With the methods of the Base module, you can pass which case you want the
output string to be encoded in. Default is upper, but lower can be achieved
without String.downcase/1:
iex(1)> bytes = :crypto.strong_rand_bytes(32)
<<10, 172, 2, 91, 154, 240, 89, 162, 143, 96, 28, 69, 174,
179, 223, 221, 232, 248, 28, 193, 159, 57, 142, 148, 188,
215, 14, 42, 69, 35, 225, 48>>
iex(2)> bytes |> Base.encode16()
"0AAC025B9AF059A28F601C45AEB3DFDDE8F81CC19F398E94BCD70E2A4523E130"
iex(3)> bytes |> Base.encode16(case: :lower)
"0aac025b9af059a28f601c45aeb3dfdde8f81cc19f398e94bcd70e2a4523e130"