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@ -6,6 +6,8 @@ import (
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"crypto/sha256"
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"crypto/subtle"
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"crypto/tls"
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"crypto/x509"
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"crypto/x509/pkix"
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"encoding/asn1"
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"encoding/base64"
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"encoding/hex"
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@ -19,6 +21,10 @@ import (
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"strings"
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"time"
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"github.com/fxamacker/cbor/v2"
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"github.com/google/go-attestation/attest"
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"github.com/google/go-attestation/oid"
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x509ext "github.com/google/go-attestation/x509"
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"go.step.sm/crypto/jose"
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)
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@ -301,9 +307,84 @@ func dns01Validate(ctx context.Context, ch *Challenge, db DB, jwk *jose.JSONWebK
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return nil
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}
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type Payload struct {
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AttStmt []byte `json:"attStmt"`
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}
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type AttestationObject struct {
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Format string `json:"fmt"`
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AttStatement map[string]interface{} `json:"attStmt,omitempty"`
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}
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// TODO(bweeks): move attestation verification to a shared package.
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// TODO(bweeks): define new error type for failed attestation validation.
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func deviceAttest01Validate(ctx context.Context, ch *Challenge, db DB, jwk *jose.JSONWebKey, payload []byte) error {
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if string(payload) != "\"fake_device_attestation_statement\"" {
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return errors.New("string(payload) != \"fake_device_attestation_statement\"")
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var p Payload
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if err := json.Unmarshal(payload, &p); err != nil {
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return WrapErrorISE(err, "error unmarshalling JSON")
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}
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att := AttestationObject{}
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if err := cbor.Unmarshal(p.AttStmt, &att); err != nil {
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return WrapErrorISE(err, "error unmarshalling CBOR")
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}
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// TODO(bweeks): move verification code to a shared package.
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// begin TPM key certification verification
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params := &attest.CertificationParameters{
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Public: att.AttStatement["pubArea"].([]byte),
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CreateAttestation: att.AttStatement["certInfo"].([]byte),
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CreateSignature: att.AttStatement["sig"].([]byte),
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}
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// end TPM key certification verification
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x5c, x509present := att.AttStatement["x5c"].([]interface{})
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if !x509present {
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return errors.New("x5c not present")
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}
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akCertBytes, valid := x5c[0].([]byte)
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if !valid {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"error getting certificate from x5c cert chain"))
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}
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akCert, err := x509.ParseCertificate(akCertBytes)
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if err != nil {
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return WrapErrorISE(err, "error parsing AK certificate")
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}
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if err := params.Verify(attest.VerifyOpts{Public: akCert.PublicKey, Hash: crypto.SHA256}); err != nil {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"params.Verify failed: %v", err))
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}
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var sanExt pkix.Extension
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for _, ext := range akCert.Extensions {
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if ext.Id.Equal(oid.SubjectAltName) {
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sanExt = ext
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}
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}
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if sanExt.Value == nil {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"akCert missing subjectAltName"))
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}
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san, err := x509ext.ParseSubjectAltName(sanExt)
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if err != nil {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"failed to parse subjectAltName"))
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}
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if len(san.PermanentIdentifiers) != 1 {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"subjectAltName doesn't contain a PermanentIdentifier"))
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}
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wantPermID := san.PermanentIdentifiers[0]
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if wantPermID.IdentifierValue != ch.Value {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"identifier from certificate and challenge do not match"))
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}
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// Update and store the challenge.
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Brandon Weeks
2 years ago