Check password with RegEx

Hi everyone,
I am new to regular expressions and am working on a
"check password"
method using regex.

I have managed to create all checks in regular expressions
except the
following two:
 * First n characters should not contain the name (e.g. if
name is
"Peter" and we specify that name cannot be in
the first 8 characters,
then the text "12Peter2123fr" should validate
false).
 * Text should contain at least 1 lowercase char, 1
uppercase char, 1
number and 1 special char (!£$%&*#+-<>).

Can anyone help me with this?

Thanks,
David


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how would u define 'name'? What chars constitute 'name'?
what is the
pattern for it? Until u know the rule(s) for 'name' u
cannot start
coding that constraint for the password..


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Hi Sergei,
Name is a Windows username e.g. the name the user types in
when trying
to logon to a computer. Generally I guess it would be a
string of chars
e.g. "David", "Dav",
"de" etc. so that string in the exact order
should
not be in the n first chars of the password...

/David

Sergei Z wrote:
> how would u define 'name'? What chars constitute
'name'? what is the
> pattern for it? Until u know the rule(s) for 'name' u
cannot start
> coding that constraint for the password..


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David Eliasen wrote:
> Hi everyone,
> I am new to regular expressions and am working on a
"check password"
> method using regex.
>
> I have managed to create all checks in regular
expressions except the
> following two:
>  * First n characters should not contain the name (e.g.
if name is
> "Peter" and we specify that name cannot be
in the first 8 characters,
> then the text "12Peter2123fr" should
validate false).
>  * Text should contain at least 1 lowercase char, 1
uppercase char, 1
> number and 1 special char (!£$%&*#+-<>).
>
> Can anyone help me with this?
>
> Thanks,
> David

First requirement is tricky: it requires a nested
look-ahead/look-behind to implement:

this regex

^(?!.(?<=Peter.*?).).{1,55}$

will do the job, it will not allow 'Peter' to be within
the first 8
chars of the password.

second req is trivial: u simply apply 4 look aheads in a row
: one for
each group of chars. The regex for both reqs is:

^(?-i)(?!.(?<=Peter.*?).)(?=.*?[a-z])(?=.*?[A-Z])(?=.*
?\d)(?=.*?[£$%&*#+<>).-]).{1,55}$

it'll validate:

vvvvPeter2123frvvvv.vv

it'll fail on:

vvvPeter2123frvvvv.vv

WArning: looks at option swith (?-i) : it is .NET specific
syntax for
turning OFF Ignore case mode; in your environment u might
change the
syntax accordingly. Anyway I tested it in
http://regexlib.com
/RETester.aspx, and it works according to your spec.


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forgot to tell u (i guess it's obvious) that the regex will
have to be
created on the fly, after the user inputs a userid. You know
it, I'm
sure.


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David Eliasen wrote:
> Hi everyone,
> I am new to regular expressions and am working on a
"check password"
> method using regex.
>
> I have managed to create all checks in regular
expressions except the
> following two:
>  * First n characters should not contain the name (e.g.
if name is
> "Peter" and we specify that name cannot be
in the first 8 characters,
> then the text "12Peter2123fr" should
validate false).

what's the language/tool you are using? Is the 'name'
field known or
generated on the fly??

If you can use Perl, you can do things like:
=======
my $str = '12Peter2123fr';
my $first_n_char = 8;
my $name = 'Peter';
my $len = $first_n_char - length($name);
print "Matched\n" if $str =~
/^(?!.{0,$len}$name)/;

In another word, if you know the 'name' field is 'Peter'
which has
exactly 5 characters, then the pattern is like:

    ^(?!.{0,3}Peter)

>  * Text should contain at least 1 lowercase char, 1
uppercase char, 1
> number and 1 special char (!£$%&*#+-<>).

This part is pretty much like an FAQ in this group, 

 
(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[!£\$%&*#+<>-
])

so, by grouping both requirements, your pattern can be like:

   
^(?!.{0,3}Peter)(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[!£\$%&
amp;*#+<>-])

Regards,
Xicheng


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Xicheng,

thanks for posting the solution. U always seem to find the
easiest
solutuions possible: my nested look-behind was clearly an
overkill ;=).


See u around,

Sergei


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