How is the security rating decided?

The tool inspects each component of the suite. NULL ciphers, RC4, MD5, export-grade and anonymous key exchange are marked insecure. 3DES and CBC modes on TLS 1.2 are marked weak. Modern AEAD ciphers such as AES-GCM and ChaCha20-Poly1305 with ephemeral key exchange are marked secure.

What is forward secrecy and why does it matter?

Forward secrecy means a compromise of the server's long-term private key cannot decrypt past recorded sessions. It comes from ephemeral key exchange (ECDHE or DHE). Static RSA or DH suites lack it, which is why they are flagged even when the cipher itself is strong.

Why are TLS 1.3 suites shown without an explicit key exchange?

In TLS 1.3 the cipher suite only names the AEAD cipher and hash. Key exchange and authentication are negotiated separately through other extensions, always using ephemeral key exchange, so every TLS 1.3 suite has forward secrecy by design.

What is the difference between AEAD and CBC ciphers?

AEAD ciphers such as AES-GCM and ChaCha20-Poly1305 combine encryption and integrity in one operation and resist padding-oracle attacks. CBC mode in TLS 1.2 separates encryption from a MAC and has a history of padding-oracle issues, so AEAD is preferred.

Is anything sent to a server?

No. The decoding and rating run entirely in your browser against a bundled subset of the IANA registry. Nothing you enter is transmitted.

TLS Cipher Suite Decoder

A TLS cipher suite name packs four decisions into one string: how keys are exchanged, how the server is authenticated, which bulk cipher encrypts the data, and which hash provides integrity. This tool unpacks any suite and tells you whether it still meets modern guidance or should be retired.

How it works

You can enter either the IANA name (for example TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) or the two-byte hex code (for example 0xC02F). The tool resolves one form to the other using a bundled slice of the IANA registry, then parses the components:

Protocol family — TLS 1.3 suites (TLS_AES_*, TLS_CHACHA20_*) name only the AEAD cipher and hash; older suites name the full key-exchange and authentication pair.
Key exchange / authentication — ECDHE and DHE provide forward secrecy; static RSA, ECDH and DH do not; anonymous variants provide no authentication at all.
Bulk cipher — AES-GCM, ChaCha20-Poly1305 and AES-CCM are modern AEAD; AES-CBC, 3DES, RC4 and NULL are flagged in increasing order of severity.
MAC / hash — SHA-256/384 are fine, SHA-1 is legacy, and MD5 is broken.

It then applies BSI/NIST-aligned rules to produce an overall rating with specific reasons.

Example and notes

Decode 0x0005 and the tool resolves it to TLS_RSA_WITH_RC4_128_SHA and rates it insecure, citing RC4 being prohibited and static RSA lacking forward secrecy. Decode 0x1303 and you get TLS_CHACHA20_POLY1305_SHA256, rated secure as a modern TLS 1.3 AEAD suite.

The bundled registry covers the suites you meet in real server configurations. For an exhaustive list consult the full IANA TLS parameters registry, but the ratings here reflect current deployment guidance.