The document provides an overview of FIDO authentication including: 1. How FIDO authentication works by using an authenticator to verify the user and perform the authentication without revealing identity attributes. 2. The FIDO ecosystem involves authenticators, clients, servers, and metadata to understand authenticator security characteristics. 3. FIDO supports a range of authenticators from platform-based to roaming and different user verification methods while keeping user verification data private.

1. 1
TECHNICAL PRINCIPLES OF
FIDO AUTHENTICATION
Rolf Lindemann, Nok Nok Labs
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2. 2
HOW SECURE IS AUTHENTICATION?
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HOW SECURE IS AUTHENTICATION?
Attacks require physical action → not scalable
Things are never 100% secure, so focus on adequate security.
Focus on the scalable attacks first.
Scalable Attacks

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CLOUD AUTHENTICATION
DeviceSomething Authentication
Risk Analytics
Internet

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HOW DOES FIDO WORK?

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HOW DOES FIDO WORK?
DeviceUser verification FIDO Authentication
Authenticator

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HOW DOES FIDO WORK?
AuthenticatorUser verification FIDO Authentication
Require user gesture before
private key can be used
Challenge
(Signed) Response
Private key
dedicated to one
app Public key

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FIDO ECOSYSTEM
AuthenticatorUser verification FIDO Authentication
… …SE

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FIDO ECOSYSTEM
AuthenticatorUser verification FIDO Authentication
… …SE
How is the key protected
(TPM, SE, TEE, …)?
Which user verification
method is used?

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ATTESTATION + METADATA
Private
attestation key
Signed Attestation Object
Metadata
Understand Authenticator
security characteristic by
looking into Metadata from
mds.fidoalliance.org
FIDO Registration
Verify using trust anchor
included in Metadata
Relying parties can store
this for auditing purposes

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FIDO AUTHENTICATORS
We see “Platform” Authenticators,
i.e. authenticators that are an
integral part of a smartphone or laptop.
We see “Roaming” Authenticators,
i.e. authenticators that can be connected to
different smartphones or laptops using
CTAP.
In both categories you find support for different modalities
Verify
User
Verify User
Presence

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HOW DOES FIDO WORK?
AuthenticatorUser verification FIDO Authentication
Same Authenticator
as registered before?
Same User as
enrolled before?
Can recognize the user (i.e.
user verification), but doesn’t
know its identity attributes.

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HOW DOES FIDO WORK?
AuthenticatorUser verification FIDO Authentication
Same Authenticator
as registered before?
Same User as
enrolled before?
Can recognize the user, but
doesn’t know its identity
attributes.
Identity binding to be
done outside FIDO:
This is “John Doe with
customer ID X”.

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FIDO REGISTRATION
Relying PartyAuthenticator
accountInfo, challenge, [cOpts]select Authenticator according to cOpts;
determine rpId, get tlsData;
clientData := {challenge, origin, rpId, hAlg, tlsData}
cOpts: crypto params, credential black list,
extensions
ai
verify user
generate:
key kpub
key kpriv
credential c
rpId, ai, hash(clientData), cryptoP, [exts]
cdh
c,kpub,clientData,ac,cdh,rpId,cntr,AAGUID[,exts],
signature(tbs)
s
tbs
c,kpub,clientData,ac,tbs, s
ac: attestation certificate chain
store:
key kpub
c

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FIDO AUTHENTICATION
Relying Party
rpId, [c,] hash(clientData)
select Authenticator according to policy;
check rpId, get tlsData (i.e. channel id, etc.);
lookup key handle h;
clientData := {challenge, rpId, tlsData}
clientData,cntr,[exts],signature(cdh,cntr,exts)
clientData, cntr, exts, s
lookup kpub
from DB
check:
exts +
signature
using
key kpub
s
cdh
challenge, [aOpts]
verify user
find
key kpriv
cntr++;
process exts
Authenticator

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FIDO BUILDING BLOCKS
(Roaming)
Authenticator
User Device
FIDO Client
(Platform)
Authenticator
ASM
RP App FIDO Authentication
RP App
Server
FIDO Server
Metadata

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FIDO BUILDING BLOCKS
(Roaming)
Authenticator
User Device
Browser
(Platform)
Authenticator
Platform
RP App FIDO Authentication
RP App
Server
FIDO Server
Metadata
Web
Authentication
JS API
CTAP

18. FIDO USER DEVICE
FIDO CLIENT
IdP
FIDO SERVER
FIDO
AUTHENTICATOR
FEDERATION SERVERBROWSER / APP FIDO Protocol
Service Provider
Federation
Id DB
Knows details about the
Authentication strength
Knows details about the
Identity and its
verification strength.
First Mile Second Mile
18
FIDO & FEDERATION
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WEB AUTHENTICATION
Supported In:
JavaScript API that enables
FIDO Authentication directly in web browsers

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FIDO AUTHENTICATION:
SECURITY & CONVENIENCE

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CONVENIENCE & SECURITY
Security
Convenience
Password

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CONVENIENCE & SECURITY
Security
Convenience
Password + OTP
Password

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CONVENIENCE & SECURITY
Security
Convenience
Password + OTP
Password
FIDO
In FIDO
• Same user verification method
for all servers
In FIDO: Arbitrary user verification
methods are supported
(+ they are interoperable)

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CONVENIENCE & SECURITY
Security
Convenience
Password + OTP
Password
FIDO
In FIDO: Scalable security
depending on Authenticator
implementation
In FIDO:
• Only public keys on server
• Not phishable

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CONCLUSION
• Different authentication use-cases lead to different
authentication requirements
• FIDO separates user verification from authentication and
hence supports all user verification methods
• FIDO supports scalable convenience & security
• User verification data never leaves the authenticator
• FIDO complements federation

26. 26
FIDO
TECHNICAL
OVERVIEW
Rolf Lindemann, Nok Nok Labs
rolf@noknok.com
Thank You
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