Public-Private Key Encryption: Driving the HTTPS Handshake & How to Create SSL Certs via OpenSSL CSR

The secure padlock icon in your browser and the ‘S’ in HTTPS signify a protected connection, but what’s the magic behind it? The core technology enabling this security is Public-Private Key Encryption, also known as asymmetric cryptography. It’s the fundamental engine that powers the crucial HTTPS Handshake and underpins the entire process to create ssl certificates for your website.

Understanding how Public-Private Key Encryption works demystifies the steps involved in securing your site, including using tools like OpenSSL to Generate a CSR (Certificate Signing Request). This post breaks down this essential cryptographic concept and shows how it connects directly to obtaining and using an SSL/TLS certificate from providers like SSLRepo.

Key Takeaways

• Public-Private Key Encryption: Uses a mathematically linked key pair: a public key (shareable) for encryption/signature verification, and a private key (secret) for decryption/signature creation.
• Role in HTTPS Handshake: Essential for securely exchanging a symmetric session key and authenticating the server at the start of a secure connection. The server’s public key is shared via its SSL certificate.
• Creating an SSL Certificate: This process starts with generating a key pair (public and private).
• OpenSSL Generate CSR: OpenSSL is a widely used tool to generate the key pair and the Certificate Signing Request (CSR). The CSR contains the public key and your verified identity information.
• CSR Purpose: The CSR is submitted to a Certificate Authority (CA) or reseller (SSLRepo) to request the official SSL certificate.
• Certificate Issuance: The CA verifies the information in the CSR and, upon success, issues the signed SSL certificate, binding your identity to your public key. This certificate is then installed on your server alongside your private key.

Understanding Public-Private Key Encryption

At its heart, Public-Private Key Encryption solves a major challenge: how to share secret information or verify identity over an insecure network (like the internet) without pre-sharing a secret code. It achieves this using two distinct keys:

1. Public Key: This key can be distributed freely. Anyone can use it to encrypt messages intended only for the holder of the corresponding private key, or to verify signatures made by the private key. It’s typically embedded within your SSL certificate.
2. Private Key: This key must be kept absolutely secret by its owner. It’s the only key capable of decrypting messages encrypted with the public key, and it’s used to create digital signatures proving identity.

The Core Principles:

• Encryption/Decryption: Data encrypted with the public key can only be decrypted by the matching private key.
• Digital Signatures: Data “signed” with the private key can be verified using the public key. This confirms the data originated from the private key holder and hasn’t been tampered with.

Common algorithms include RSA and ECC (Elliptic Curve Cryptography).^^[OpenSSL documentation provides extensive details on these algorithms and key generation. openssl.org/docs/ ]^^

The Role in the HTTPS Handshake

The HTTPS Handshake is the initial negotiation between a client (like your browser) and a server to establish a secure connection. Public-Private Key Encryption is critical during these initial steps:

1. Server Authentication: The server sends its SSL certificate to the client. This certificate contains the server’s public key and identity information, signed by a trusted CA.
2. Client Verification: The client verifies the certificate’s signature using the CA’s public key (pre-installed in the browser/OS) and checks if the certificate is valid and matches the domain.
3. Secure Key Exchange: The client generates a temporary secret key (a symmetric session key). It encrypts this session key using the server’s public key (obtained from the certificate).
4. Server Decryption: The encrypted session key is sent to the server. Only the server, possessing the corresponding private key, can decrypt it.
5. Secure Session Established: Both client and server now share the same secret session key. They switch to faster symmetric encryption using this key for the remainder of the communication.

Essentially, the asymmetric Public-Private Key Encryption is used to securely establish the initial trust and exchange the key needed for ongoing symmetric encryption.

Practical Steps: Create SSL Cert via OpenSSL Generate CSR

Getting an SSL certificate to enable HTTPS involves putting Public-Private Key Encryption into practice. Here’s a typical workflow using the common OpenSSL toolkit:

Step 1: Generate the Key Pair

Before anything else, you need your unique public and private keys.

• Action: Use a command like openssl genrsa -out yourdomain.key 2048 (for RSA keys) in your server’s command line.
• Result: This creates your private key file (e.g., yourdomain.key). The corresponding public key is derived from this.
• Critical: Secure your private key! Never share it. It should reside securely on your web server.

