[Kerberos] User Ticket Management

Kerberos客户端常用命令包括 kinit, klist, kdestroy, and kpasswd，用户使用这些命令管理自己的 ticket。

此外，每台运行Kerberos的机器应该都配置/etc/krb5.conf，At a minimum, it should define a default_realm setting in [libdefaults]. If you are not using DNS SRV records, it must also contain a [realms] section containing information for your realm’s KDCs.

Ticket 管理

Kerberos Ticket的若干属性：

• forwardable 简单来讲，KDC可以基于该类型TGT发放新的TGT，即使 network address不同。这样不需要再次输入密码。
• proxiable 类似于forwardable，但是不同的是只允许service继承client的认证
• proxy 
• postdated 
• Renewable 用户不需要重新输入密码就可以获得新的 session key. 但是这种TGT有过期时间。
• invalid 
• hardware authentication 申请使用硬件的Ticket认证
• okay as delegate ticket指定的服务器可以用作delegate determined by the policy of that realm
• anonymous ticket is one in which the named principal is a generic principal for that realm; it does not actually specify the individual that will be using the ticket. This ticket is meant only to securely distribute a session key.

用 kinit 获得Ticket

如果你的登录系统集成了Kerberos v5，那么登录时自动获得kerberos ticket. 否则，必须显示获取，比如用 kinit。类似，如果 ticket过期了，kinit可以申请新的ticket. 

By default, kinit假设你想要默认realm里与自己名字相同的principal的ticket。

shell% kinit
Password for [email protected]: <-- [Type jennifer's password here.]
shell%

如果想要申请 forwardable ticket，可以

shell% kinit -f
Password for [email protected]: <-- [Type your password here.]
shell%
shell% kinit -f -l 3h [email protected]
Password for [email protected]: <-- [Type david's password here.]
shell%

用 klist 查看 ticket

当你第一次获得 ticket, 那么只能是TGT，看起来如下：

shell% klist
Ticket cache: /tmp/krb5cc_ttypa
Default principal: [email protected]

Valid starting     Expires            Service principal
06/07/04 19:49:21  06/08/04 05:49:19  krbtgt/[email protected]
shell%

如果连接到其他机器上，比如：daffodil.mit.edu，但是在同一个realm，klist会得到

shell% klist
Ticket cache: /tmp/krb5cc_ttypa
Default principal: [email protected]

Valid starting     Expires            Service principal
06/07/04 19:49:21  06/08/04 05:49:19  krbtgt/[email protected]
06/07/04 20:22:30  06/08/04 05:49:19  host/[email protected]
shell%

当jennifer用ssh程序登陆主机daffodil.mit.edu，ssh程序将jennifer的TGT给KDC，并请求主机ticket，这样jennifer不用再输入密码。

klist有各种flag，具体可以通过 man klist 查看。

用 kdestory 销毁ticket. 

由于ticket可能被偷走，这样离开机器的时候可以顺便销毁ticket.

shell% kdestroy
shell%

其他客户端命令

• kdestroy: kdestroy utility destroys the user’s active Kerberos authorization tickets by overwriting and deleting the credentials cache that contains them
• kinit: kinit obtains and caches an initial ticket-granting ticket(TGT) for principal
• klist: klist lists the Kerberos principal and Kerberos tickets held in a credentials cache, or the keys held in a keytab file.
• kpasswd: kpasswd command is used to change a Kerberos principal’s password
• krb5-config
• ksu
• kswitch
• kvno
• sclient