TLS_DHE_RSA_WITH_AES_256_GCM_SHA384

What each component means

A cipher suite names the algorithms a client and server agree on in one handshake. TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 combines DHE key exchange, RSA authentication, AES-256-GCM 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: DHE, ephemeral finite-field Diffie-Hellman. A new DH key pair per handshake gives forward secrecy, but in TLS 1.2 the server alone picks the group and the client cannot ask for a stronger one; RFC 7919 (2016) added negotiated FFDHE groups, which saw little uptake. Logjam (CVE-2015-4000, 2015) broke servers that still accepted 512-bit export groups and showed that huge numbers of sites shared the same few 1024-bit primes, and the Raccoon timing attack (2020) exploits how TLS 1.2 strips leading zero bytes from the DH secret. Those are the reasons RFC 9325 (2022) gives for telling TLS 1.2 implementations not to negotiate TLS_DHE_* suites.

Authentication: the server proves its identity with an RSA certificate, signing the handshake's key-exchange parameters with its private key. The RSA key is only used to sign, so it does not weaken forward secrecy. Publicly trusted CAs issue RSA certificates with keys of at least 2048 bits.

Encryption: AES with a 256-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: GCM (Galois/Counter Mode), an AEAD: counter-mode encryption plus a GHASH authenticator with a 16-byte tag, checked in one step, so the CBC padding attacks don't apply. In TLS 1.2 the 12-byte nonce is a 4-byte implicit salt from the key block plus an 8-byte explicit part sent with every record, as first specified for AES-GCM in RFC 5288 (2008); a nonce must never repeat under the same key.

Integrity: there is no separate MAC because the AEAD tag authenticates every record. The SHA384 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_DHE_RSA_WITH_AES_256_GCM_SHA384 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 3 of the 9 libraries tracked here: NSS 3.133, Java 21 (SunJSSE) and 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_DHE_RSA_WITH_AES_256_GCM_SHA384 (0x00,0x9F) is registered in the IANA TLS Cipher Suites registry with RFC 5288, “AES Galois Counter Mode (GCM) Cipher Suites for TLS” (August 2008, Standards Track) as its specification. RFC 9325 (2022), part of BCP 195, says TLS 1.2 implementations SHOULD NOT negotiate TLS_DHE_* suites, citing the Raccoon attack and the poor uptake of negotiated groups. RFC 10015 (2026) now says clients MUST NOT offer and servers MUST NOT select FFDHE suites in (D)TLS 1.2, and IANA changed this entry's Recommended value to D.

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:DHE-RSA-AES256-GCM-SHA384';
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:DHE-RSA-AES256-GCM-SHA384
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:!DHE-RSA-AES256-GCM-SHA384';

# 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:!DHE-RSA-AES256-GCM-SHA384

How to test whether a server accepts it

Offer only TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 with openssl s_client; if the handshake completes, the server accepts it:

openssl s_client -connect example.com:443 -tls1_2 -cipher DHE-RSA-AES256-GCM-SHA384 </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_DHE_RSA_WITH_AES_256_GCM_SHA384 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.