TLS_PSK_WITH_AES_128_CCM_8

What each component means

A cipher suite names the algorithms a client and server agree on in one handshake. TLS_PSK_WITH_AES_128_CCM_8 combines PSK key exchange, PSK authentication, AES-128-CCM-8 encryption and AEAD integrity protection. Each part is explained below with its known weaknesses; for the bigger picture see how cipher suites work.

Key exchange and authentication: pre-shared key (PSK), defined in RFC 4279 (2005). Both sides already hold the same symmetric secret, provisioned out of band, and the handshake only names which key to use (the PSK identity). No certificates and no public-key operations are needed, which is why PSK suites appear in constrained devices and closed systems rather than on the public web. Plain PSK has no forward secrecy: whoever learns the key can decrypt every session made with it.

Encryption: AES with a 128-bit key, the 128-bit block cipher of FIPS 197 (2001). Most server and phone CPUs have AES instructions (AES-NI on x86, the ARMv8 cryptography extensions), which make it fast and avoid the cache-timing leaks of table-based software implementations.

Mode: CCM_8, AES-CCM with the authentication tag cut from 16 to 8 bytes (RFC 6655). That saves 8 bytes per record on constrained links, but a forged record now passes with probability 2^-64 per attempt instead of 2^-128, and no CCM_8 suite is marked Recommended in the IANA registry.

Integrity: there is no separate MAC because the AEAD tag authenticates every record. The SHA256 at the end of the name selects the TLS 1.2 PRF hash used to derive keys and compute the Finished messages.

Why this rating

ssl.sh rating: Weak. The reasons:

• No forward secrecy: the session keys are protected by the server's long-term key (static RSA/DH/ECDH, PSK or Kerberos), so a leaked key decrypts recorded traffic.

How ssl.sh rates cipher suites

Which TLS libraries support it

Support for TLS_PSK_WITH_AES_128_CCM_8 as read from each library's own source code or official documentation on 2026-11-10. “Enabled by default” means the library negotiates it with no configuration; “off by default” means it is implemented but has to be switched on.

None of the 9 libraries tracked here enables it by default. Also implemented by: OpenSSL 3.5 and GnuTLS.

NSS shows the library's own defaults; Firefox switches every NSS suite off at start-up and re-enables only those with a security.ssl3.* or security.tls13.* preference. Java defaults are derived from the jdk.tls.disabledAlgorithms value Oracle documents for JDK 21, which later updates may extend. The OpenSSL and GnuTLS rows only show whether the suite is implemented.

History and standards status

TLS_PSK_WITH_AES_128_CCM_8 (0xC0,0xA8) is registered in the IANA TLS Cipher Suites registry with RFC 6655, “AES-CCM Cipher Suites for Transport Layer Security (TLS)” (July 2012, Standards Track) as its specification. The registry marks it N, which per RFC 8447 (2018) means it either hasn't been through the IETF consensus process, has limited applicability or is meant only for specific use cases, not necessarily that it is flawed.

Enable or disable it in Nginx and Apache

Disable

Either leave the suite out of your list or exclude it explicitly with a leading "!". Reload the server afterwards (nginx -s reload, apachectl graceful).

# Nginx
ssl_ciphers 'ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:!PSK-AES128-CCM8';

# Apache httpd (mod_ssl)
SSLCipherSuite ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:!PSK-AES128-CCM8

How to test whether a server accepts it

Offer only TLS_PSK_WITH_AES_128_CCM_8 with openssl s_client; if the handshake completes, the server accepts it:

openssl s_client -connect example.com:443 -tls1_2 -cipher PSK-AES128-CCM8 </dev/null

If the handshake succeeds, the server accepts the suite; "no cipher match" or a handshake failure means it doesn't.

nmap's ssl-enum-ciphers script connects repeatedly, trying one suite at a time, and lists every suite the server accepts with a grade from A to F. Look for TLS_PSK_WITH_AES_128_CCM_8 in its output:

nmap --script ssl-enum-ciphers -p 443 example.com

To decode a name or hex code, use the cipher suite lookup; the SSL checker shows which protocol versions a live server accepts and the cipher suite it negotiates.