SCOTT@orcl_12.1.0.2.0> CREATE TABLE scrambled
  2    (DATE_OF_BIRTH  DATE,
  3  	FIRST_NAME	 VARCHAR2(20),
  4  	POSTCODE	 NUMBER(8))
  5  /

Table created.

SCOTT@orcl_12.1.0.2.0> INSERT INTO scrambled (date_of_birth, first_name, postcode)
  2  SELECT SYSDATE - DBMS_RANDOM.VALUE (1,366),
  3  	    DBMS_RANDOM.STRING ('U', 20),
  4  	    LPAD (CEIL (DBMS_RANDOM.VALUE (1,99999999)), 8, '0')
  5  FROM   DUAL
  6  CONNECT BY LEVEL <= 10
  7  /

10 rows created.

SCOTT@orcl_12.1.0.2.0> SELECT date_of_birth, first_name, postcode
  2  FROM   scrambled
  3  /

DATE_OF_BIRTH   FIRST_NAME             POSTCODE
--------------- -------------------- ----------
Wed 17-Aug-2016 RVRGBSLRWWJRQJBEGCLV   49870953
Thu 18-Feb-2016 GAUERUCEJVWPVBRYOBKO   57185556
Wed 10-Aug-2016 YCYYYLLAHOLLZJBEWVNS   47283027
Sat 22-Oct-2016 SHIPGRRAGLZFZSPDVKSU   29099732
Sat 12-Mar-2016 YXFNUBUXUHSHSFPPLRMH   75059706
Mon 15-Aug-2016 EOMXOPQUOLDYVDRBOLHY   74212704
Mon 02-May-2016 KOIBUHRMFLKLUUDKWIIX   23236438
Fri 01-Jul-2016 KJGDBTPFZDYMPGEGBVGY   86288842
Tue 09-Feb-2016 SYOOJWJOMEBQRKUKNQPE   95729329
Tue 12-Jan-2016 RZAFGDHEVYMZYQZLHBJB   76658230

10 rows selected.

UPDATE customers
   SET cust_email =
             DBMS_RANDOM.string ('l',
                                 LENGTH (REGEXP_SUBSTR (cust_email,
                                                        '[A-Z][a-z]+',
                                                        1,
                                                        1)))
          || '.'
          || DBMS_RANDOM.string ('l',
                                LENGTH (REGEXP_SUBSTR (cust_email,
                                                        '[A-Z][a-z]+',
                                                        1,
                                                       2)))
          || '@'
          || DBMS_RANDOM.string ('l',
                                 LENGTH (REGEXP_SUBSTR (cust_email,
                                                      '[A-Z][a-z]+',
                                                       1,
                                                     1)))
          || '.'
          ||DBMS_RANDOM.string('l',3)
 WHERE cust_email IS NOT NULL;
/

SELECT CUST_EMAIL,
          TRANSLATE(CUST_EMAIL,REPLACE(REPLACE(CUST_EMAIL,'.'),'@'),DBMS_RANDOM.String ('U', LENGTH(CUST_EMAIL)))
           Altered_email
  FROM CUSTOMERS
 WHERE CUST_Email is not null;

SELECT CUST_EMAIL,
          SCRAMBLE_STR(CUST_EMAIL,'.@') Altered_email
  FROM CUSTOMERS
 WHERE CUST_Email is not null;

CREATE OR REPLACE FUNCTION Scramble_str (P_str      IN VARCHAR2,
                                         P_filter   IN VARCHAR2 DEFAULT NULL)
    RETURN VARCHAR2
IS
    P_return   VARCHAR2 (1000);
    Flag       VARCHAR2 (1);
BEGIN
    P_return := NULL;

    IF P_str IS NOT NULL
    THEN
        Flag := 'N';

        FOR Pnt IN 1 .. LENGTH (P_str)
        LOOP
            IF P_filter IS NOT NULL
            THEN
                FOR Pnt2 IN 1 .. LENGTH (P_filter)
                LOOP
                    IF SUBSTR (P_str, Pnt, 1) = SUBSTR (P_filter, Pnt2, 1)
                    THEN
                        IF P_return IS NULL
                        THEN
                            P_return := SUBSTR (P_str, Pnt, 1);
                        ELSE
                            P_return := P_return || SUBSTR (P_str, Pnt, 1);
                        END IF;

                        Flag := 'Y';
                        EXIT;
                    END IF;
                END LOOP;
            END IF;

            IF Flag = 'N'
            THEN
                IF ASCII (SUBSTR (P_str, Pnt, 1)) NOT BETWEEN 97 AND 122
                THEN
                    IF P_return IS NULL
                    THEN
                        P_return := DBMS_RANDOM.String ('U', 1);
                    ELSE
                        P_return := P_return || DBMS_RANDOM.String ('U', 1);
                    END IF;
                ELSIF ASCII (SUBSTR (P_str, Pnt, 1)) BETWEEN 97 AND 122
                THEN
                    IF P_return IS NULL
                    THEN
                        P_return := DBMS_RANDOM.String ('L', 1);
                    ELSE
                        P_return := P_return || DBMS_RANDOM.String ('L', 1);
                    END IF;
                ELSE
                    IF P_return IS NULL
                    THEN
                        P_return := SUBSTR (P_str, Pnt, 1);
                    ELSE
                        P_return := P_return || SUBSTR (P_str, Pnt, 1);
                    END IF;
                END IF;
            END IF;

            Flag := 'N';
        END LOOP;
    END IF;

    RETURN P_return;
END Scramble_str;