Bug 3204

Summary:	Enable user-relative revoked keys files
Product:	Portable OpenSSH	Reporter:	Jordan Macdonald <macdjord>
Component:	sshd	Assignee:	Assigned to nobody <unassigned-bugs>
Status:	NEW ---
Severity:	enhancement	CC:	macdjord
Priority:	P5
Version:	8.1p1
Hardware:	All
OS:	All
See Also:	https://bugzilla.mindrot.org/show_bug.cgi?id=2328

Description Jordan Macdonald 2020-08-29 09:33:40 AEST

The `AuthorizedKeysFile` directive supports the %h, %U, and %u tokens, but the `RevokedKeys` directive does not. Thus it is possible to grant individual users the ability to add authorized login keys (and indeed this is the default with `.ssh/authorized_keys`), including authorized certificate authorities using the `cert-authority` option, but there is no way to grant them the ability to manage their own lists of revoked keys.

This should be fixed by enabling support for the %h, %U, and %u tokens for the `RevokedKeys` directive.

See also: https://bugzilla.mindrot.org/show_bug.cgi?id=2328 , which proposes a more powerful but more complicated solution to this issue: allowing `authorized_keys` to specify a revocation list file for each certificate authority key it defines.

Comment 1 Jordan Macdonald 2020-08-29 09:53:21 AEST

Note: Both approaches - this one and the one suggested in https://bugzilla.mindrot.org/show_bug.cgi?id=2328 - offer distinct advantages:
* Maintaining separate KRLs for each certificate authority is best-practice and enables fine-grained control (e.g. revoking the signature of a particular key by a particular CA but still allowing that same key to be used if it is also signed by a different authorized CA)
* However, not everyone follows best practices, and many users will just want to have one file to append their old/invalid/compromised keys to without having to specify `crl-file="~/.ssh/revoked_keys"` separately for every CA in `authorized_keys`

Either option would satisfactorily solve the issue of allowing users to control their own revocations, but the ideal solution would probably be to offer both.


Also, if per-user revocation files are supported, it would probably be a good idea to give `RevokedKeys` a suitable default; I suggest `.ssh/revoked_keys`. It seems unwise to enable user-specified CAs by default without offering user-specified revocation.