TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305_SHA256

What each component means

A cipher suite names the algorithms a client and server agree on in one handshake. TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305_SHA256 combines ECDHE key exchange, PSK authentication, ChaCha20-Poly1305 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: ECDHE_PSK. A pre-shared key authenticates the peers and an ephemeral ECDHE share is combined with it, giving forward secrecy without certificates. The first ECDHE_PSK suites came in RFC 5489 (2009); AES-GCM and AES-CCM versions for TLS 1.2 followed in RFC 8442 (2018).

Encryption: ChaCha20-Poly1305, an AEAD pairing the ChaCha20 stream cipher (256-bit key) with the Poly1305 authenticator and a 16-byte tag. It is fast and constant-time in plain software, so it is the usual choice for devices without AES instructions. RFC 7905 (2016) brought it to TLS 1.2 and builds the 96-bit nonce by XORing the padded record sequence number with the sender's write IV, so no explicit nonce is sent with each record.

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: Secure. The reasons:

• Ephemeral key exchange (forward secrecy) plus an AEAD cipher, the combination TLS 1.2 best practice asks for.

How ssl.sh rates cipher suites

Which TLS libraries support it

Support for TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305_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.

Enabled by default in 1 of the 9 libraries tracked here: BoringSSL. 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_ECDHE_PSK_WITH_CHACHA20_POLY1305_SHA256 (0xCC,0xAC) is registered in the IANA TLS Cipher Suites registry with RFC 7905, “ChaCha20-Poly1305 Cipher Suites for Transport Layer Security (TLS)” (June 2016, Standards Track) as its specification. The registry marks it Recommended (Y).

Enable or disable it in Nginx and Apache

Enable

Both servers use OpenSSL names. The snippet keeps a modern list and adds this suite; TLS 1.3 suites are configured separately from the TLS 1.2 list.

# Nginx
ssl_protocols TLSv1.2 TLSv1.3;
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:ECDHE-PSK-CHACHA20-POLY1305';
ssl_prefer_server_ciphers off;

# Apache httpd (mod_ssl)
SSLProtocol -all +TLSv1.2 +TLSv1.3
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:ECDHE-PSK-CHACHA20-POLY1305
SSLHonorCipherOrder off

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:!ECDHE-PSK-CHACHA20-POLY1305';

# 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:!ECDHE-PSK-CHACHA20-POLY1305

How to test whether a server accepts it

Offer only TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305_SHA256 with openssl s_client; if the handshake completes, the server accepts it:

openssl s_client -connect example.com:443 -tls1_2 -cipher ECDHE-PSK-CHACHA20-POLY1305 </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_ECDHE_PSK_WITH_CHACHA20_POLY1305_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.