保密工艺

其私家招牌菜鲨鱼丸由其独门绝密配方，通过十几道工序精心密制而成。

keep sth. a secret from sb.

lock a secret in one's heart

Lanshi Micang; Secret Book of Orchid Chamber

secret compartment

private ledger【会计】;secret ledger【会计】

let sb. into a secret

secret ballot

secret recipe