On 3/7/22 18:29, Brian Candler wrote:
On 07/03/2022 16:38, Michael Ströder wrote:
libpam-google-auth and other similar PAM modules require to store the
token's shared secrets on the server. If your system gets hacked and
shared secrets are stolen the attacker can generate an arbitrary
amount of valid OTP values. And if you use the same shared secrets on
multiple servers the security impact will be broad.
=> Don't use that.
That's a nice thing about pam_yubico with real Yubikeys: they can be
validated against the Yubico cloud API, without any local secrets.
1. I'd never want to use tokens pre-provisioned tokens with admins'
shared secrets stored in the cloud and reach out to it via Internet from
every internal server.
Shameless plug: I'm using my own OATH-LDAP with shared secrets stored
encrypted in OpenLDAP, but not for SSH (see 3.).
2. Consider availability issues: In case of urgent admin SSH access your
infrastructure might be (partially) broken and Yubico's cloud unreachable.
3. Furthermore any OTP mechanism is not really usable when using tools
like ansible or similar in mass deployments.
BTW: Using keys on hardware tokens including U2F/Fido is also too slow
if you initially connect to thousands of machines.
=> Use an SSH-CA which issues short-term user certs.
Ciao, Michael.
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