view release on metacpan or  search on metacpan

lib/Apache/AppSamurai/Util.pm  view on Meta::CPAN

 print $msg, "\n";
 # Prints out: Who stole my notebookXXXXXXXXXXXXXXXXXXXX

=head1 DESCRIPTION

This is a set of utility methods for L<Apache::AppSamurai|Apache::AppSamurai>
and related sub-modules to use.  All methods should be called with a full
module path, (Apache::AppSamurai::Util::CheckHostIp(), etc), or be imported
into the current namespace.

Almost all the methods return a clean, untainted value on success, or undef
on failure.

=head1 METHODS

=head2 expires()

Convert a UNIX timestamp to a valid cookie expire stamp.  (Copied from
L<CGI::Util|CGI::Util>).

=head2 CreateSessionAuthKey()

Takes one or more arguments and concatenates them.  If no arguments are given,
a random string is created instead.  Returns the SHA256 digest hex string 
of the input or random string.

=head2 HashPass()

Takes a scalar with printable text (normal chars and whitespace), and returns
the SHA256 digest hex string of the input.

=head2 HashAny()

Concatenates one or more arguments and returns the SHA256 digest hex string
of the input.  This method allows an input of ''.  Do not use for security
checks without first checking your input.

=head2 ComputeSessionId()

Takes a session authentication key, (generally the cookie value from the
client), as the first argument.  The second is the server key, (configured
with the ServerKey or ServerPass option in the Apache config.)  After checking
for valid input, a HMAC is calculated using the SHA256 digest algorithm.
The HMAC is returned as a hex string.

This method of looking up the real (local) session ID allows for keeping the
session authentication key a secret to the web server while it is not
being actively used.  This is important because the session authentication key
is used (in part) to encrypt the user's session data.  Without the session
authentication key, a hacker can not steal information from a stale session
file, remnant data on a hard drive, or from a hacked database.

=head2 CheckSidFormat()

Check input scalar for proper ID format.  (Characters and length.)  Returns
the untainted input, or undef on failure.

Apache::AppSamurai currently uses SHA256 for all digest and ID functions.
All are represented as hex strings with a length of 32 characters.  (256 bits
divided by 4 characters per nibble.)  This magic number is set in the C<$IDLEN>
global in the Util.pm file.  Future versions may be more flexible and allow
alternate digest algorithms.

=head2 CheckUrlFormat()

Check the scalar for proper URL formatting.  Returns the untainted URL or undef
on failure.

This is just a basic check, and allows through ftp:, gopher:, etc in addition
to http: and https:.  It is just a sanity check.  Apply more extensive
filtering using mod_rewrite or other means, as needed.

=head2 CheckHostName()

Check scalar for basic hostname/domain name syntax.  Returns an untainted
version of the input, or undef on failure.

=head2 CheckHostIP()

Check input scalar for proper text IP format. Returns the untainted input
on success, or undef on failure.

IPv4 dotted quads are only supported at this time.  IPv6 support will be
added, but considering the ungodly tangled mess that can represent an
IPv6 address, the motivation to tackle it is not currently present.

=head2 XHalf()

Check that input scalar is text, then convert the second half of the string
to a string of 'X's and return the new string.

This is used for debug logging of potentially sensitive information, where
some context text is required, but where a full disclosure would be dangerous.
Only use this method when the latter half of the text contains all or most
of the sensitive data.  It is a convenience function to avoid needing to
write custom data sanitization into each logging event.

For instance, for a session ID of
"628b49d96dcde97a430dd4f597705899e09a968f793491e4b704cae33a40dc02"
the output would be:
"628b49d96dcde97a430dd4f597705899XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
which would be fairly safe since only half the data would be revealed in the
log. This is still 128 bits of digest, and in most cases would be enough not
to seriously endanger the data.
 
On the other hand, if you allow long passwords and you log a basic
authentication "Authorization:" header of:
"cm9nZXJ0aGVtYW46VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wZWQgb3ZlciB0aGUgbGF6eSBkb2cu"
the output would be:
"cm9nZXJ0aGVtYW46VGhlIHF1aWNrIGJyb3duIGXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX".
This is not very safe.  Here is what decoding produces:
"rogertheman:The quick brown e×]u×]u×]u×]u×]u×]u×]u×]u×]u×"
So, the user's name is "rogertheman".  More importantly, we can guess what
the rest of the password is, and we know the length of the password.

Apache::AppSamurai does log the Authorization: header using XHalf when
Debug is enabled.  Be very careful when running production servers!  Only
use Debug when absolutely needed, monitor the logs for sensitive information
leak, and remove debug log data when possible.

That said, leave Debug set to 0 and do not use XHalf in any modules you