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>
228 lines
11 KiB
Go
Vendored
228 lines
11 KiB
Go
Vendored
package protocol
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import (
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"bytes"
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"crypto/x509"
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"encoding/asn1"
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"fmt"
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"github.com/duo-labs/webauthn/protocol/webauthncose"
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)
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var androidAttestationKey = "android-key"
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func init() {
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RegisterAttestationFormat(androidAttestationKey, verifyAndroidKeyFormat)
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}
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// From §8.4. https://www.w3.org/TR/webauthn/#android-key-attestation
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// The android-key attestation statement looks like:
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// $$attStmtType //= (
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// fmt: "android-key",
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// attStmt: androidStmtFormat
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// )
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// androidStmtFormat = {
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// alg: COSEAlgorithmIdentifier,
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// sig: bytes,
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// x5c: [ credCert: bytes, * (caCert: bytes) ]
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// }
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func verifyAndroidKeyFormat(att AttestationObject, clientDataHash []byte) (string, []interface{}, error) {
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// Given the verification procedure inputs attStmt, authenticatorData and clientDataHash, the verification procedure is as follows:
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// §8.4.1. Verify that attStmt is valid CBOR conforming to the syntax defined above and perform CBOR decoding on it to extract
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// the contained fields.
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// Get the alg value - A COSEAlgorithmIdentifier containing the identifier of the algorithm
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// used to generate the attestation signature.
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alg, present := att.AttStatement["alg"].(int64)
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if !present {
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return androidAttestationKey, nil, ErrAttestationFormat.WithDetails("Error retreiving alg value")
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}
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// Get the sig value - A byte string containing the attestation signature.
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sig, present := att.AttStatement["sig"].([]byte)
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if !present {
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return androidAttestationKey, nil, ErrAttestationFormat.WithDetails("Error retreiving sig value")
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}
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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 androidAttestationKey, nil, ErrAttestationFormat.WithDetails("Error retreiving x5c value")
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}
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// §8.4.2. Verify that sig is a valid signature over the concatenation of authenticatorData and clientDataHash
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// using the public key in the first certificate in x5c with the algorithm specified in alg.
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attCertBytes, valid := x5c[0].([]byte)
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if !valid {
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return androidAttestationKey, nil, ErrAttestation.WithDetails("Error getting certificate from x5c cert chain")
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}
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signatureData := append(att.RawAuthData, clientDataHash...)
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attCert, err := x509.ParseCertificate(attCertBytes)
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if err != nil {
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return androidAttestationKey, nil, ErrAttestationFormat.WithDetails(fmt.Sprintf("Error parsing certificate from ASN.1 data: %+v", err))
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}
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coseAlg := webauthncose.COSEAlgorithmIdentifier(alg)
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sigAlg := webauthncose.SigAlgFromCOSEAlg(coseAlg)
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err = attCert.CheckSignature(x509.SignatureAlgorithm(sigAlg), signatureData, sig)
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if err != nil {
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return androidAttestationKey, nil, ErrInvalidAttestation.WithDetails(fmt.Sprintf("Signature validation error: %+v\n", err))
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}
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// Verify that the public key in the first certificate in x5c matches the credentialPublicKey in the attestedCredentialData in authenticatorData.
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pubKey, err := webauthncose.ParsePublicKey(att.AuthData.AttData.CredentialPublicKey)
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if err != nil {
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return androidAttestationKey, nil, ErrInvalidAttestation.WithDetails(fmt.Sprintf("Error parsing public key: %+v\n", err))
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}
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e := pubKey.(webauthncose.EC2PublicKeyData)
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valid, err = e.Verify(signatureData, sig)
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if err != nil || valid != true {
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return androidAttestationKey, nil, ErrInvalidAttestation.WithDetails(fmt.Sprintf("Error parsing public key: %+v\n", err))
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}
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// §8.4.3. Verify that the attestationChallenge field in the attestation certificate extension data is identical to clientDataHash.
