func newHeader(
sender, recipient *uid.Message,
recipientTempHash string,
senderSessionPub, nextSenderSessionPub,
nextRecipientSessionPubSeen *uid.KeyEntry,
nymAddress string,
senderSessionCount, senderMessageCount uint64,
senderLastKeychainHash string,
rand io.Reader,
statusCode StatusCode,
) (*header, error) {
if len(senderLastKeychainHash) != hashchain.EntryBase64Len {
return nil, log.Errorf("msg: last hashchain entry '%s' does not have base64 length %d (but %d)",
senderLastKeychainHash, hashchain.EntryBase64Len, len(senderLastKeychainHash))
}
h := &header{
Ciphersuite: uid.DefaultCiphersuite, // at the moment we only support one ciphersuite
RecipientPubHash: recipient.PubHash(),
RecipientTempHash: recipientTempHash,
SenderIdentity: sender.Identity(),
SenderSessionPub: *senderSessionPub,
SenderIdentityPubHash: sender.PubHash(),
SenderIdentityPub: *sender.PubKey(),
NextSenderSessionPub: nextSenderSessionPub,
NextRecipientSessionPubSeen: nextRecipientSessionPubSeen,
NymAddress: nymAddress,
MaxDelay: 0, // TODO
SenderSessionCount: senderSessionCount,
SenderMessageCount: senderMessageCount,
SenderUID: string(sender.JSON()),
SenderLastKeychainHash: senderLastKeychainHash,
Status: statusCode,
Padding: "", // is set below
}
// calculate padding length
padLen := wiggleRoom
// pad sender identity
if len(h.SenderIdentity) > identity.MaxLen {
return nil, log.Error("msg: sender identity is too long")
}
padLen += identity.MaxLen - len(h.SenderIdentity)
// pad nextSenderSessionPub
if nextSenderSessionPub == nil {
padLen += length.KeyEntryECDHE25519 - length.Nil
}
// pad nextRecipientSessionPubSeen
if nextRecipientSessionPubSeen == nil {
padLen += length.KeyEntryECDHE25519 - length.Nil
}
// pad nym address
if len(h.NymAddress) > length.MaxNymAddress {
return nil, log.Error("msg: nym address is too long")
}
padLen += length.MaxNymAddress - len(h.NymAddress)
// pad integers
padLen += 20 - digits.Count(h.MaxDelay)
padLen += 20 - digits.Count(h.SenderSessionCount)
padLen += 20 - digits.Count(h.SenderMessageCount)
// pad sender UIDMessage
if len(h.SenderUID) > length.MaxUIDMessage {
return nil, log.Error("msg: sender UIDMesssage is too long")
}
padLen += length.MaxUIDMessage - len(h.SenderUID)
// generate padding
randLen := padLen/2 + padLen%2
pad, err := padding.Generate(randLen, cipher.RandReader)
if err != nil {
return nil, err
}
// set padding
p := hex.EncodeToString(pad)
if padLen%2 == 1 {
p = p[:len(p)-1]
}
h.Padding = p
return h, nil
}
