# TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA cipher suite

> TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA (0x00,0x26): KRB5/KRB5 · DES-CBC-40 · SSL 3.0, TLS 1.0. ssl.sh rating: Insecure. OpenSSL/GnuTLS names and Nginx/Apache config.

Source: https://ssl.sh/ciphers/tls-krb5-export-with-des-cbc-40-sha/
Last updated: 2026-11-10

TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA (0x00,0x26) is a cipher suite for SSL 3.0, TLS 1.0: KRB5 key exchange, KRB5 authentication, DES-CBC-40 encryption and SHA1 message authentication. ssl.sh rates it Insecure.

| Field | Value |
|---|---|
| IANA | TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA |
| Hex code | 0x00,0x26 |
| OpenSSL | Not available in OpenSSL 3.5 |
| GnuTLS | - |
| Key exchange | KRB5 |
| Authentication | KRB5 |
| Encryption | DES-CBC-40 |
| MAC | SHA1 |
| TLS versions | SSL 3.0, TLS 1.0 |
| Rating | Insecure |
| IANA "Recommended" | D |
| References | RFC 2712, RFC 9847 |

## What each component means

A [cipher suite](https://ssl.sh/glossary/cipher-suite/) names the algorithms a client and server agree on in one handshake. TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA combines KRB5 key exchange, KRB5 authentication, DES-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](https://ssl.sh/learn/cipher-suites/).

Key exchange and authentication: Kerberos ([RFC 2712](https://www.rfc-editor.org/rfc/rfc2712)). 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: DES reduced to 40 bits of secret key, an export-grade cipher that ordinary hardware brute-forces quickly. [RFC 9325](https://www.rfc-editor.org/rfc/rfc9325) (2022) forbids any suite with less than 112 bits of security and names export-level 40- and 56-bit ciphers explicitly.

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](https://ssl.sh/glossary/beast/) (CVE-2011-3389) against TLS 1.0's predictable IVs, Lucky Thirteen (CVE-2013-0169, 2013), which times the MAC check, and [POODLE](https://ssl.sh/glossary/poodle/) (CVE-2014-3566, 2014) against SSL 3.0's unchecked padding. [RFC 9325](https://www.rfc-editor.org/rfc/rfc9325) (2022) says CBC suites SHOULD NOT be used unless the encrypt_then_mac extension ([RFC 7366](https://www.rfc-editor.org/rfc/rfc7366)) is also negotiated.

Integrity: HMAC-SHA1. [SHA-1](https://ssl.sh/glossary/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

- Export-grade cryptography (40/56-bit keys), broken since the 1990s and exploited by FREAK and Logjam.
- Uses single DES, whose 56-bit key can be brute-forced; RFC 5246 removed DES suites from TLS 1.2.

## Which TLS libraries support it

Support for TLS_KRB5_EXPORT_WITH_DES_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.

| Library | Status | Details |
|---|---|---|
| OpenSSL 3.5 | Not supported | - |
| GnuTLS | Not supported | - |
| BoringSSL | Not supported | - |
| Go crypto/tls | Not supported | - |
| NSS 3.133 | Not supported | - |
| Firefox | Not supported | - |
| Java 21 (SunJSSE) | Not supported | - |
| Windows Schannel (Windows 11 / Server 2022) | Not supported | - |
| rustls 0.23.46 | Not supported | - |

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.

