The document discusses the W3C Web Authentication standard (also known as FIDO 2.0) for passwordless strong authentication on the web. It provides an overview of the key components and actors in the standard like FIDO authenticators, user agents, relying parties. It then summarizes the basic flows of registration and authentication in 2 phases. During registration, a key pair is generated on the authenticator and the public key is registered with the FIDO server. During authentication, the authenticator performs local authentication using the registered key and sends an assertion to the server for remote authentication.

1. W3C Web Authentication
(a.k.a. FIDO 2.0)
@nov

2. #idcon vol.20 - またの名を #fidcon
https://idcon.org

3. Overview
FIDO Authenticator
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server

4. FIDO の基本的な流れ
❖ Registration と Authentication の2フェーズ
❖ Registration
❖ FIDO Authenticator 内で鍵ペアを生成し公開鍵を FIDO Server に登録
❖ Authentication
❖ 登録済の鍵を持つ FIDO Authenticator でローカル認証
❖ FIDO Assertion を FIDO Server に送ってリモート認証

5. Registration
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server

6. Registration
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
Init
Reg. Request

7. Registration
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
init
Register Request

8. Registration
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
init
Reg. Request
Select Authenticator
&
Authenticate

9. Registration
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
init
Reg. Request
Select Authenticator
&
Authenticate
Key Generation

10. Registration
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
init
Reg. Request
AttestationAuth
Key Generation

11. Registration
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
init
Reg. Request
Reg. Response
AttestationAuth
Key Generation

12. Registration
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
init
Reg. Request
Select Authenticator
&
Authenticate
Reg. Response

13. Registration
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
init
Reg. Request
Reg. Response
Verify Authenticator
Key Generation
AttestationAuth

14. Authentication
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server

15. Authentication
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
Init
Auth Request

16. Authentication
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
Init
Auth Request

17. Authentication
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
Init
Auth Request
AssertionAuth
Fetch Key

18. Authentication
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
Auth Response
Init
Auth Request
AssertionAuth

19. Authentication
User Agent
End-User Device
FIDO Authenticator
FIDO Client
Relying Party
Web Apps
FIDO Authenticator
Metadata
FIDO Server
Authenticate
Auth Response
Init
Auth Request

20. ❖ Web AuthN 仕様的には (一部) 考慮されて
いるように見えるが、現状実装はなし。
❖ まだ解決すべき課題が残っている、らしい。
❖ 詳細は後の関水さんの発表で。
❖ Chrome, FireFox, Edge が実装済。
❖ WebKit も実装は開始している痕跡有。
❖ この発表ではこちらを扱う。

21. W3C Web Authentication

22. https://www.w3.org/TR/webauthn

23. W3C Web Authentication
❖ 対象は Browser, FIDO Authenticator, FIDO Server
❖ FIDO Server 側の処理については後ほど倉林くんから
❖ この発表では JS API の話をメインに
❖ Browser and/or FIDO Authenticator 作る人は自分で頑張れ (!?)
❖ JS API Interface は W3C Credential Management API (*1) ベース
❖ “public-key” という Credential Type を追加定義
(*1) Credential Management API については #idcon vol.23 参照

24. https://web-authn.self-issued.app/u2f.js

25. https://web-authn.self-issued.app/u2f.js

26. https://web-authn.self-issued.app/u2f.js
※ 現状利用する鍵を指定する必要あり。

27. allowCredentials 必須 = U2F 相当
(chrome v68.0.3432.3)

28. open "Google Chrome (dev).app” --args
--enable-features=WebAuthenticationCtap2

29. CTAP2 Authenticators?

30. FIDO Attestation & Assertion

31. FIDO Attestation
(Registration Response)

32. URL-safe Base64 Encoded JSON
URL-safe Base64 Encoded CBOR Obj
※ CBOR については @ritou より

33. Decoded Attestation Object

34. authData contains..
Name Length (in bytes) Description
rpIdHash 32 SHA-256 hash of the RP ID associated with the credential.
flags 1
Flags (bit 0 is the least significant bit):
• Bit 0: User Present (UP) result.
• Bit 1: Reserved for future use (RFU1).
• Bit 2: User Verified (UV) result.
• Bits 3-5: Reserved for future use (RFU2).
• Bit 6: Attested credential data included (AT).
• Bit 7: Extension data included (ED).
signCount 4 Signature counter, 32-bit unsigned big-endian integer.
attestedCredentialData variable (if present)
attested credential data (if present). See §6.3.1 Attested credential
data for details. Its length depends on the length of the credential ID
and credential public key being attested.
extensions variable (if present)
Extension-defined authenticator data. This is a CBOR [RFC7049]
map with extension identifiers as keys, and authenticator extension
outputs as values. See §9 WebAuthn Extensions for details.

35. attestedCredentialData contains..
Name Length (in bytes) Description
aaguid 16 The AAGUID of the authenticator.
credentialIdLength 2 Byte length L of Credential ID, 16-bit unsigned big-endian integer.
credentialId L Credential ID
credentialPublicKey variable
The credential public key encoded in COSE_Key format, as defined
in Section 7 of [RFC8152], using the CTAP2 canonical CBOR
encoding form. The COSE_Key-encoded credential public key MUST
contain the optional "alg" parameter and MUST NOT contain any
other optional parameters. The "alg" parameter MUST contain a
COSEAlgorithmIdentifier value. The encoded credential public
key MUST also contain any additional required parameters stipulated
by the relevant key type specification, i.e., required for the key type
"kty" and algorithm "alg" (see Section 8 of [RFC8152]).

36. Credential Public Key
※ 実際には COSE Key フォーマット

37. Decoded Client Data JSON

38. FIDO Assertion
(Authentication Response)

39. Decoded Client Data JSON

40. authData contains..
Name Length (in bytes) Description
rpIdHash 32 SHA-256 hash of the RP ID associated with the credential.
flags 1
Flags (bit 0 is the least significant bit):
• Bit 0: User Present (UP) result.
• Bit 1: Reserved for future use (RFU1).
• Bit 2: User Verified (UV) result.
• Bits 3-5: Reserved for future use (RFU2).
• Bit 6: Attested credential data included (AT).
• Bit 7: Extension data included (ED).
signCount 4 Signature counter, 32-bit unsigned big-endian integer.
attestedCredentialData variable (if present)
attested credential data (if present). See §6.3.1 Attested credential
data for details. Its length depends on the length of the credential ID
and credential public key being attested.
extensions variable (if present)
Extension-defined authenticator data. This is a CBOR [RFC7049]
map with extension identifiers as keys, and authenticator extension
outputs as values. See §9 WebAuthn Extensions for details.

41. Android OS as FIDO Authenticator

42. What's new in Android security (Google I/O '18)

43. iOS as FIDO Authenticator?

44. https://github.com/WebKit/webkit/blob/master/Source/
WebCore/Modules/webauthn/cocoa/LocalAuthenticator.mm