SSH 双因素身份验证 (2FA) 与 yubikey

Question

所以我有这个漂亮的小 yubikey，我想在验证 ssh 会话时添加一个额外的安全层。在服务器端，我已经禁用了密码验证，并且只允许在登录时使用 ssh 密钥。

问题是，在为 yubikey auth 配置 sshd 和 PAM 之后，sshd 仍然只需要一个 ssh 密钥，我从未被要求提供来自 yubikey 的响应。

我如何同时需要ssh 密钥和yubikey？

(ubuntu 14.04 - trusty)

/etc/pam.d/common-auth：

auth    required    pam_yubico.so mode=client try_first_pass id=<id> key=<secret>
auth    [success=1 default=ignore]  pam_unix.so nullok_secure try_first_pass
# here's the fallback if no module succeeds
auth    requisite           pam_deny.so
# prime the stack with a positive return value if there isn't one already;
# this avoids us returning an error just because nothing sets a success code
# since the modules above will each just jump around
auth    required            pam_permit.so
# and here are more per-package modules (the "Additional" block)
auth    optional            pam_cap.so
# end of pam-auth-update config

/etc/ssh/sshd_config：

...

PasswordAuthentication no
ChallengeResponseAuthentication yes
UsePAM yes

Answer 1

好的，我坚持了下来，我想我已经想出了一个合理的解决方案。我以前缺少的主要内容是 sshd 的AuthenticationMethods publickey,password. 这强制要求同时提供公钥和密码——“密码”现在由PAM->auth-yubi. 还需要进行其他更改，请参见下文：

（Ubuntu 14.04 - 值得信赖）：

/etc/pam.d/yubi-auth

auth    required pam_yubico.so mode=client try_first_pass id=<id> key=<key>

注意：您可以在此处获取您的访问 ID 和密钥

/etc/pam.d/sshd

# Standard Un*x authentication.
#@include common-auth

# Yubikey auth
@include yubi-auth

/etc/ssh/sshd_config

UsePAM yes
ChallengeResponseAuthentication no
AuthenticationMethods publickey,password
PasswordAuthentication yes

service ssh restart

确认

从没有公钥的远程主机进行SSH

root@0a6442bcb21c:/# ssh ben@192.168.1.20
The authenticity of host '192.168.1.20 (192.168.1.20)' can't be established.
ECDSA key fingerprint is ea:2a:e3:98:35:72:66:b1:e0:65:6b:3f:60:8a:af:ab.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.1.20' (ECDSA) to the list of known hosts.
Permission denied (publickey).

使用公钥从远程主机进行SSH

$ ssh ben@192.168.1.20
Authenticated with partial success.
ben@192.168.1.20's password:
Welcome to Ubuntu 14.04.3 LTS (GNU/Linux 3.19.0-33-generic x86_64)

改进

很高兴在验证时从远程 ssh 服务器看到“Yubikey Auth:”而不是“password:”。

当ssh服务器无法联系yubico的auth验证系统时会发生什么？理想的解决方案是完全独立的。

意见和建议表示赞赏。