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// attCert.Extensions
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var attExtBytes []byte
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for _, ext := range attCert.Extensions {
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if ext.Id.Equal([]int{1, 3, 6, 1, 4, 1, 11129, 2, 1, 17}) {
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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 androidAttestationKey, nil, ErrAttestationFormat.WithDetails("Attestation certificate extensions missing 1.3.6.1.4.1.11129.2.1.17")
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}
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// As noted in §8.4.1 (https://w3c.github.io/webauthn/#key-attstn-cert-requirements) the Android Key Attestation attestation certificate's
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// android key attestation certificate extension data is identified by the OID "1.3.6.1.4.1.11129.2.1.17".
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decoded := keyDescription{}
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_, err = asn1.Unmarshal([]byte(attExtBytes), &decoded)
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if err != nil {
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return androidAttestationKey, nil, ErrAttestationFormat.WithDetails("Unable to parse Android key attestation certificate extensions")
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}
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// Verify that the attestationChallenge field in the attestation certificate extension data is identical to clientDataHash.
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if 0 != bytes.Compare(decoded.AttestationChallenge, clientDataHash) {
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return androidAttestationKey, nil, ErrAttestationFormat.WithDetails("Attestation challenge not equal to clientDataHash")
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}
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// The AuthorizationList.allApplications field is not present on either authorization list (softwareEnforced nor teeEnforced), since PublicKeyCredential MUST be scoped to the RP ID.
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if nil != decoded.SoftwareEnforced.AllApplications || nil != decoded.TeeEnforced.AllApplications {
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return androidAttestationKey, nil, ErrAttestationFormat.WithDetails("Attestation certificate extensions contains all applications field")
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}
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// For the following, use only the teeEnforced authorization list if the RP wants to accept only keys from a trusted execution environment, otherwise use the union of teeEnforced and softwareEnforced.
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// The value in the AuthorizationList.origin field is equal to KM_ORIGIN_GENERATED. (which == 0)
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if KM_ORIGIN_GENERATED != decoded.SoftwareEnforced.Origin || KM_ORIGIN_GENERATED != decoded.TeeEnforced.Origin {
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return androidAttestationKey, nil, ErrAttestationFormat.WithDetails("Attestation certificate extensions contains authorization list with origin not equal KM_ORIGIN_GENERATED")
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}
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// The value in the AuthorizationList.purpose field is equal to KM_PURPOSE_SIGN. (which == 2)
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if !contains(decoded.SoftwareEnforced.Purpose, KM_PURPOSE_SIGN) && !contains(decoded.TeeEnforced.Purpose, KM_PURPOSE_SIGN) {
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return androidAttestationKey, nil, ErrAttestationFormat.WithDetails("Attestation certificate extensions contains authorization list with purpose not equal KM_PURPOSE_SIGN")
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}
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return androidAttestationKey, x5c, err
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}
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func contains(s []int, e int) bool {
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for _, a := range s {
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if a == e {
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return true
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}
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}
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return false
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}
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type keyDescription struct {
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AttestationVersion int
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AttestationSecurityLevel asn1.Enumerated
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KeymasterVersion int
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KeymasterSecurityLevel asn1.Enumerated
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AttestationChallenge []byte
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UniqueID []byte
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SoftwareEnforced authorizationList
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TeeEnforced authorizationList
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}
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type authorizationList struct {
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Purpose []int `asn1:"tag:1,explicit,set,optional"`
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Algorithm int `asn1:"tag:2,explicit,optional"`
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KeySize int `asn1:"tag:3,explicit,optional"`
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Digest []int `asn1:"tag:5,explicit,set,optional"`
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Padding []int `asn1:"tag:6,explicit,set,optional"`
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EcCurve int `asn1:"tag:10,explicit,optional"`
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RsaPublicExponent int `asn1:"tag:200,explicit,optional"`
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RollbackResistance interface{} `asn1:"tag:303,explicit,optional"`
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ActiveDateTime int `asn1:"tag:400,explicit,optional"`
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OriginationExpireDateTime int `asn1:"tag:401,explicit,optional"`
