Restrict SSH CA certificates to specific users/groups

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Is it possible to restrict the use of CA certificates to specific users/principals/groups?



The use case is that I'd like to have 2 CA certificates. One would be used as part of an automated system to sign user keys. If this certificate were to be compromised, I want to be sure that it couldn't be used to allow someone to log into an admin account.



The other CA certificate would obviously be more securely stored (airgapped etc.) and used for admin accounts.




ssh openssh certificates




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  • Just so I understand: you want to make sure that if CA1 erroneously certifies a public key for user root, it still would not work?
    – Ulrich Schwarz
    Jan 13 at 18:14






  • 1




    According to sshd docs, TrustedUserCAKeys is valid in Match sections, so I think that Match User root should work?
    – Ulrich Schwarz
    Jan 13 at 18:18















up vote
0
down vote

favorite












Is it possible to restrict the use of CA certificates to specific users/principals/groups?



The use case is that I'd like to have 2 CA certificates. One would be used as part of an automated system to sign user keys. If this certificate were to be compromised, I want to be sure that it couldn't be used to allow someone to log into an admin account.



The other CA certificate would obviously be more securely stored (airgapped etc.) and used for admin accounts.




ssh openssh certificates




share|improve this question




















  • Just so I understand: you want to make sure that if CA1 erroneously certifies a public key for user root, it still would not work?
    – Ulrich Schwarz
    Jan 13 at 18:14






  • 1




    According to sshd docs, TrustedUserCAKeys is valid in Match sections, so I think that Match User root should work?
    – Ulrich Schwarz
    Jan 13 at 18:18













up vote
0
down vote

favorite









up vote
0
down vote

favorite











Is it possible to restrict the use of CA certificates to specific users/principals/groups?



The use case is that I'd like to have 2 CA certificates. One would be used as part of an automated system to sign user keys. If this certificate were to be compromised, I want to be sure that it couldn't be used to allow someone to log into an admin account.



The other CA certificate would obviously be more securely stored (airgapped etc.) and used for admin accounts.




ssh openssh certificates




share|improve this question












Is it possible to restrict the use of CA certificates to specific users/principals/groups?



The use case is that I'd like to have 2 CA certificates. One would be used as part of an automated system to sign user keys. If this certificate were to be compromised, I want to be sure that it couldn't be used to allow someone to log into an admin account.



The other CA certificate would obviously be more securely stored (airgapped etc.) and used for admin accounts.





ssh openssh certificates





share|improve this question











share|improve this question




share|improve this question










asked Jan 13 at 16:26









Sam Bull

1053




1053











  • Just so I understand: you want to make sure that if CA1 erroneously certifies a public key for user root, it still would not work?
    – Ulrich Schwarz
    Jan 13 at 18:14






  • 1




    According to sshd docs, TrustedUserCAKeys is valid in Match sections, so I think that Match User root should work?
    – Ulrich Schwarz
    Jan 13 at 18:18

















  • Just so I understand: you want to make sure that if CA1 erroneously certifies a public key for user root, it still would not work?
    – Ulrich Schwarz
    Jan 13 at 18:14






  • 1




    According to sshd docs, TrustedUserCAKeys is valid in Match sections, so I think that Match User root should work?
    – Ulrich Schwarz
    Jan 13 at 18:18
















Just so I understand: you want to make sure that if CA1 erroneously certifies a public key for user root, it still would not work?
– Ulrich Schwarz
Jan 13 at 18:14




Just so I understand: you want to make sure that if CA1 erroneously certifies a public key for user root, it still would not work?
– Ulrich Schwarz
Jan 13 at 18:14




1




1




According to sshd docs, TrustedUserCAKeys is valid in Match sections, so I think that Match User root should work?
– Ulrich Schwarz
Jan 13 at 18:18





According to sshd docs, TrustedUserCAKeys is valid in Match sections, so I think that Match User root should work?
– Ulrich Schwarz
Jan 13 at 18:18











1 Answer
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Based on Ulrich Schwarz's comment:



If I add normal users to an endusers group, then I can set the sshd_config like this:



TrustedUserCAKeys /etc/ssh/admin_ca.pub
Match Group endusers
 TrustedUserCAKeys /etc/ssh/user_ca.pub


This results in the user_ca only being accepted for users in the endusers group, while the admin_ca can be used for any user.






share|improve this answer






















  • But you do not have to match the normal users for the protection you asked for but the admin accounts.
    – Hauke Laging
    Jan 14 at 15:53










