35c3553870
Migrate from U2F to Webauthn Co-authored-by: Andrew Thornton <art27@cantab.net> Co-authored-by: 6543 <6543@obermui.de> Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
104 lines
3.7 KiB
Go
Vendored
104 lines
3.7 KiB
Go
Vendored
package protocol
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import (
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"bytes"
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"crypto/ecdsa"
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"crypto/elliptic"
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"crypto/sha256"
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"crypto/x509"
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"encoding/asn1"
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"fmt"
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"math/big"
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"github.com/duo-labs/webauthn/protocol/webauthncose"
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)
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var appleAttestationKey = "apple"
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func init() {
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RegisterAttestationFormat(appleAttestationKey, verifyAppleKeyFormat)
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}
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// From §8.8. https://www.w3.org/TR/webauthn-2/#sctn-apple-anonymous-attestation
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// The apple attestation statement looks like:
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// $$attStmtType //= (
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// fmt: "apple",
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// attStmt: appleStmtFormat
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// )
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// appleStmtFormat = {
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// x5c: [ credCert: bytes, * (caCert: bytes) ]
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// }
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func verifyAppleKeyFormat(att AttestationObject, clientDataHash []byte) (string, []interface{}, error) {
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// Step 1. Verify that attStmt is valid CBOR conforming to the syntax defined
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// above and perform CBOR decoding on it to extract the contained fields.
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// If x5c is not present, return an error
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x5c, x509present := att.AttStatement["x5c"].([]interface{})
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if !x509present {
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// Handle Basic Attestation steps for the x509 Certificate
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return appleAttestationKey, nil, ErrAttestationFormat.WithDetails("Error retreiving x5c value")
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}
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credCertBytes, valid := x5c[0].([]byte)
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if !valid {
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return appleAttestationKey, nil, ErrAttestation.WithDetails("Error getting certificate from x5c cert chain")
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}
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credCert, err := x509.ParseCertificate(credCertBytes)
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if err != nil {
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return appleAttestationKey, nil, ErrAttestationFormat.WithDetails(fmt.Sprintf("Error parsing certificate from ASN.1 data: %+v", err))
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}
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// Step 2. Concatenate authenticatorData and clientDataHash to form nonceToHash.
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nonceToHash := append(att.RawAuthData, clientDataHash...)
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// Step 3. Perform SHA-256 hash of nonceToHash to produce nonce.
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nonce := sha256.Sum256(nonceToHash)
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// Step 4. Verify that nonce equals the value of the extension with OID 1.2.840.113635.100.8.2 in credCert.
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var attExtBytes []byte
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for _, ext := range credCert.Extensions {
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if ext.Id.Equal([]int{1, 2, 840, 113635, 100, 8, 2}) {
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attExtBytes = ext.Value
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}
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}
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if len(attExtBytes) == 0 {
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return appleAttestationKey, nil, ErrAttestationFormat.WithDetails("Attestation certificate extensions missing 1.2.840.113635.100.8.2")
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}
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decoded := AppleAnonymousAttestation{}
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_, err = asn1.Unmarshal([]byte(attExtBytes), &decoded)
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if err != nil {
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return appleAttestationKey, nil, ErrAttestationFormat.WithDetails("Unable to parse apple attestation certificate extensions")
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}
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if !bytes.Equal(decoded.Nonce, nonce[:]) || err != nil {
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return appleAttestationKey, nil, ErrInvalidAttestation.WithDetails("Attestation certificate does not contain expected nonce")
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}
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// Step 5. Verify that the credential public key equals the Subject Public Key of credCert.
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// TODO: Probably move this part to webauthncose.go
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pubKey, err := webauthncose.ParsePublicKey(att.AuthData.AttData.CredentialPublicKey)
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if err != nil {
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return appleAttestationKey, nil, ErrInvalidAttestation.WithDetails(fmt.Sprintf("Error parsing public key: %+v\n", err))
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}
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credPK := pubKey.(webauthncose.EC2PublicKeyData)
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subjectPK := credCert.PublicKey.(*ecdsa.PublicKey)
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credPKInfo := &ecdsa.PublicKey{
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Curve: elliptic.P256(),
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X: big.NewInt(0).SetBytes(credPK.XCoord),
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Y: big.NewInt(0).SetBytes(credPK.YCoord),
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}
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if !credPKInfo.Equal(subjectPK) {
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return appleAttestationKey, nil, ErrInvalidAttestation.WithDetails("Certificate public key does not match public key in authData")
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}
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// Step 6. If successful, return implementation-specific values representing attestation type Anonymization CA and attestation trust path x5c.
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return appleAttestationKey, x5c, nil
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}
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// Apple has not yet publish schema for the extension(as of JULY 2021.)
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type AppleAnonymousAttestation struct {
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Nonce []byte `asn1:"tag:1,explicit"`
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}
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