So here's a means of generating a random variation of the standard alphabet, eg

SQL> set serverout on
SQL> declare
  2    type rand_list is table of varchar2(62) index by pls_integer;
  3    source varchar2(62) := 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  4    perms  rand_list;
  5    source_variant varchar2(62);
  6  begin
  7    for i in 1 .. 1 loop
  8      source_variant := null;
  9      for j in ( select rownum r from dual connect by level <= 52 order by dbms_random.value )
 10      loop
 11        source_variant := source_variant || substr(source,j.r,1);
 12      end loop;
 13      for j in ( select rownum r from dual connect by level <= 10 order by dbms_random.value )
 14      loop
 15        source_variant := source_variant || substr(source,52+j.r,1);
 16      end loop;
 17      perms(i) := source_variant;
 18      dbms_output.put_line(source_variant);
 19    end loop;
 20  end;
 21  /
vPXGlJNLVUcEChAeFfRpgWmtwodZBiurSsDOyKkQHTnbzYaMIjxq8053421796

So you can see we randomised:

ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789

to

vPXGlJNLVUcEChAeFfRpgWmtwodZBiurSsDOyKkQHTnbzYaMIjxq8053421796

The reason that is useful is that we can now do:

translate(some_string,
     'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789',
     'vPXGlJNLVUcEChAeFfRpgWmtwodZBiurSsDOyKkQHTnbzYaMIjxq8053421796')

to randomise a string in the way you want.

If you want to do this to LOTS of strings, then obviously this simple mapping is easy to crack - this might be want to you want, it might not be...You can adjust the 'i' loop above to generate more then one, eg

SQL> declare
  2    type rand_list is table of varchar2(62) index by pls_integer;
  3    source varchar2(62) := 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  4    perms  rand_list;
  5    source_variant varchar2(62);
  6  begin
  7    for i in 1 .. 10 loop
  8      source_variant := null;
  9      for j in ( select rownum r from dual connect by level <= 52 order by dbms_random.value )
 10      loop
 11        source_variant := source_variant || substr(source,j.r,1);
 12      end loop;
 13      for j in ( select rownum r from dual connect by level <= 10 order by dbms_random.value )
 14      loop
 15        source_variant := source_variant || substr(source,52+j.r,1);
 16      end loop;
 17      perms(i) := source_variant;
 18      dbms_output.put_line(source_variant);
 19    end loop;
 20  end;
 21  /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These are all being stored in an array called 'perms'. So now you can pick one of *these* at random, eg

translate(some_string,
     'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789',
     perms(trunc(dbms_random.value(1,10.99)))
     )

So it will perform a random translation with subsequent execution. You could have 100's of such permutations.