How to set a 24 byte length key to elixir/erlang block_encrypt/4 function using des_ede3 as mode of encryption

问题

Am trying to send data to an external api that expects encrypted data using 3DES encryption but am having issues understanding how to pass my api key as the key field to erlangs des_ede3 cipher.

According to erlangs cipher docs des_ede3 expects 3 keys that are all 8 bytes in length. How can i pass my 24 byte api key as the key to elixir/erlang :cryptoblock_encrypt/4 function

*** how can i pass key to block_encrypt/4 ***
key = "123456789012345678901234"
data = "hello world! The world is yours"
block_size = 8
cipher = :crypto.block_encrypt(:des_ede3, [key, key, key], iv, pad(data, block_size))

How do i pass my 24 byte api key as the key to erlangs block_encrypt/4 in order for me to pass data to the external api.

Thanks

回答1:

Use binary pattern matching:

<<k1 :: binary-size(8),
  k2 :: binary-size(8),
  k3 :: binary-size(8)>> = "123456789012345678901234"
#⇒ "123456789012345678901234"

{k1, k2, k3}
#⇒ {"12345678", "90123456", "78901234"}

来源：https://stackoverflow.com/questions/57478114/how-to-set-a-24-byte-length-key-to-elixir-erlang-block-encrypt-4-function-using