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package protocol
import (
"crypto/subtle"
"fmt"
"net/url"
"strings"
)
// CollectedClientData represents the contextual bindings of both the WebAuthn Relying Party
// and the client. It is a key-value mapping whose keys are strings. Values can be any type
// that has a valid encoding in JSON. Its structure is defined by the following Web IDL.
// https://www.w3.org/TR/webauthn/#sec-client-data
type CollectedClientData struct {
// Type the string "webauthn.create" when creating new credentials,
// and "webauthn.get" when getting an assertion from an existing credential. The
// purpose of this member is to prevent certain types of signature confusion attacks
//(where an attacker substitutes one legitimate signature for another).
Type CeremonyType `json:"type"`
Challenge string `json:"challenge"`
Origin string `json:"origin"`
TokenBinding *TokenBinding `json:"tokenBinding,omitempty"`
// Chromium (Chrome) returns a hint sometimes about how to handle clientDataJSON in a safe manner
Hint string `json:"new_keys_may_be_added_here,omitempty"`
}
type CeremonyType string
const (
CreateCeremony CeremonyType = "webauthn.create"
AssertCeremony CeremonyType = "webauthn.get"
)
type TokenBinding struct {
Status TokenBindingStatus `json:"status"`
ID string `json:"id,omitempty"`
}
type TokenBindingStatus string
const (
// Indicates token binding was used when communicating with the
// Relying Party. In this case, the id member MUST be present.
Present TokenBindingStatus = "present"
// Indicates token binding was used when communicating with the
// negotiated when communicating with the Relying Party.
Supported TokenBindingStatus = "supported"
// Indicates token binding not supported
// when communicating with the Relying Party.
NotSupported TokenBindingStatus = "not-supported"
)
// Returns the origin per the HTML spec: (scheme)://(host)[:(port)]
func FullyQualifiedOrigin(u *url.URL) string {
return fmt.Sprintf("%s://%s", u.Scheme, u.Host)
}
// Handles steps 3 through 6 of verfying the registering client data of a
// new credential and steps 7 through 10 of verifying an authentication assertion
// See https://www.w3.org/TR/webauthn/#registering-a-new-credential
// and https://www.w3.org/TR/webauthn/#verifying-assertion
func (c *CollectedClientData) Verify(storedChallenge string, ceremony CeremonyType, relyingPartyOrigin string) error {
// Registration Step 3. Verify that the value of C.type is webauthn.create.
// Assertion Step 7. Verify that the value of C.type is the string webauthn.get.
if c.Type != ceremony {
err := ErrVerification.WithDetails("Error validating ceremony type")
err.WithInfo(fmt.Sprintf("Expected Value: %s\n Received: %s\n", ceremony, c.Type))
return err
}
// Registration Step 4. Verify that the value of C.challenge matches the challenge
// that was sent to the authenticator in the create() call.
// Assertion Step 8. Verify that the value of C.challenge matches the challenge
// that was sent to the authenticator in the PublicKeyCredentialRequestOptions
// passed to the get() call.
challenge := c.Challenge
if subtle.ConstantTimeCompare([]byte(storedChallenge), []byte(challenge)) != 1 {
err := ErrVerification.WithDetails("Error validating challenge")
return err.WithInfo(fmt.Sprintf("Expected b Value: %#v\nReceived b: %#v\n", storedChallenge, challenge))
}
// Registration Step 5 & Assertion Step 9. Verify that the value of C.origin matches
// the Relying Party's origin.
clientDataOrigin, err := url.Parse(c.Origin)
if err != nil {
return ErrParsingData.WithDetails("Error decoding clientData origin as URL")
}
if !strings.EqualFold(FullyQualifiedOrigin(clientDataOrigin), relyingPartyOrigin) {
err := ErrVerification.WithDetails("Error validating origin")
return err.WithInfo(fmt.Sprintf("Expected Value: %s\n Received: %s\n", relyingPartyOrigin, FullyQualifiedOrigin(clientDataOrigin)))
}
// Registration Step 6 and Assertion Step 10. Verify that the value of C.tokenBinding.status
// matches the state of Token Binding for the TLS connection over which the assertion was
// obtained. If Token Binding was used on that TLS connection, also verify that C.tokenBinding.id
// matches the base64url encoding of the Token Binding ID for the connection.
if c.TokenBinding != nil {
if c.TokenBinding.Status == "" {
return ErrParsingData.WithDetails("Error decoding clientData, token binding present without status")
}
if c.TokenBinding.Status != Present && c.TokenBinding.Status != Supported && c.TokenBinding.Status != NotSupported {
return ErrParsingData.WithDetails("Error decoding clientData, token binding present with invalid status").WithInfo(fmt.Sprintf("Got: %s\n", c.TokenBinding.Status))
}
}
// Not yet fully implemented by the spec, browsers, and me.
return nil
}
|
