When your browser connects to a website over HTTPS, the two sides negotiate which algorithms they'll use to secure the connection. The result — the cipher suite — defines how the connection is encrypted.

Not all cipher suites are equally secure. Some are safe. Others were broken years ago.

What a cipher suite contains

A cipher suite combines four things:

  1. Key exchange algorithm — how the two sides agree on a shared key (e.g., ECDHE, RSA)
  2. Authentication algorithm — how the server proves its identity
  3. Bulk encryption algorithm — how data is encrypted (e.g., AES-256-GCM)
  4. Message authentication — how message integrity is verified (e.g., SHA-256)

A name like TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 encodes all four.

Which are unsafe

Avoid entirely: - Anything with RC4 — broken, can be decrypted - Anything with DES or 3DES — vulnerable to SWEET32 attack - Anything with export in the name — deliberately weakened (FREAK, Logjam attacks) - Anything with NULL — no encryption at all - RSA key exchange without forward secrecy

Prefer: - ECDHE for key exchange — provides forward secrecy - AES-GCM for bulk encryption - SHA-256 or SHA-384 for the MAC

Why forward secrecy matters

With forward secrecy (ECDHE), each session uses a unique key that's discarded after use. Even if an attacker steals your private key later, they can't decrypt past sessions they recorded. Without it, a single key compromise can expose all historical traffic.

threatprobe.app's Basic report includes a full cipher suite enumeration — every cipher your server offers is listed and insecure ones flagged.

Run a full TLS audit →