Step 2: OpenSSL Generate CSR (Certificate Signing Request)

Now, you need to create a formal request for your certificate.

• Action: Use a command like openssl req -new -key yourdomain.key -out yourdomain.csr.
• Process: OpenSSL will prompt you for information to embed in the CSR. This includes:
  • Common Name (CN): Your fully qualified domain name (e.g., www.yourdomain.com). This must match exactly.
  • Organization Name (O)
  • Organizational Unit (OU)
  • City/Locality (L)
  • State/Province (ST)
  • Country Name (C)
• Result: This generates the CSR file (e.g., yourdomain.csr). It contains your public key and the identifying information you entered, digitally signed implicitly by linking to your private key.

Step 3: Submit CSR to CA & Verification (create ssl cert Part 1)

The CSR is the package you send to get your official certificate.

• Action: Purchase an SSL certificate from a provider like SSLRepo and submit the content of your .csr file during the ordering process.
• Verification: The Certificate Authority (CA) performs validation based on the certificate type (DV, OV, EV). This confirms you own the domain (DV) and potentially verifies your organization’s details (OV/EV).

Step 4: Receive and Install Certificate (create ssl cert Part 2)

Once verification is complete, the CA issues your certificate.

• Action: The CA sends you the signed SSL certificate file (e.g., yourdomain.crt or .pem), often along with intermediate CA certificates (a chain/bundle file).
• Installation: You install the received certificate file(s) and your original private key (yourdomain.key) on your web server (Apache, Nginx, IIS, etc.) according to its specific configuration requirements.
• Result: Your server can now use the certificate and private key to perform the HTTPS Handshake, proving its identity and enabling encrypted connections.

Why This Matters

Understanding Public-Private Key Encryption clarifies why these steps are necessary. The CSR generated by OpenSSL formally presents your public key and identity for verification. The CA’s signature on the issued certificate provides trusted validation that the public key truly belongs to the entity controlling the domain. This trust is essential for secure communication established during the HTTPS Handshake.

Wrapping It Up

Public-Private Key Encryption is the cryptographic powerhouse enabling secure online interactions. It’s the crucial mechanism behind the HTTPS Handshake, allowing for server authentication and the secure exchange of session keys. Practically, generating your key pair and using tools like OpenSSL to Generate a CSR are essential first steps to create ssl certificates. By submitting this CSR to a trusted provider like SSLRepo and installing the resulting certificate, you leverage this powerful technology to secure your website and build user trust.

Frequently Asked Questions (FAQ)

Q1: What is Public-Private Key Encryption in simple terms?
A: It’s a security method using two keys: a public one you can share, and a private one you keep secret. If someone encrypts something with your public key, only your private key can decrypt it. This allows secure communication and identity verification.

Q2: How is Public-Private Key Encryption used in the HTTPS Handshake?
A: It’s used initially to verify the server’s identity (via the certificate containing its public key) and to securely exchange a secret session key (by encrypting it with the server’s public key, so only the server’s private key can decrypt it).

Q3: What is a CSR (Certificate Signing Request)?
A: A CSR is a block of encoded text containing your server’s public key and identifying information (like your domain name and organization). It’s generated (often using OpenSSL) and sent to a Certificate Authority to request an SSL certificate.

Q4: Why do I need to use OpenSSL Generate CSR?
A: OpenSSL is a standard, powerful tool for creating the necessary key pair and the CSR file in the correct format required by Certificate Authorities to issue your SSL certificate. While some hosting panels automate this, understanding OpenSSL is useful for manual configurations or troubleshooting.

Q5: What’s the difference between my private key, public key, and SSL certificate?
A:
* Private Key: Your secret key, kept on the server, used for decryption and signing.
* Public Key: Derived from the private key, shared publicly (often in the CSR and certificate), used for encryption and signature verification.
* SSL Certificate: An electronic document issued by a CA that binds your public key to your verified identity (domain/organization) and is signed by the CA to prove its authenticity.

Q6: How do I actually “create ssl cert”?
A: You don’t typically “create” the final trusted certificate yourself. You: 1. Generate a key pair and CSR (e.g., using OpenSSL Generate CSR). 2. Submit the CSR to a CA/reseller (SSLRepo). 3. The CA verifies you and issues (creates) the signed certificate. 4. You install this issued certificate and your private key on your server.