use Tempdb
go
if object_ID('fn_ACITEncryption') is not null
    drop function fn_ACITEncryption
go
create function fn_ACITEncryption
(
    @Str nvarchar(4000),--加密的字符串
    @Flag bit=1,--1、加密 0、解密
    @Key nvarchar(50)--密文
)
returns nvarchar(4000)--這里可轉換成二進制
with Encryption
as
begin
Declare @LenStr int,@i int,@Str2 nvarchar(4000),@Split nvarchar(2),@LenKey int
select @Str=@Str+'A',@LenStr=len(@Str),@i=1,@Str2='',@LenKey=Len(@Key+'A')-1
while @i<@LenStr
        select    @Split=substring(@Str,@i,1),
                @Split=nchar((unicode(@Split)+case @Flag    when 1 then unicode(substring(@Key+'A',@i%@LenKey+1,1))-1                                                
                                                    when 0 then 65535-unicode(substring(@Key+'A',@i%@LenKey+1,1))
                                                    else 0 end)%65535+cast(@Flag as int)),
                @Str2=@Str2+@Split,@i=@i+1
return @Str2

end
go
select dbo.fn_ACITEncryption(N'Roy',1,'123') as 加密后字符串

/*
加密后字符串
------------------------------
?¢ª

(1 個資料列受到影響)

*/
select dbo.fn_ACITEncryption(N'?¢ª',0,'123') as 解密后字符串
/*
解密后字符串
--------------------------
Roy

(1 個資料列受到影響)
*/