SQL Server 2014

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create table test 
(
  id int identity(1,1) primary key,
  col varchar(42)
);
insert into test (col) values
(N'HELLO 0123'),
(N'01234>56789'),
(N'abcdefghijklm#nopqrstuvwxyz'),
(N'ABCDEFGHIJKLM^NOPQRSTUVWXYZ'),
(null);
5 rows affected

--
-- Temporary tally table with numbers
-- Will be used to unfold that characters
--
if object_id('tempdb..#nums') is not null
  drop table #nums;
    
create table #nums (n int primary key);

with rcte as
(
 select 1 n, max(len(col)) max_n
 from test
 
 union all
 
 select n+1, max_n
 from rcte 
 where n <= max_n
)
insert #nums (n)
select n 
from rcte
option (maxrecursion 4000);
Warning: Null value is eliminated by an aggregate or other SET operation.
28 rows affected

select t.*, a.scramble
from test t
outer apply
(
  select q.x.value('.', 'VARCHAR(MAX)') as scramble
  from
  (
    select
     case 
     when substring(col,n,1) between '0' and '9'
     then substring(
      '5678901234',charindex(substring(col,n,1),
      '0123456789'),1)
     when ascii(substring(col,n,1)) between ascii('a') and ascii('z')
     then substring(
      'nomrqputswvyzxiacbedghfjlk',charindex(substring(col,n,1),
      'abcdefghijklmnopqrstuvwxyz'),1)
     when ascii(substring(col,n,1)) between ascii('A') and ascii('Z')
     then substring(
      'NOMRQPUTSWVYZXIACBEDGHFJLK',charindex(substring(col,n,1),
      'ABCDEFGHIJKLMNOPQRSTUVWXYZ'),1)
     else substring(col,n,1)
     end
    from #nums
    where n between 1 and len(col)
    order by n
    for xml path (''), type
  ) q(x)
  where q.x is not null
) a;


id
col
scramble


1
HELLO 0123
TQYYI 5678

2
01234>56789
56789>01234

3
abcdefghijklm#nopqrstuvwxyz
nomrqputswvyz#xiacbedghfjlk

4
ABCDEFGHIJKLM^NOPQRSTUVWXYZ
NOMRQPUTSWVYZ^XIACBEDGHFJLK

5
null
null


--
-- Rotation scramble
--
select t.*, a.scramble
from test t
outer apply
(
  select q.x.value('.', 'VARCHAR(MAX)') as scramble
  from
  (
    select 
    case
    when substring(col,n,1) between '0' and '9'
    then char(ascii('0')+(ascii(substring(col,n,1))-ascii('0')+5)%10)
    when ascii(substring(col,n,1)) between ascii('a') and ascii('z')
    then char(ascii('a')+(ascii(substring(col,n,1))-ascii('a')+13)%26)
    when ascii(substring(col,n,1)) between ascii('A') and ascii('Z')
    then char(ascii('A')+(ascii(substring(col,n,1))-ascii('A')+13)%26)
    else substring(col,n,1)
    end
    from #nums
    where n between 1 and len(col)
    order by n
    for xml path (''), type
  ) q(x)
) a


id
col
scramble


1
HELLO 0123
URYYB 5678

2
01234>56789
56789>01234

3
abcdefghijklm#nopqrstuvwxyz
nopqrstuvwxyz#abcdefghijklm

4
ABCDEFGHIJKLM^NOPQRSTUVWXYZ
NOPQRSTUVWXYZ^ABCDEFGHIJKLM

5
null
null

id	col	scramble
1	HELLO 0123	TQYYI 5678
2	01234>56789	56789>01234
3	abcdefghijklm#nopqrstuvwxyz	nomrqputswvyz#xiacbedghfjlk
4	ABCDEFGHIJKLM^NOPQRSTUVWXYZ	NOMRQPUTSWVYZ^XIACBEDGHFJLK
5	null	null

id	col	scramble
1	HELLO 0123	URYYB 5678
2	01234>56789	56789>01234
3	abcdefghijklm#nopqrstuvwxyz	nopqrstuvwxyz#abcdefghijklm
4	ABCDEFGHIJKLM^NOPQRSTUVWXYZ	NOPQRSTUVWXYZ^ABCDEFGHIJKLM
5	null	null