func deriveKeys(chainKey []byte, kdf io.Reader) (send, recv []string, err error) {
buffer := make([]byte, 64)
for i := 0; i < msg.NumOfFutureKeys; i++ {
if _, err := io.ReadFull(kdf, buffer); err != nil {
return nil, nil, err
}
send = append(send, base64.Encode(cipher.HMAC(chainKey, buffer)))
if _, err := io.ReadFull(kdf, buffer); err != nil {
return nil, nil, err
}
recv = append(recv, base64.Encode(cipher.HMAC(chainKey, buffer)))
}
return
}
// generateMessageKeys generates the next numOfKeys many session keys from
// from rootKey for given senderIdentity and recipientIdentity.
// If recipientKeys is true the generated sender and reciever keys are stored in
// reverse order.
// It uses senderSessionPub and recipientPub in the process and calls
// keyStore.StoresSession and keyStore.SetSessionState to store the result.
func generateMessageKeys(
senderIdentity, recipientIdentity string,
senderIdentityPubkeyHash, recipientIdentityPubkeyHash string,
rootKey *[32]byte,
recipientKeys bool,
senderSessionPub, recipientPub *[32]byte,
numOfKeys uint64,
keyStore session.Store,
) error {
var (
identities string
send []string
recv []string
)
// identity_fix = HASH(SORT(SenderNym, RecipientNym))
if senderIdentity < recipientIdentity {
identities = senderIdentity + recipientIdentity
} else {
identities = recipientIdentity + senderIdentity
}
identityFix := cipher.SHA512([]byte(identities))
recipientPubHash := cipher.SHA512(recipientPub[:])
senderSessionPubHash := cipher.SHA512(senderSessionPub[:])
chainKey := rootKey[:]
for i := uint64(0); i < numOfKeys; i++ {
// messagekey_send[i] = HMAC_HASH(chainkey, "MESSAGE" | HASH(RecipientPub) | identity_fix)
buffer := append([]byte("MESSAGE"), recipientPubHash...)
buffer = append(buffer, identityFix...)
send = append(send, base64.Encode(cipher.HMAC(chainKey, buffer)))
// messagekey_recv[i] = HMAC_HASH(chainkey, "MESSAGE" | HASH(SenderSessionPub) | identity_fix)
buffer = append([]byte("MESSAGE"), senderSessionPubHash...)
buffer = append(buffer, identityFix...)
recv = append(recv, base64.Encode(cipher.HMAC(chainKey, buffer)))
// chainkey = HMAC_HASH(chainkey, "CHAIN" )
chainKey = cipher.HMAC(chainKey, []byte("CHAIN"))[:32]
}
// calculate root key hash
rootKeyHash := base64.Encode(cipher.SHA512(rootKey[:]))
bzero.Bytes(rootKey[:])
// reverse key material, if necessary
if recipientKeys {
send, recv = recv, send
}
// store session
var sessionKey string
if recipientKeys {
key := recipientIdentityPubkeyHash
key += senderIdentityPubkeyHash
key += base64.Encode(cipher.SHA512(recipientPub[:]))
key += base64.Encode(cipher.SHA512(senderSessionPub[:]))
sessionKey = base64.Encode(cipher.SHA512([]byte(key)))
} else {
key := senderIdentityPubkeyHash
key += recipientIdentityPubkeyHash
key += base64.Encode(cipher.SHA512(senderSessionPub[:]))
key += base64.Encode(cipher.SHA512(recipientPub[:]))
sessionKey = base64.Encode(cipher.SHA512([]byte(key)))
}
err := keyStore.StoreSession(sessionKey, rootKeyHash,
base64.Encode(chainKey), send, recv)
if err != nil {
return err
}
return nil
}