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修复ssh的rsa身份认证

tree by Bessi
ssh-rsa身份认证失败”no matching host key type found. Their offer: ssh-rsa”

某日,我笔记本的Debian进行了大版本升级,然后当我尝试ssh到服务器时提示我身份认证失败,错误信息为:
no matching host key type found. Their offer: ssh-rsa

原来,从openssh 8.8开始,默认禁用了使用SHA-1算法的RSA密钥。

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OpenSSH 8.8 was released on 2021-09-26. It is available from the
mirrors listed at https://www.openssh.com/.

...
...

Potentially-incompatible changes
================================

This release disables RSA signatures using the SHA-1 hash algorithm
by default. This change has been made as the SHA-1 hash algorithm is
cryptographically broken, and it is possible to create chosen-prefix
hash collisions for <USD$50K [1]

上文大意为因为SHA-1希哈算法可以被爆力破解了,所以自此版本(8.8)开始默认禁用使用了SHA-1算法的RSA密钥。

重新启用ssh-RSA认证

如果服务器端的SSH只支持ssh-RSA认证,那么我们只能重新启用它。

openssh 8.8的README中,给出了重新启用RSA密钥的方法,如下:

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Host haven200
HostName haven200.com
HostKeyAlgorithms=+ssh-rsa
PubkeyAcceptedKeyTypes=+ssh-rsa
User haven200
Port 22
Protocol 2
SendEnv upnpcv
IdentityFile ~/.ssh/haven200_rsa

即使用HostKeyAlgorithms=+ssh-rsaPubkeyAcceptedKeyTypes=+ssh-rsa来重新启用RSA密钥。

升级SSH认证

为了安全,我们使用更安全的ecdsa密钥来替代RSA密钥进行身份认证。

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~$ ssh-keygen -t ecdsa -f ~/.ssh/haven200_ecdsa

References:
openssh

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