TLS_AES_128_GCM_ASCONHASH256

What each component means

A cipher suite names the algorithms a client and server agree on in one handshake. TLS_AES_128_GCM_ASCONHASH256 combines the AES-128-GCM AEAD with the ASCONHASH256 hash. Each part is explained below with its known weaknesses; for the bigger picture see how cipher suites work.

TLS 1.3 suites only describe the symmetric part. The TLS 1.3 specification (RFC 9846) says its suites specify only the symmetric ciphers and cannot be used with TLS 1.2. Key exchange is negotiated separately through the supported_groups and key_share extensions (for example X25519, P-256 or the hybrid X25519MLKEM768) and is always ephemeral (EC)DHE unless a client resumes in the PSK-only psk_ke mode, so a full handshake always has forward secrecy. The certificate signature algorithm (for example RSA-PSS, ECDSA or Ed25519) is negotiated with signature_algorithms. In TLS_AES_128_GCM_ASCONHASH256, ASCONHASH256 is the hash behind the HKDF key schedule and the handshake transcript hash.

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: GCM (Galois/Counter Mode), an AEAD: counter-mode encryption plus a GHASH authenticator with a 16-byte tag, checked in one step. In TLS 1.3 the nonce is the record sequence number XORed with a per-direction IV, so nothing extra travels with each record and nonces cannot repeat.

Why this rating

ssl.sh rating: Secure. The reasons:

• A TLS 1.3 AEAD suite, but IANA doesn't mark it "Recommended" (truncated tag, national or experimental algorithm, or limited client support).

How ssl.sh rates cipher suites

Which TLS libraries support it

Support for TLS_AES_128_GCM_ASCONHASH256 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. None of them implements it.

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_AES_128_GCM_ASCONHASH256 (0x00,0x70) is registered in the IANA TLS Cipher Suites registry with RFC 9846, “The Transport Layer Security (TLS) Protocol Version 1.3” (July 2026, Standards Track) as its specification. The algorithm itself is standardised in NIST SP 800-232. TLS 1.3 was first published as RFC 8446 (2018) and republished as RFC 9846 (2026), which obsoletes RFC 8446. 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

OpenSSL 3.5 doesn't implement this suite, so stock Nginx and Apache httpd builds can't offer it and you don't need to disable it.

How to test whether a server accepts it

OpenSSL 3.5 cannot offer TLS_AES_128_GCM_ASCONHASH256, so openssl s_client can't test it directly; use a scanner that implements the suite itself.

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_AES_128_GCM_ASCONHASH256 in its output:

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

If your nmap build doesn't print a TLS 1.3 section, rely on the openssl command instead.

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.