509 Certificate:
- Subject: The identity of the entity (person, organization, domain) to which the certificate is issued.
- Public Key: The public key that corresponds to the entity’s private key.
- Issuer: The Certificate Authority (CA) that issued and signed the certificate.
- Serial Number: A unique number assigned by the CA to identify the certificate.
- Validity Period: The start and end date that defines the certificate’s lifespan.
- Signature Algorithm: The algorithm used by the CA to sign the certificate (e.g., SHA-256 with RSA).
- Digital Signature: The CA’s digital signature, used to verify that the certificate has not been tampered with.
🌐 Real-World Example:
- When you visit a secure website like https://www.bank.com:
- Your browser receives the site’s X.509 digital certificate.
- It checks if the certificate was issued by a trusted CA (like DigiCert or Let’s Encrypt).
- It validates the certificate’s expiration date and digital signature.
- If everything checks out, it uses the public key from the certificate to start an encrypted SSL/TLS session with the server.
