// SessionAnchor returns the decrypted and verified session anchor for KeyInit.
func (ki *KeyInit) SessionAnchor(sigPubKey string) (*SessionAnchor, error) {
// SIGKEYHASH corresponds to the SIGKEY of the Identity
pubKey, err := base64.Decode(sigPubKey)
if err != nil {
return nil, err
}
keyHash := cipher.SHA512(pubKey)
if ki.Contents.SIGKEYHASH != base64.Encode(cipher.SHA512(keyHash)) {
log.Error(ErrWrongSigKeyHash)
return nil, ErrWrongSigKeyHash
}
// verify that SESSIONANCHORHASH matches decrypted SESSIONANCHOR
enc, err := base64.Decode(ki.Contents.SESSIONANCHOR)
if err != nil {
return nil, err
}
txt := cipher.AES256CTRDecrypt(keyHash[:32], enc)
var sa SessionAnchor
if err := json.Unmarshal(txt, &sa); err != nil {
return nil, log.Error(err)
}
if ki.Contents.SESSIONANCHORHASH != base64.Encode(cipher.SHA512(sa.json())) {
log.Error(ErrSessionAnchor)
return nil, ErrSessionAnchor
}
return &sa, nil
}
// Decrypt decrypts the message reply and returns the resulting UIDIndex and
// UIDMesssage.
func (reply *MessageReply) Decrypt(UIDHash []byte) ([]byte, *Message, error) {
UIDMessageEncrypted, err := base64.Decode(reply.ENTRY.UIDMESSAGEENCRYPTED)
if err != nil {
return nil, nil, log.Error(err)
}
UIDIndex := UIDMessageEncrypted[:sha256.Size]
enc := UIDMessageEncrypted[sha256.Size:]
Message := cipher.AES256CTRDecrypt(UIDHash, enc)
uid, err := NewJSON(string(Message))
if err != nil {
return nil, nil, log.Error(err)
}
return UIDIndex, uid, nil
}