TLS_SRP_SHA_WITH_AES_128_CBC_SHA

What each component means

A cipher suite names the algorithms a client and server agree on in one handshake. TLS_SRP_SHA_WITH_AES_128_CBC_SHA combines SRP key exchange, SRP authentication, AES-128-CBC encryption and SHA1 integrity protection. Each part is explained below with its known weaknesses; for the bigger picture see how cipher suites work.

Key exchange: SRP, the Secure Remote Password protocol (RFC 5054). Client and server authenticate each other with a password, but the server stores only a verifier derived from it and the password never crosses the wire, so an eavesdropper cannot run an offline dictionary attack on a recorded handshake. The SRP-RSA and SRP-DSS variants additionally sign the SRP parameters with a server certificate. RFC 5054 only defines SRP with 3DES or AES in CBC mode and HMAC-SHA1.

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: CBC with MAC-then-encrypt. TLS 1.2 and earlier compute the HMAC over the plaintext, then pad and encrypt, so a receiver has to decrypt before it can check integrity. That ordering produced a long run of padding-oracle attacks: BEAST (CVE-2011-3389) against TLS 1.0's predictable IVs, Lucky Thirteen (CVE-2013-0169, 2013), which times the MAC check, and POODLE (CVE-2014-3566, 2014) against SSL 3.0's unchecked padding. RFC 9325 (2022) says CBC suites SHOULD NOT be used unless the encrypt_then_mac extension (RFC 7366) is also negotiated.

Integrity: HMAC-SHA1. SHA-1 collisions are practical (SHAttered, 2017), but HMAC does not rely on collision resistance, so HMAC-SHA1 record MACs are not considered broken; this suite's weak points lie elsewhere. When TLS 1.2 is negotiated, keys are derived with the SHA-256 PRF, which RFC 5246 (2008) applies to every cipher suite defined before it.

Why this rating

ssl.sh rating: Weak. The reasons:

• CBC mode with a separate MAC (MAC-then-encrypt), the construction behind padding-oracle attacks such as Lucky Thirteen; prefer an AEAD cipher.

How ssl.sh rates cipher suites

Which TLS libraries support it

Support for TLS_SRP_SHA_WITH_AES_128_CBC_SHA 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_SRP_SHA_WITH_AES_128_CBC_SHA (0xC0,0x1D) is registered in the IANA TLS Cipher Suites registry with RFC 5054, “Using the Secure Remote Password (SRP) Protocol for TLS Authentication” (November 2007, Informational) as its specification. RFC 9325 (2022), part of BCP 195, says CBC suites SHOULD NOT be used unless encrypt_then_mac is negotiated. 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:!SRP-AES-128-CBC-SHA';

# 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:!SRP-AES-128-CBC-SHA

How to test whether a server accepts it

Offer only TLS_SRP_SHA_WITH_AES_128_CBC_SHA with openssl s_client; if the handshake completes, the server accepts it:

openssl s_client -connect example.com:443 -tls1_2 -cipher SRP-AES-128-CBC-SHA </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_SRP_SHA_WITH_AES_128_CBC_SHA 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.