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package tpm2
import (
"io"
)
var (
labelIdentity = "IDENTITY"
)
// CreateCredential creates an encrypted secret that can be recovered using ActivateCredential as part of a key-attestation flow.
func CreateCredential(rand io.Reader, pub LabeledEncapsulationKey, name []byte, credentialValue []byte) (idObject []byte, encSecret []byte, err error) {
secret, ciphertext, err := pub.Encapsulate(rand, labelIdentity)
if err != nil {
return nil, nil, err
}
// Marshal the credentialValue as a TPM2B_DIGEST before encrypting it.
// See Part 1, "Credential Protection", and Part 2, "TPMS_ID_OBJECT".
credential2B := Marshal(TPM2BDigest{Buffer: credentialValue})
// Encrypt the credentialValue as encIdentity.
encIdentity, err := deriveAndEncrypt(pub, secret, name, credential2B)
if err != nil {
return nil, nil, err
}
// Compute the HMAC of (encIdentity || name)
identityHMAC, err := deriveAndHMAC(pub, secret, nil, encIdentity, name)
if err != nil {
return nil, nil, err
}
// Marshal the virtual TPMS_ID_OBJECT ourselves. We have to do this since encIdentity's size is encrypted.
idObject = make([]byte, 0, 2+len(identityHMAC)+len(encIdentity))
idObject = append(idObject, Marshal(TPM2BDigest{Buffer: identityHMAC})...)
idObject = append(idObject, encIdentity...)
return idObject, ciphertext, nil
}
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