Currently, the nonces used in secret connection are 12 bytes / 96 bits and basically a big endian encoded counter:

For the sake of consistency (ChaCha20 is all little endian) it would be great to change the nonce encoding to little endian, too.

Additionally to that, a counter using a simple 64-bit (unsigned) integer should be sufficiently large. It will not overflow in practice and we should have rekeyed long before it happens.

We should then also encode the chunk size here using little endian, too.

Related discussion: tendermint/tmkms#38 (comment)

cc @tarcieri @ValarDragon