Kerberos: The Network Authentication Protocol

https://web.mit.edu/kerberos/
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What is Kerberos?
Announcements
    Security Advisories
    Kerberos Version 4 End of Life Announcement 
Kerberos Releases
    Current release: krb5-1.15.2
    Maintenance release: krb5-1.14.6
    Kerberos for Windows: kfw-4.1
    Historical releases of MIT krb5 
Download
    Sources and binaries from MIT 
Releases in testing
    The krb5-current Snapshots (for developers only) 
Documentation
    Documentation for the latest release
    Documentation for unreleased development code
    How do the new US export regulations affect Kerberos?
    Papers about the Kerberos protocol
    Kerberos Y2K statement 
The MIT Kerberos Team
Contact Information
The MIT Kerberos Consortium
Other Resources
    Mailing lists
    comp.protocols.kerberos newsgroup
    USC/ISI Kerberos Page
    Oak Ridge National Laboratory's "How to Kerberize your Site" 

Recent News

Old news is archived.
25 Sep 2017 - krb5-1.15.2 is released

The krb5-1.15.2 source release is now available.
25 Sep 2017 - krb5-1.14.6 is released

The krb5-1.14.6 source release is now available.
What is Kerberos?

Kerberos is a network authentication protocol. It is designed to provide strong authentication for client/server applications by using secret-key cryptography. A free implementation of this protocol is available from the Massachusetts Institute of Technology. Kerberos is available in many commercial products as well.

The Internet is an insecure place. Many of the protocols used in the Internet do not provide any security. Tools to “sniff” passwords off of the network are in common use by malicious hackers. Thus, applications which send an unencrypted password over the network are extremely vulnerable. Worse yet, other client/server applications rely on the client program to be “honest” about the identity of the user who is using it. Other applications rely on the client to restrict its activities to those which it is allowed to do, with no other enforcement by the server.

Some sites attempt to use firewalls to solve their network security problems. Unfortunately, firewalls assume that “the bad guys” are on the outside, which is often a very bad assumption. Most of the really damaging incidents of computer crime are carried out by insiders. Firewalls also have a significant disadvantage in that they restrict how your users can use the Internet. (After all, firewalls are simply a less extreme example of the dictum that there is nothing more secure than a computer which is not connected to the network — and powered off!) In many places, these restrictions are simply unrealistic and unacceptable.

Kerberos was created by MIT as a solution to these network security problems. The Kerberos protocol uses strong cryptography so that a client can prove its identity to a server (and vice versa) across an insecure network connection. After a client and server has used Kerberos to prove their identity, they can also encrypt all of their communications to assure privacy and data integrity as they go about their business.

Kerberos is freely available from MIT, under copyright permissions very similar those used for the BSD operating system and the X Window System. MIT provides Kerberos in source form so that anyone who wishes to use it may look over the code for themselves and assure themselves that the code is trustworthy. In addition, for those who prefer to rely on a professionally supported product, Kerberos is available as a product from many different vendors.

In summary, Kerberos is a solution to your network security problems. It provides the tools of authentication and strong cryptography over the network to help you secure your information systems across your entire enterprise. We hope you find Kerberos as useful as it has been to us. At MIT, Kerberos has been invaluable to our Information/Technology architecture.

$Id: index.html,v 1.237 2017/09/25 17:33:35 ghudson Exp $

All images and text on this page are copyright MIT.

MIT Kerberos [ home ] [ contact ]

### 关于 `su: Authentication failure` 错误的原因及解决方法 当遇到 `su: Authentication failure` 的错误时,这通常意味着尝试切换用户身份失败。此问题可能由多种因素引起。 #### 可能原因分析 1. **密码输入错误** 如果提供的密码不正确,则会触发认证失败的信息。确保输入的是目标用户的正确密码[^1]。 2. **PAM配置文件损坏或设置不当** PAM(Pluggable Authentication Modules)用于管理各种认证方式。如果 `/etc/pam.d/su` 文件被修改过或者存在语法错误,可能会阻止正常的认证过程。 3. **账户锁定状态** 用户账号可能因为多次登录失败而自动锁定了。可以查看 `/var/log/secure` 或者通过命令 `lastb` 来确认是否有连续的失败记录,并检查是否达到了系统的锁定阈值。 4. **SELinux策略冲突** SELinux的安全上下文可能导致某些操作受限。可以通过临时关闭 SELinux (`setenforce 0`) 测试是否与此有关联;如果是的话,需调整相应的安全标签以允许正常工作。 5. **环境变量影响** 特定环境下定义的一些环境变量也可能干扰到 su 命令的行为。例如 PATH 中包含了恶意路径或者其他潜在风险的因素都应予以排查。 6. **shadow文件权限不足** 若 `/etc/shadow` 文件的读取权限不对,也会造成认证流程中断。该文件应当只可由 root 访问,其他任何更改都会引发安全隐患以及功能障碍。 7. **TTY设备限制** 对于远程连接来说,可能存在 TTY 设备上的访问控制列表ACL(Access Control List),它规定了哪些终端能够执行特定指令。比如,在 SSH 远程登录的情况下,需要保证所使用的伪TTY属于许可范围内。 8. **系统时间不同步** 时间戳验证机制下,服务器之间的时间差异过大同样会影响基于 Kerberos 等协议的身份验证成功与否。保持 NTP(Network Time Protocol) 客户端同步是非常重要的预防措施之一。 9. **硬件令牌或其他双因子认证组件失效** 当启用了额外层次的安全保护之后,丢失或失灵的相关配件自然会造成无法完成整个鉴权环节。 #### 解决方案建议 针对上述提到的各种可能性,采取如下对应措施: - 验证并重新输入正确的用户名和密码组合。 - 复原默认版本的 PAM 配置文件至原始状态,即恢复成发行版自带的内容。 - 使用 `passwd` 工具重设受影响帐户的新密码来解锁它们。 - 调整 SELinux 设置为宽容模式(permissive mode),观察现象变化后再做进一步优化。 - 清理不必要的环境变量设定,特别是那些来自不受信任源的部分。 - 修改 shadow 数据库对象属性使其符合标准要求(`chmod 600 /etc/shadow`)。 - 编辑 sudoers 文档加入必要的 tty 白名单项(如 Defaults:%wheel !requiretty )。 - 同步本地机器与外部权威授时中心之间的日期时间和时区参数。 - 更换已坏掉或是遗失的重要物理介质,同时更新软件内登记信息以便继续正常使用多级防护体系下的资源访问请求处理逻辑。 ```bash # 检查当前selinux状态 getenforce # 将selinux暂时改为permissive模式 sudo setenforce 0 # 查看最近一次登陆情况 lastlog | grep username # 显示最后一次失败尝试详情 lastb -n 1 ```
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