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//nolint:unused // ignore unused types for now
package skae
import (
"crypto/x509"
"crypto/x509/pkix"
"encoding/asn1"
"errors"
"math/big"
"github.com/smallstep/go-attestation/attest"
)
var (
oidSubjectKeyAttestationEvidence = asn1.ObjectIdentifier{2, 23, 133, 6, 1, 1} // SKAE (Subject Key Attestation Evidence) OID: 2.23.133.6.1.1
oidAuthorityInfoAccessOcsp = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 48, 1}
oidAuthorityInfoAccessIssuers = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 48, 2}
)
func CreateSubjectKeyAttestationEvidenceExtension(_ *x509.Certificate, _ attest.CertificationParameters, _ bool) (pkix.Extension, error) {
return pkix.Extension{}, errors.New("not implemented yet") // return early; not verified to be working as expected yet
/*
asn1Issuer, err := asn1.Marshal(akCert.Issuer.ToRDNSequence()) //nolint:govet // intentionally breaking early
if err != nil {
return pkix.Extension{}, fmt.Errorf("error marshaling issuer: %w", err)
}
skaeExtension := asn1SKAE{
TCGSpecVersion: asn1TCGSpecVersion{Major: 2, Minor: 0},
KeyAttestationEvidence: asn1KeyAttestationEvidence{},
}
attestationEvidence := asn1AttestationEvidence{
TPMCertifyInfo: asn1TPMCertifyInfo{
CertifyInfo: asn1.BitString{ // TODO: check if setting the values like this is correct
Bytes: params.CreateAttestation,
BitLength: len(params.CreateAttestation) * 8,
},
Signature: asn1.BitString{
Bytes: params.CreateSignature,
BitLength: len(params.CreateSignature) * 8,
},
},
TPMIdentityCredAccessInfo: asn1TPMIdentityCredentialAccessInfo{
AuthorityInfoAccess: createAIA(akCert),
IssuerSerial: issuerAndSerial{
IssuerName: asn1.RawValue{FullBytes: asn1Issuer},
SerialNumber: akCert.SerialNumber,
},
},
}
aeb, err := asn1.Marshal(attestationEvidence)
if err != nil {
return pkix.Extension{}, fmt.Errorf("error marshaling attestation evidence: %w", err)
}
if !shouldEncrypt {
//skaeExtension.KeyAttestationEvidence.AttestEvidence = attestationEvidence
skaeExtension.KeyAttestationEvidence.Evidence = asn1.RawValue{
Class: asn1.ClassContextSpecific,
IsCompound: true,
Tag: 0, // CHOICE "0"
Bytes: aeb,
}
} else {
// TODO: encrypt the AttestEvidence to (right) recipient; set it as the EnvelopedAttestEvidence
encryptedAEB := aeb
eae := asn1EnvelopedAttestationEvidence{
RecipientInfos: []recipientInfo{}, // TODO: fill recipient(s)
EncryptedAttestInfo: asn1EncryptedAttestationInfo{
EncryptionAlgorithm: pkix.AlgorithmIdentifier{
Algorithm: nil, // TODO: select and fill
},
EncryptedAttestEvidence: encryptedAEB,
},
}
eaeBytes, err := asn1.Marshal(eae)
if err != nil {
return pkix.Extension{}, errors.New("error marshaling EnvelopedAttestationEvidence")
}
skaeExtension.KeyAttestationEvidence.Evidence = asn1.RawValue{
Class: asn1.ClassContextSpecific,
IsCompound: true,
Tag: 1, // CHOICE "1"
Bytes: eaeBytes,
}
return pkix.Extension{}, errors.New("encrypting the AttestEvidence is not yet supported")
}
skaeExtensionBytes, err := asn1.Marshal(skaeExtension)
if err != nil {
return pkix.Extension{}, fmt.Errorf("creating SKAE extension failed: %w", err)
}
result := pkix.Extension{
Id: oidSubjectKeyAttestationEvidence,
Critical: false, // non standard extension; don't break clients
Value: skaeExtensionBytes,
}
b, err := asn1.Marshal(result)
if err != nil {
return result, err
}
_ = b
return result, nil
*/
}
func createAIA(ak *x509.Certificate) []asn1AuthorityInfoAccessSyntax {
var aiaValues []asn1AuthorityInfoAccessSyntax
for _, server := range ak.OCSPServer {
aiaValues = append(aiaValues, asn1AuthorityInfoAccessSyntax{
Method: oidAuthorityInfoAccessOcsp,
Location: asn1.RawValue{Tag: asn1.TagOID, Class: asn1.ClassContextSpecific, Bytes: []byte(server)},
})
}
for _, url := range ak.IssuingCertificateURL {
aiaValues = append(aiaValues, asn1AuthorityInfoAccessSyntax{
Method: oidAuthorityInfoAccessIssuers,
Location: asn1.RawValue{Tag: asn1.TagOID, Class: asn1.ClassContextSpecific, Bytes: []byte(url)},
})
}
return aiaValues
}
type asn1SKAE struct {
TCGSpecVersion asn1TCGSpecVersion
KeyAttestationEvidence asn1KeyAttestationEvidence
}
type asn1TCGSpecVersion struct {
Major int
Minor int
}
type asn1KeyAttestationEvidence struct {
// AttestEvidence asn1AttestationEvidence // TODO: ASN1 CHOICE between those two
// EnvelopedAttestEvidence asn1EnvelopedAttestationEvidence
Evidence asn1.RawValue
}
type asn1AttestationEvidence struct {
TPMCertifyInfo asn1TPMCertifyInfo
TPMIdentityCredAccessInfo asn1TPMIdentityCredentialAccessInfo
}
type asn1TPMCertifyInfo struct {
CertifyInfo asn1.BitString
Signature asn1.BitString
}
type asn1TPMIdentityCredentialAccessInfo struct {
AuthorityInfoAccess []asn1AuthorityInfoAccessSyntax
IssuerSerial issuerAndSerial
}
type asn1AuthorityInfoAccessSyntax struct {
Method asn1.ObjectIdentifier
Location asn1.RawValue
}
type issuerAndSerial struct {
IssuerName asn1.RawValue
SerialNumber *big.Int
}
type asn1EnvelopedAttestationEvidence struct {
RecipientInfos []recipientInfo `asn1:"set"`
EncryptedAttestInfo asn1EncryptedAttestationInfo
}
type recipientInfo struct {
Version int
IssuerAndSerialNumber issuerAndSerial
KeyEncryptionAlgorithm pkix.AlgorithmIdentifier
EncryptedKey []byte
}
type asn1EncryptedAttestationInfo struct {
EncryptionAlgorithm pkix.AlgorithmIdentifier
EncryptedAttestEvidence []byte // -- The ciphertext resulting from the encryption of DER-encoded AttestationEvidence (against public key in recipientinfo; something like that)
}
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