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Home/ Blog/ How do I configure Squid to cache content using HTTPS?

How do I configure Squid to cache content using HTTPS?

PYPROXY PYPROXY · May 19, 2025

Squid is a popular open-source proxy server that is widely used for caching web content to improve network performance and reduce bandwidth usage. It supports caching HTTP content, but configuring it for caching HTTPS content requires some additional steps due to the nature of HTTPS traffic. HTTPS encrypts the communication between the client and server, meaning that Squid cannot directly cache the content unless it can decrypt the data. This article will guide you through the process of configuring Squid to cache HTTPS content, including necessary setup, SSL certificate management, and security considerations.

Introduction to Squid Proxy Server

Squid is a widely used caching proxy server that helps improve web performance by caching frequently accessed web content. It is known for its flexibility, scalability, and extensive support for various web protocols, including HTTP, HTTPS, FTP, and more. While Squid can efficiently cache HTTP content, HTTPS caching is more challenging due to the encryption used in HTTPS connections.

When a user makes an HTTPS request, the connection is encrypted using SSL/TLS protocols, which prevents the proxy server from inspecting or caching the content directly. To overcome this limitation, Squid provides a feature called SSL bumping, which allows it to decrypt HTTPS traffic, cache the content, and then re-encrypt the data before forwarding it to the client.

In this article, we will explore how to configure Squid to cache HTTPS content using SSL bumping, focusing on the necessary steps to set it up, manage SSL certificates, and address security concerns.

Prerequisites for Configuring Squid for HTTPS Caching

Before you start configuring Squid to cache HTTPS content, you need to ensure that your system meets the following prerequisites:

1. Squid Installation: Ensure that Squid is installed and running on your system. You can install Squid using your system's package manager or by compiling the source code.

2. SSL Libraries: Since HTTPS involves encryption, Squid requires SSL/TLS libraries such as OpenSSL to handle SSL traffic. Make sure that Squid is compiled with SSL support.

3. SSL Certificates: To decrypt HTTPS traffic, Squid needs to use SSL certificates. You will need a certificate authority (CA) certificate for SSL bumping.

4. Root Access: Configuring Squid to intercept and decrypt SSL traffic requires root privileges, as it involves modifying network settings and managing certificates.

Step-by-Step Guide to Configure Squid for HTTPS Caching

Now that you have met the prerequisites, you can follow these steps to configure Squid for caching HTTPS content.

1. Enable SSL Bumping in Squid Configuration

The first step is to enable SSL bumping in Squid. SSL bumping allows Squid to intercept and decrypt HTTPS traffic. To do this, you need to modify the Squid configuration file (`squid.conf`).

Open the Squid configuration file in a text editor:

```bash

sudo nano /etc/squid/squid.conf

```

Locate the section related to SSL configuration and add the following lines to enable SSL bumping:

```bash

https_port 3129 intercept ssl-bump cert=/etc/squid/ssl_cert/myCA.pem key=/etc/squid/ssl_cert/myCA.key

ssl_bump peek all

ssl_bump bump all

sslproxy_cert_error allow all

sslproxy_flags DONT_VERIFY_PEER

```

Explanation of the configuration:

- `https_port 3129 intercept ssl-bump`: Configures Squid to intercept HTTPS traffic on port 3129.

- `cert` and `key`: Path to your SSL certificate and private key.

- `ssl_bump peek all`: Peeks at all HTTPS traffic to examine the handshake and make decisions about caching.

- `ssl_bump bump all`: Bumps the SSL connection to decrypt the traffic.

- `sslproxy_cert_error allow all`: Allows Squid to ignore SSL certificate errors (optional, but necessary for SSL bumping).

- `sslproxy_flags DONT_VERIFY_PEER`: Tells Squid not to verify the client's certificate during SSL bumping.

2. Generate and Install the SSL Certificate

To decrypt HTTPS traffic, Squid needs a valid SSL certificate. You can either use a self-signed certificate or a certificate from a trusted certificate authority (CA). In this example, we will use a self-signed certificate.

Generate the SSL certificate and private key:

```bash

sudo openssl genpkey -algorithm RSA -out /etc/squid/ssl_cert/myCA.key

sudo openssl req -new -key /etc/squid/ssl_cert/myCA.key -out /etc/squid/ssl_cert/myCA.csr

sudo openssl x509 -req -days 365 -in /etc/squid/ssl_cert/myCA.csr -signkey /etc/squid/ssl_cert/myCA.key -out /etc/squid/ssl_cert/myCA.pem

```

After generating the certificate, you need to install the CA certificate on the client machines that will be using the proxy server. This ensures that the client can trust the Squid proxy when it presents the decrypted content.

3. Configure Access Control for HTTPS Traffic

Squid provides flexible access control mechanisms to define which clients can access the proxy server and cache HTTPS content. You can configure access control rules in the Squid configuration file.

Add the following lines to the `squid.conf` file to allow access to HTTPS traffic:

```bash

acl SSL_ports port 443

acl CONNECT method CONNECT

http_access allow CONNECT SSL_ports

http_access allow all

```

This configuration allows Squid to handle HTTPS traffic (port 443) and allows all clients to access the proxy server. You can modify the `http_access` rules to restrict access to specific clients if necessary.

4. Restart Squid to Apply Changes

Once you have made all the necessary changes to the Squid configuration file, restart Squid to apply the new settings:

```bash

sudo systemctl restart squid

```

This will restart Squid and apply the SSL bumping and HTTPS caching configuration.

Security Considerations for HTTPS Caching

Caching HTTPS content raises some security concerns, as Squid will be decrypting sensitive data. Here are some important security considerations:

1. SSL Certificate Management: The SSL certificate used for bumping must be handled carefully to avoid compromising the security of encrypted traffic. Ensure that the certificate is protected and stored securely.

2. Privacy Concerns: Since Squid decrypts HTTPS traffic, it can potentially inspect sensitive data. Make sure that only trusted administrators have access to the Squid logs and configuration files.

3. Certificate Pinning: Some websites use certificate pinning to prevent man-in-the-middle attacks. Squid may not be able to cache content from these sites, as it cannot properly intercept the encrypted traffic.

4. Legal Implications: Intercepting and decrypting HTTPS traffic can have legal implications, especially if the proxy is deployed in a corporate environment. Ensure that you have proper authorization and compliance with privacy regulations.

Configuring Squid to cache HTTPS content requires additional configuration steps, such as enabling SSL bumping and managing SSL certificates. While this setup can significantly improve network performance by caching frequently accessed HTTPS content, it also comes with security and privacy considerations. By following the steps outlined in this guide, you can successfully configure Squid to cache HTTPS content, helping to reduce bandwidth usage and improve user experience. However, always be mindful of the security implications and ensure proper certificate management and access control to protect sensitive data.

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