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UsageExpireDateTime int `asn1:"tag:402,explicit,optional"`
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NoAuthRequired interface{} `asn1:"tag:503,explicit,optional"`
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UserAuthType int `asn1:"tag:504,explicit,optional"`
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AuthTimeout int `asn1:"tag:505,explicit,optional"`
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AllowWhileOnBody interface{} `asn1:"tag:506,explicit,optional"`
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TrustedUserPresenceRequired interface{} `asn1:"tag:507,explicit,optional"`
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TrustedConfirmationRequired interface{} `asn1:"tag:508,explicit,optional"`
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UnlockedDeviceRequired interface{} `asn1:"tag:509,explicit,optional"`
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AllApplications interface{} `asn1:"tag:600,explicit,optional"`
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ApplicationID interface{} `asn1:"tag:601,explicit,optional"`
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CreationDateTime int `asn1:"tag:701,explicit,optional"`
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Origin int `asn1:"tag:702,explicit,optional"`
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RootOfTrust rootOfTrust `asn1:"tag:704,explicit,optional"`
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OsVersion int `asn1:"tag:705,explicit,optional"`
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OsPatchLevel int `asn1:"tag:706,explicit,optional"`
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AttestationApplicationID []byte `asn1:"tag:709,explicit,optional"`
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AttestationIDBrand []byte `asn1:"tag:710,explicit,optional"`
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AttestationIDDevice []byte `asn1:"tag:711,explicit,optional"`
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AttestationIDProduct []byte `asn1:"tag:712,explicit,optional"`
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AttestationIDSerial []byte `asn1:"tag:713,explicit,optional"`
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AttestationIDImei []byte `asn1:"tag:714,explicit,optional"`
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AttestationIDMeid []byte `asn1:"tag:715,explicit,optional"`
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AttestationIDManufacturer []byte `asn1:"tag:716,explicit,optional"`
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AttestationIDModel []byte `asn1:"tag:717,explicit,optional"`
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VendorPatchLevel int `asn1:"tag:718,explicit,optional"`
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BootPatchLevel int `asn1:"tag:719,explicit,optional"`
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}
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type rootOfTrust struct {
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verifiedBootKey []byte
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deviceLocked bool
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verifiedBootState verifiedBootState
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verifiedBootHash []byte
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}
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type verifiedBootState int
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const (
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Verified verifiedBootState = iota
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SelfSigned
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Unverified
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Failed
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)
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/**
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* The origin of a key (or pair), i.e. where it was generated. Note that KM_TAG_ORIGIN can be found
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* in either the hardware-enforced or software-enforced list for a key, indicating whether the key
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* is hardware or software-based. Specifically, a key with KM_ORIGIN_GENERATED in the
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* hardware-enforced list is guaranteed never to have existed outide the secure hardware.
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*/
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type KM_KEY_ORIGIN int
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const (
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KM_ORIGIN_GENERATED = iota /* Generated in keymaster. Should not exist outside the TEE. */
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KM_ORIGIN_DERIVED /* Derived inside keymaster. Likely exists off-device. */
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KM_ORIGIN_IMPORTED /* Imported into keymaster. Existed as cleartext in Android. */
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KM_ORIGIN_UNKNOWN /* Keymaster did not record origin. This value can only be seen on
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* keys in a keymaster0 implementation. The keymaster0 adapter uses
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* this value to document the fact that it is unkown whether the key
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* was generated inside or imported into keymaster. */
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)
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/**
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* Possible purposes of a key (or pair).
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*/
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type KM_PURPOSE int
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const (
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KM_PURPOSE_ENCRYPT = iota /* Usable with RSA, EC and AES keys. */
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KM_PURPOSE_DECRYPT /* Usable with RSA, EC and AES keys. */
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KM_PURPOSE_SIGN /* Usable with RSA, EC and HMAC keys. */
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KM_PURPOSE_VERIFY /* Usable with RSA, EC and HMAC keys. */
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KM_PURPOSE_DERIVE_KEY /* Usable with EC keys. */
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KM_PURPOSE_WRAP /* Usable with wrapped keys. */
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)
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