  • Both works. But, I'd rather restrict the less secure CA to a specific group of restricted users. That way I can be certain that this CA will never be used to log into any other account that may have less restrictions (admin or otherwise).
    – Sam Bull
    Jan 14 at 20:38










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1 Answer
1






active

oldest

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1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes








up vote
0
down vote



accepted










Based on Ulrich Schwarz's comment:



If I add normal users to an endusers group, then I can set the sshd_config like this:



TrustedUserCAKeys /etc/ssh/admin_ca.pub
Match Group endusers
 TrustedUserCAKeys /etc/ssh/user_ca.pub


This results in the user_ca only being accepted for users in the endusers group, while the admin_ca can be used for any user.






share|improve this answer






















  • But you do not have to match the normal users for the protection you asked for but the admin accounts.
    – Hauke Laging
    Jan 14 at 15:53










  • Both works. But, I'd rather restrict the less secure CA to a specific group of restricted users. That way I can be certain that this CA will never be used to log into any other account that may have less restrictions (admin or otherwise).
    – Sam Bull
    Jan 14 at 20:38














up vote
0
down vote



accepted










Based on Ulrich Schwarz's comment:



If I add normal users to an endusers group, then I can set the sshd_config like this:



TrustedUserCAKeys /etc/ssh/admin_ca.pub
Match Group endusers
 TrustedUserCAKeys /etc/ssh/user_ca.pub


This results in the user_ca only being accepted for users in the endusers group, while the admin_ca can be used for any user.






share|improve this answer






















  • But you do not have to match the normal users for the protection you asked for but the admin accounts.
    – Hauke Laging
    Jan 14 at 15:53










  • Both works. But, I'd rather restrict the less secure CA to a specific group of restricted users. That way I can be certain that this CA will never be used to log into any other account that may have less restrictions (admin or otherwise).
    – Sam Bull
    Jan 14 at 20:38












up vote
0
down vote



accepted







up vote
0
down vote



accepted






Based on Ulrich Schwarz's comment:



If I add normal users to an endusers group, then I can set the sshd_config like this:



TrustedUserCAKeys /etc/ssh/admin_ca.pub
Match Group endusers
 TrustedUserCAKeys /etc/ssh/user_ca.pub


This results in the user_ca only being accepted for users in the endusers group, while the admin_ca can be used for any user.






share|improve this answer














Based on Ulrich Schwarz's comment:



If I add normal users to an endusers group, then I can set the sshd_config like this:



TrustedUserCAKeys /etc/ssh/admin_ca.pub
Match Group endusers
 TrustedUserCAKeys /etc/ssh/user_ca.pub


This results in the user_ca only being accepted for users in the endusers group, while the admin_ca can be used for any user.







share|improve this answer














share|improve this answer



share|improve this answer








edited Jan 14 at 14:01

























answered Jan 14 at 13:53









Sam Bull

1053




1053











  • But you do not have to match the normal users for the protection you asked for but the admin accounts.
    – Hauke Laging
    Jan 14 at 15:53










  • Both works. But, I'd rather restrict the less secure CA to a specific group of restricted users. That way I can be certain that this CA will never be used to log into any other account that may have less restrictions (admin or otherwise).
    – Sam Bull
    Jan 14 at 20:38
















  • But you do not have to match the normal users for the protection you asked for but the admin accounts.
    – Hauke Laging
    Jan 14 at 15:53










  • Both works. But, I'd rather restrict the less secure CA to a specific group of restricted users. That way I can be certain that this CA will never be used to log into any other account that may have less restrictions (admin or otherwise).
    – Sam Bull
    Jan 14 at 20:38















But you do not have to match the normal users for the protection you asked for but the admin accounts.
– Hauke Laging
Jan 14 at 15:53




But you do not have to match the normal users for the protection you asked for but the admin accounts.
– Hauke Laging
Jan 14 at 15:53












Both works. But, I'd rather restrict the less secure CA to a specific group of restricted users. That way I can be certain that this CA will never be used to log into any other account that may have less restrictions (admin or otherwise).
– Sam Bull
Jan 14 at 20:38




Both works. But, I'd rather restrict the less secure CA to a specific group of restricted users. That way I can be certain that this CA will never be used to log into any other account that may have less restrictions (admin or otherwise).
– Sam Bull
Jan 14 at 20:38












 

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