tsec.cipher.symmetric
https://tools.ietf.org/html/rfc7539#section-2.5 impl derived from: https://cr.yp.to/snuffle/xsalsa-20081128.pdf https://github.com/jedisct1/libsodium/blob/master/src/libsodium/crypto_secretbox/xsalsa20poly1305/secretbox_xsalsa20poly1305.c