TLS_KRB5_WITH_DES_CBC_MD5

What each component means

A cipher suite names the algorithms a client and server agree on in one handshake. TLS_KRB5_WITH_DES_CBC_MD5 combines KRB5 key exchange, KRB5 authentication, DES-CBC encryption and MD5 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.

Encryption: single DES with a 56-bit key. The EFF's Deep Crack machine recovered a DES key by brute force in 56 hours in 1998, so this encryption offers no real protection today. RFC 5246 (2008) removed the DES suites from TLS 1.2.

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-MD5. MD5 collisions have been practical since 2004; HMAC-MD5 is not directly broken, but MD5 survives only in suites whose ciphers are already obsolete, and RFC 9155 (2021) has since removed MD5 from TLS 1.2 signatures too.

Why this rating

ssl.sh rating: Insecure. The reasons:

• Uses single DES, whose 56-bit key can be brute-forced; RFC 5246 removed DES suites from TLS 1.2.
• Uses HMAC-MD5 for integrity; MD5 is broken and these suites are deprecated.

How ssl.sh rates cipher suites

Which TLS libraries support it

Support for TLS_KRB5_WITH_DES_CBC_MD5 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_WITH_DES_CBC_MD5 (0x00,0x22) 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. The TLS 1.2 specification, RFC 5246 (2008), removed the IDEA and DES suites, calling them deprecated. It can only be negotiated in TLS 1.0, TLS 1.1. 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_WITH_DES_CBC_MD5, 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_WITH_DES_CBC_MD5 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.