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package plugin
import (
"crypto/subtle"
"errors"
"fmt"
"filippo.io/age"
"filippo.io/age/tag"
"filippo.io/hpke"
"github.com/google/go-tpm/tpm2/transport"
)
// TPMTagIdentity implements the p256tag identity handler
type TPMTagIdentity struct {
tpm transport.TPMCloser
identity *Identity
pin func() ([]byte, error)
}
func NewTPMTagIdentity(tpm transport.TPMCloser, pin func() ([]byte, error), identity *Identity) *TPMTagIdentity {
return &TPMTagIdentity{tpm, identity, pin}
}
var _ age.Identity = &TPMTagIdentity{}
func (t *TPMTagIdentity) unwrap(block *age.Stanza) ([]byte, error) {
if len(block.Args) < 2 || block.Type != "p256tag" {
return nil, age.ErrIncorrectIdentity
}
tag, err := b64Decode(block.Args[0])
if err != nil {
return nil, fmt.Errorf("failed base64 decode session key: %v", err)
}
sessionKey, err := b64Decode(block.Args[1])
if err != nil {
return nil, fmt.Errorf("failed base64 decode session key: %v", err)
}
rsp, err := t.identity.Recipient()
if err != nil {
return nil, fmt.Errorf("unwrap: failed to get recipient from identity %v", err)
}
itag, err := rsp.Tag(sessionKey)
if err != nil {
return nil, fmt.Errorf("unwrap: failed to get tag from recipient: %v", err)
}
// Check if we are dealing with the correct key
if subtle.ConstantTimeCompare(tag, itag) != 1 {
return nil, age.ErrIncorrectIdentity
}
var pin []byte
if t.identity.HasPIN() {
pin, err = t.pin()
if err != nil {
return nil, fmt.Errorf("failed to get pin: %v", err)
}
}
k, err := hpke.NewDHKEMPrivateKey(NewTPMKeyExchange(t.tpm, pin, t.identity))
if err != nil {
return nil, fmt.Errorf("failed to unwrap file key: %v", err)
}
r, err := hpke.NewRecipient(sessionKey, k, hpke.HKDFSHA256(), hpke.ChaCha20Poly1305(), []byte("age-encryption.org/p256tag"))
if err != nil {
return nil, fmt.Errorf("failed to unwrap file key: %v", err)
}
return r.Open(nil, block.Body)
}
func (t *TPMTagIdentity) Unwrap(stanzas []*age.Stanza) ([]byte, error) {
for _, s := range stanzas {
fileKey, err := t.unwrap(s)
if errors.Is(err, age.ErrIncorrectIdentity) {
continue
}
if err != nil {
return nil, err
}
return fileKey, nil
}
return nil, age.ErrIncorrectIdentity
}
func (t *TPMTagIdentity) Recipient() *tag.Recipient {
resp, err := NewTagRecipient(t.identity.publickey)
if err != nil {
panic("this is unexpected")
}
return resp
}
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