TLS_KRB5_EXPORT_WITH_RC2_CBC_40_SHA

What each component means

A cipher suite names the algorithms a client and server agree on in one handshake. TLS_KRB5_EXPORT_WITH_RC2_CBC_40_SHA combines KRB5 key exchange, KRB5 authentication, RC2-CBC-40 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 and authentication: Kerberos (RFC 2712). Instead of a certificate exchange, the client presents a Kerberos service ticket and the premaster secret is protected with the ticket's session key, so TLS can reuse existing Kerberos infrastructure. These suites were only ever defined with DES, 3DES, RC4, IDEA and 40-bit export ciphers, so no modern combination exists, and OpenSSL 3.5 implements none of them.

This is a 1990s EXPORT suite: the bulk cipher is limited to 40 bits of secret key to satisfy US export rules of the time, which ordinary hardware can brute-force today.

Encryption: RC2 in CBC mode with a 40-bit effective key, an export-grade cipher that ordinary hardware brute-forces quickly. RFC 9325 (2022) forbids any suite with less than 112 bits of security.

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.

Why this rating

ssl.sh rating: Insecure. The reasons:

• Export-grade cryptography (40/56-bit keys), broken since the 1990s and exploited by FREAK and Logjam.
• Uses RC2 with a 40-bit export key.

How ssl.sh rates cipher suites

Which TLS libraries support it

Support for TLS_KRB5_EXPORT_WITH_RC2_CBC_40_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. 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_KRB5_EXPORT_WITH_RC2_CBC_40_SHA (0x00,0x27) is registered in the IANA TLS Cipher Suites registry with RFC 2712, “Addition of Kerberos Cipher Suites to Transport Layer Security (TLS)” (October 1999, Standards Track) as its specification. It can only be negotiated in SSL 3.0, TLS 1.0. RFC 7568 (2015) deprecated SSL 3.0 and RFC 8996 (2021) deprecated TLS 1.0 and TLS 1.1, so no protocol version still in good standing allows it. The registry marks it D (discouraged), a value introduced by RFC 9847 (2025).

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_KRB5_EXPORT_WITH_RC2_CBC_40_SHA, 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_KRB5_EXPORT_WITH_RC2_CBC_40_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.