Salsa20 family of encryption functions, in pure OCaml

utop[0]> #require "mirage-crypto";;
utop[1]> #require "mirage-crypto-rng.unix";;
utop[2]> Mirage_crypto_rng_unix.initialize ();;
- : unit = ()
utop[3]> let key = Mirage_crypto_rng.generate 32;;
val key : Cstruct.t = {Cstruct.buffer = <abstr>; off = 0; len = 32}
utop[4]> let nonce = Cstruct.create 8;;
val nonce : Cstruct.t = {Cstruct.buffer = <abstr>; off = 0; len = 8}
utop[5]> #require "salsa20";;
utop[6]> let state = Salsa20.create key nonce;;
val state : Salsa20.t = <abstr>
utop[7]> Salsa20.encrypt (Cstruct.of_string "My secret text") state |> Cstruct.to_string;;
- : string = " 2\193\020`\142\182\234\188H[R\241V"