From: Ben Kaduk Date: Fri, 31 May 2013 16:40:10 +0000 (-0400) Subject: Clarify retiring-des based on user feedback X-Git-Tag: krb5-1.12-alpha1~140 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=fa6de1bf73926751a2f68bff31ef020eb7db9260;p=thirdparty%2Fkrb5.git Clarify retiring-des based on user feedback Explain why DES keys should be removed from principals, and clarify that allow_weak_crypto overrides all other configuration. ticket: 7654 (new) tags: pullup target_version: 1.11.4 --- diff --git a/doc/admin/advanced/retiring-des.rst b/doc/admin/advanced/retiring-des.rst index da9d1fcf7a..cbca1b7983 100644 --- a/doc/admin/advanced/retiring-des.rst +++ b/doc/admin/advanced/retiring-des.rst @@ -298,6 +298,19 @@ as new DES keys are still being generated, and will be used if requested by a client. To make more progress removing DES from the realm, the KDC should be configured to not generate such keys by default. +.. note:: + + An attacker posing as a client can implement a brute force attack against + a DES key for any principal, if that key is in the current (highest-kvno) + key list. This attack is only possible if **allow_weak_crypto = true** + is enabled on the KDC. Setting the **+requires_preauth** flag on a + principal forces this attack to be an online attack, much slower than + the offline attack otherwise available to the attacker. However, setting + this flag on a service principal is not always advisable; see the entry in + :ref:`add_principal` for details. + +The following KDC configuration will not generate DES keys by default: + :: [realms] @@ -357,8 +370,11 @@ generate DES keys by default. Entry for principal kaduk@ZONE.MIT.EDU with kvno 3, encryption type des3-cbc-sha1 added to keytab WRFILE:kaduk-zone.keytab. Once all principals have been re-keyed, DES support can be disabled on the -KDC, and client machines can remove **allow_weak_crypto = true** from -their :ref:`krb5.conf(5)` configuration files, completing the migration. +KDC (**allow_weak_crypto = false**), and client machines can remove +**allow_weak_crypto = true** from their :ref:`krb5.conf(5)` configuration +files, completing the migration. **allow_weak_crypto** takes precedence over +all places where DES enctypes could be explicitly configured. DES keys will +not be used, even if they are present, when **allow_weak_crypto = false**. Support for legacy services ~~~~~~~~~~~~~~~~~~~~~~~~~~~