- [BoringSSL — ssl/ssl_cipher.cc (main)](https://boringssl.googlesource.com/boringssl/+/refs/heads/main/ssl/ssl_cipher.cc) (2026-11-10)
- [Go — src/crypto/tls/cipher_suites.go (master)](https://github.com/golang/go/blob/master/src/crypto/tls/cipher_suites.go) (2026-11-10)
- [Go — src/crypto/tls/defaults.go (master)](https://github.com/golang/go/blob/master/src/crypto/tls/defaults.go) (2026-11-10)
- [NSS — lib/ssl/ssl3con.c (as vendored in Firefox)](https://github.com/mozilla-firefox/firefox/blob/main/security/nss/lib/ssl/ssl3con.c) (2026-11-10)
- [NSS — TAG-INFO](https://github.com/mozilla-firefox/firefox/blob/main/security/nss/TAG-INFO) (2026-11-10)
- [Firefox — security/manager/ssl/nsNSSComponent.cpp](https://github.com/mozilla-firefox/firefox/blob/main/security/manager/ssl/nsNSSComponent.cpp) (2026-11-10)
- [Firefox — modules/libpref/init/StaticPrefList.yaml](https://github.com/mozilla-firefox/firefox/blob/main/modules/libpref/init/StaticPrefList.yaml) (2026-11-10)
- [Oracle — JDK 21 Providers Documentation: SunJSSE Cipher Suites](https://docs.oracle.com/en/java/javase/21/security/oracle-providers.html#GUID-7093246A-31A3-4304-AC5F-5FB6400405E2) (2026-11-10)
- [Oracle — JDK 21 JSSE Reference Guide: jdk.tls.disabledAlgorithms](https://docs.oracle.com/en/java/javase/21/security/java-secure-socket-extension-jsse-reference-guide.html) (2026-11-10)
- [Microsoft Learn — TLS Cipher Suites in Windows 11](https://learn.microsoft.com/en-us/windows/win32/secauthn/tls-cipher-suites-in-windows-11) (2026-11-10)
- [Microsoft Learn — TLS Cipher Suites in Windows Server 2022](https://learn.microsoft.com/en-us/windows/win32/secauthn/tls-cipher-suites-in-windows-server-2022) (2026-11-10)
- [docs.rs — rustls 0.23.46 crypto::aws_lc_rs (default provider)](https://docs.rs/rustls/0.23.46/src/rustls/crypto/aws_lc_rs/mod.rs.html) (2026-11-10)

## History and standards status

TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA (0x00,0x26) is registered in the IANA TLS Cipher Suites registry with [RFC 2712](https://www.rfc-editor.org/rfc/rfc2712), “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](https://www.rfc-editor.org/rfc/rfc7568) (2015) deprecated SSL 3.0 and [RFC 8996](https://www.rfc-editor.org/rfc/rfc8996) (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](https://www.rfc-editor.org/rfc/rfc9847) (2025).

## How to test whether a server accepts it

OpenSSL 3.5 cannot offer TLS_KRB5_EXPORT_WITH_DES_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_DES_CBC_40_SHA in its output:

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

To decode a name or hex code, use the [cipher suite lookup](https://ssl.sh/tools/cipher-suite-lookup/); the [SSL checker](https://ssl.sh/tools/ssl-checker/) shows which protocol versions a live server accepts and the cipher suite it negotiates.

## FAQ

### Is TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA secure?

No. ssl.sh rates it insecure. Export-grade cryptography (40/56-bit keys), broken since the 1990s and exploited by FREAK and Logjam. It can only be negotiated in SSL 3.0, TLS 1.0. [RFC 7568](https://www.rfc-editor.org/rfc/rfc7568) (2015) deprecated SSL 3.0 and [RFC 8996](https://www.rfc-editor.org/rfc/rfc8996) (2021) deprecated TLS 1.0 and TLS 1.1, so no protocol version still in good standing allows it.

### Can TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA be used with TLS 1.3?

No. It only works with SSL 3.0, TLS 1.0, all deprecated. TLS 1.3 uses its own suites such as [TLS_AES_128_GCM_SHA256](https://ssl.sh/ciphers/tls-aes-128-gcm-sha256/).

### How do I disable TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA in Nginx or Apache?

There is nothing to disable: OpenSSL 3.5, which Nginx and Apache httpd normally use, does not implement TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA, so they cannot negotiate it.

### Which clients and libraries still support TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA?

Not supported: OpenSSL 3.5, GnuTLS, BoringSSL, Go crypto/tls, NSS 3.133, Firefox, Java 21 (SunJSSE), Windows Schannel (Windows 11 / Server 2022) and rustls 0.23.46.