TLS_PSK_WITH_NULL_SHA256

What each component means

A cipher suite names the algorithms a client and server agree on in one handshake. TLS_PSK_WITH_NULL_SHA256 combines PSK key exchange, PSK authentication, NULL encryption and SHA256 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: none. Records are only protected by the SHA256 MAC, so anyone on the path can read the plaintext. RFC 9325 (2022) says implementations MUST NOT negotiate NULL-encryption suites, while noting they can still be useful for testing and debugging.

Integrity: HMAC-SHA256 over each record, computed before encryption (MAC-then-encrypt). In TLS 1.2 the SHA256 in the name also selects the PRF hash. Because of that, the suite needs TLS 1.2 and cannot be used with older versions.

Why this rating

ssl.sh rating: Insecure. The reasons:

• No encryption (NULL cipher): traffic is sent in clear text.

How ssl.sh rates cipher suites

Which TLS libraries support it

Support for TLS_PSK_WITH_NULL_SHA256 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. Supported but off by default in: Windows Schannel (Windows 11 / Server 2022). 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_NULL_SHA256 (0x00,0xB0) is registered in the IANA TLS Cipher Suites registry with RFC 5487, “Pre-Shared Key Cipher Suites for TLS with SHA-256/384 and AES Galois Counter Mode” (March 2009, Standards Track) as its specification. RFC 9325 (2022), part of BCP 195, says implementations MUST NOT negotiate suites with NULL encryption. The registry marks it D (discouraged), a value introduced by RFC 9847 (2025).

Enable or disable it in Nginx and Apache

This suite is rated insecure, so we don't show how to enable it. Make sure it's excluded.

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-NULL-SHA256';

# 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-NULL-SHA256

How to test whether a server accepts it

Offer only TLS_PSK_WITH_NULL_SHA256 with openssl s_client; if the handshake completes, the server accepts it:

openssl s_client -connect example.com:443 -tls1_2 -cipher PSK-NULL-SHA256 </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_NULL_SHA256 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.