When we send request for credential.create
we get back attestationObject
which contains PublicKey within CBOR format, but when we call credential.get
we have only authenticatorData
without PublicKey data. So is it possible to retrieve PublicKey from Passkey, after credential.create
call?
The issue is when we created a Passkey we can have connectivity problem so the PublicKey store request to backend will fail, but passkey itself is already created and we can't check the signature without PublicKey next time user want to SignIn!
credential.create
request
{
"challenge": "nhkQXfE59Jb97VyyNJkvDiXucMEvltduvcrDmGrODHY",
"rp": {
"name": "CredMan App Test",
"id": "credential-manager-app-test.glitch.me"
},
"user": {
"id": "2HzoHm_hY0CjuEESY9tY6-3SdjmNHOoNqaPDcZGzsr0",
"name": "[email protected]",
"displayName": "[email protected]"
},
"pubKeyCredParams": [
{
"type": "public-key",
"alg": -7
},
{
"type": "public-key",
"alg": -257
}
],
"timeout": 1800000,
"attestation": "none",
"excludeCredentials": [],
"authenticatorSelection": {
"authenticatorAttachment": "platform",
"requireResidentKey": true,
"residentKey": "required",
"userVerification": "required"
}
}
credential.create
response
{
"id": "KEDetxZcUfinhVi6Za5nZQ",
"type": "public-key",
"rawId": "KEDetxZcUfinhVi6Za5nZQ",
"response": {
"clientDataJSON": "eyJ0eXBlIjoid2ViYXV0aG4uY3JlYXRlIiwiY2hhbGxlbmdlIjoibmhrUVhmRTU5SmI5N1Z5eU5Ka3ZEaVh1Y01Fdmx0ZHV2Y3JEbUdyT0RIWSIsIm9yaWdpbiI6ImFuZHJvaWQ6YXBrLWtleS1oYXNoOk1MTHpEdll4UTRFS1R3QzZVNlpWVnJGUXRIOEdjVi0xZDQ0NEZLOUh2YUkiLCJhbmRyb2lkUGFja2FnZU5hbWUiOiJjb20uZ29vZ2xlLmNyZWRlbnRpYWxtYW5hZ2VyLnNhbXBsZSJ9",
"attestationObject": "o2NmbXRkbm9uZWdhdHRTdG10oGhhdXRoRGF0YViUj5r_fLFhV-qdmGEwiukwD5E_5ama9g0hzXgN8thcFGRdAAAAAAAAAAAAAAAAAAAAAAAAAAAAEChA3rcWXFH4p4VYumWuZ2WlAQIDJiABIVgg4RqZaJyaC24Pf4tT-8ONIZ5_Elddf3dNotGOx81jj3siWCAWXS6Lz70hvC2g8hwoLllOwlsbYatNkO2uYFO-eJID6A"
}
}
credential.get
request
{
"challenge": "T1xCsnxM2DNL2KdK5CLa6fMhD7OBqho6syzInk_n-Uo",
"allowCredentials": [],
"timeout": 1800000,
"userVerification": "required",
"rpId": "credential-manager-app-test.glitch.me"
}
credential.get
response
{
"id": "KEDetxZcUfinhVi6Za5nZQ",
"type": "public-key",
"rawId": "KEDetxZcUfinhVi6Za5nZQ",
"response": {
"clientDataJSON": "eyJ0eXBlIjoid2ViYXV0aG4uZ2V0IiwiY2hhbGxlbmdlIjoiVDF4Q3NueE0yRE5MMktkSzVDTGE2Zk1oRDdPQnFobzZzeXpJbmtfbi1VbyIsIm9yaWdpbiI6ImFuZHJvaWQ6YXBrLWtleS1oYXNoOk1MTHpEdll4UTRFS1R3QzZVNlpWVnJGUXRIOEdjVi0xZDQ0NEZLOUh2YUkiLCJhbmRyb2lkUGFja2FnZU5hbWUiOiJjb20uZ29vZ2xlLmNyZWRlbnRpYWxtYW5hZ2VyLnNhbXBsZSJ9",
"authenticatorData": "j5r_fLFhV-qdmGEwiukwD5E_5ama9g0hzXgN8thcFGQdAAAAAA",
"signature": "MEUCIQCO1Cm4SA2xiG5FdKDHCJorueiS04wCsqHhiRDbbgITYAIgMKMFirgC2SSFmxrh7z9PzUqr0bK1HZ6Zn8vZVhETnyQ",
"userHandle": "2HzoHm_hY0CjuEESY9tY6-3SdjmNHOoNqaPDcZGzsr0"
}
}
Can't see anything in Webauthn doc according to that problem
Fundamentally, the other answers are correct: if you missed the registration, you can't trust a random public key that is presented at assertion time!
Narrowly, however, if you're using ECDSA (which is extremely likely) then, given a signed message and a signature (both of which you have at assertion time), you can solve for the public key modulo the sign of the curve point. With two signatures from the same key, you can resolve the sign bit too.