key_len=

        # OpenSSL::Cipher.key_len=

(from ruby core)
### Implementation from Cipher
---
    cipher.key_len = integer -> integer

---

Sets the key length of the cipher.  If the cipher is a fixed length
cipher then attempting to set the key length to any value other than the
fixed value is an error.

Under normal circumstances you do not need to call this method (and
probably shouldn't).

See EVP_CIPHER_CTX_set_key_length for further information.