[Kerberos] User Ticket Management

Kerberos客户端常用命令包括 kinitklistkdestroy, 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 jennifer@ATHENA.MIT.EDU: <-- [Type jennifer's password here.]
shell%

如果想要申请 forwardable ticket,可以

shell% kinit -f
Password for jennifer@ATHENA.MIT.EDU: <-- [Type your password here.]
shell%
shell% kinit -f -l 3h david@EXAMPLE.COM
Password for david@EXAMPLE.COM: <-- [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: jennifer@ATHENA.MIT.EDU Valid starting Expires Service principal
// :: // :: krbtgt/ATHENA.MIT.EDU@ATHENA.MIT.EDU
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: jennifer@ATHENA.MIT.EDU Valid starting Expires Service principal
// :: // :: krbtgt/ATHENA.MIT.EDU@ATHENA.MIT.EDU
// :: // :: host/daffodil.mit.edu@ATHENA.MIT.EDU
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
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