Transaction exchange process in Lightning Network

[user512]

Hello,
how is ensured that secret and new commitment transaction exchange take place at the same time? If for example Alice sends Bob the new commitment transaction only if he sends her a secret for penalization transaction activation, and she lies, it can end by balance freeze forever, because at now Alice has secret and Bob has nothing, so Bob can't send a transaction to blockchain (if he does it, Alice uses his secret to take all his money from the channel) and Alice does not do it because she wants Bob broke even if her money are freezed too.

[achow101]

If for example Alice sends Bob the new commitment transaction only if he sends her a secret for penalization transaction activation, and she lies

The secret is sent in response to the new commitment, not the other way around. The new commitment is committed to first before the previous commitment is revoked. Otherwise you run into this issue. There is nothing that prevents this except for the fact that the protocol specifies that commitments must be sent first. So compliant software will wait for the commitment to be sent before they send the secret.