Merge branch 'docs-security-tls-support' into 'master'

Add docs TLS support details for GitLab

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/166273



Merged-by: Brendan Lynch <blynch@gitlab.com>
Approved-by: Stan Hu <stanhu@gmail.com>
Reviewed-by: Achilleas Pipinellis - OOO until November 25th (parental leave) <axil@gitlab.com>
Reviewed-by: Peter Lu <plu@gitlab.com>
Co-authored-by: Achilleas Pipinellis <axil@gitlab.com>
Co-authored-by: Hossein Pursultani <hpursultani@gitlab.com>

doc/security/tls_support.md

+---
+stage: Govern
+group: Authentication
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://handbook.gitlab.com/handbook/product/ux/technical-writing/#assignments
+---
+
+# TLS support
+
+DETAILS:
+**Tier:** Free, Premium, Ultimate
+**Offering:** GitLab.com, Self-managed, GitLab Dedicated
+
+GitLab prioritizes the security of data transmission between users and our
+platforms by employing Transport Layer Security (TLS) to safeguard information
+as it travels across the internet.
+
+As cybersecurity threats continue to evolve, GitLab remains committed to maintaining the
+highest standards of security. We regularly update our TLS support to ensure
+that all communications with GitLab services are protected using the most secure
+and up-to-date encryption methods available.
+
+This document outlines the current TLS support in GitLab, including the versions
+and cipher suites we use to keep your data safe and secure.
+
+## Supported protocols
+
+GitLab supports TLS 1.2 and higher versions for secure communications. This
+means that TLS 1.2 and TLS 1.3 are fully supported and recommended for use with
+GitLab.
+
+Older protocols such as TLS 1.1, TLS 1.0, and all versions of SSL are not
+supported due to known security vulnerabilities. By enforcing the use of TLS 1.2
+and higher, GitLab ensures a high level of security for all data transmissions
+and interactions with the platform.
+
+## Supported cipher suites
+
+GitLab supports the following cipher suites and protocol versions:
+
+| Protocol Version | Cipher Suite | [Grade](https://github.com/ssllabs/research/wiki/SSL-Server-Rating-Guide) |
+|------------------|--------------|-------|
+| TLSv1.3 | TLS_AKE_WITH_AES_128_GCM_SHA256 | A |
+| TLSv1.3 | TLS_AKE_WITH_AES_256_GCM_SHA384 | A |
+| TLSv1.3 | TLS_AKE_WITH_CHACHA20_POLY1305_SHA256 | A |
+| TLSv1.2 | TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 | A |
+| TLSv1.2 | TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 | A |
+| TLSv1.2 | TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256-draft | A |
+| TLSv1.2 | TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA | A |
+| TLSv1.2 | TLS_RSA_WITH_AES_128_GCM_SHA256 | A |
+| TLSv1.2 | TLS_RSA_WITH_AES_128_CBC_SHA | A |
+| TLSv1.2 | TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 | A |
+| TLSv1.2 | TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA | A |
+| TLSv1.2 | TLS_RSA_WITH_AES_256_GCM_SHA384 | A |
+| TLSv1.2 | TLS_RSA_WITH_AES_256_CBC_SHA | A |
+| TLSv1.2 | TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 | A |
+| TLSv1.2 | TLS_RSA_WITH_AES_128_CBC_SHA256 | A |
+| TLSv1.2 | TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 | A |
+| TLSv1.2 | TLS_RSA_WITH_AES_256_CBC_SHA256 | A |
+
+## Certificate requirements
+
+OpenSSL 3 increased the [default security level from level 1 to 2](https://docs.openssl.org/3.0/man3/SSL_CTX_set_security_level/#default-callback-behaviour),
+raising the number of bits of security from 80 to 112. As a result, RSA, DSA, and
+DH keys shorter than 2048 bits and ECC keys shorter than 224 bits are
+prohibited. GitLab will fail to connect to a service that uses a certificate
+signed with insufficient bits with a `certificate key too weak` error message.
+
+We strongly recommend using at least 128 bits of security. This means using RSA,
+DSA, and DH keys with at least 3072 bits, and ECC keys longer than 256 bits.
+
+| Key type | Key length (bits) | Status      |
+|----------|-------------------|-------------|
+| RSA      | 1024              | Prohibited  |
+| RSA      | 2048              | Supported   |
+| RSA      | 3072              | Recommended |
+| RSA      | 4096              | Recommended |
+| DSA      | 1024              | Prohibited  |
+| DSA      | 2048              | Supported   |
+| DSA      | 3072              | Recommended |
+| ECC      | 192               | Prohibited  |
+| ECC      | 224               | Supported   |
+| ECC      | 256               | Recommended |
+| ECC      | 384               | Recommended |
+
+## OpenSSL version and TLS requirements
+
+GitLab 17.7 and later use OpenSSL version 3. All components that are shipped
+with the Linux package are compatible with OpenSSL 3. However, before upgrading
+to GitLab 17.7, use the [OpenSSL 3 guide](https://docs.gitlab.com/omnibus/settings/ssl/openssl_3.html)
+to identify and assess the compatibility of your external integrations.