SilcBool silc_cipher_set_key(SilcCipher cipher, const unsigned char *key,
                                 SilcUInt32 keylen, SilcBool encryption);

    Sets the key for the cipher.  The `keylen' is the key length in
    bits.  If the `encryption' is TRUE the key is for encryption, if FALSE
    the key is for decryption.