DBMS_CRYPTO.ENCRYPT_AES128

DECLARE
  ENC_VAL   RAW (2000);
  L_KEY     RAW (2000);
  L_KEY_LEN NUMBER := 128;
  L_MOD     NUMBER := DBMS_CRYPTO.ENCRYPT_AES128 + 
                      DBMS_CRYPTO.CHAIN_CBC      +
                      DBMS_CRYPTO.PAD_PKCS5;
BEGIN
  L_KEY   := DBMS_CRYPTO.RANDOMBYTES (L_KEY_LEN);
  ENC_VAL := DBMS_CRYPTO.ENCRYPT
                                (
                                 UTL_I18N.STRING_TO_RAW ('SECRET', 'AL32UTF8'),
                                 L_MOD,
                                 L_KEY
                                );
END;