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This module is in alpha-testing. Build in the usual way; send bug reports
and patches to me at the address below. From the documentation:
NAME
Term::ReadPassword - Asking the user for a password
SYNOPSIS
use Term::ReadPassword;
while (1) {
my $password = read_password('password: ');
redo unless defined $password;
if ($password eq 'flubber') {
print "Access granted.\n";
last;
} else {
print "Access denied.\n";
redo;
}
}
DESCRIPTION
This module lets you ask the user for a password in the
traditional way, from the keyboard, without echoing.
This is not intended for use over the web; user authentication
over the web is another matter entirely. Also, this module
should generally be used in conjunction with Perl's crypt()
function, sold separately.
The read_password function prompts for input, reads a line of
text from the keyboard, then returns that line to the caller.
The line of text doesn't include the newline character, so
there's no need to use chomp.
While the user is entering the text, a few special characters
are processed. The character delete (or the character backspace)
will back up one character, removing the last character in the
input buffer (if any). The character CR (or the character LF)
will signal the end of input, causing the accumulated input
buffer to be returned. And, optionally, the character Control-C
may be used to terminate the input operation. (See details
below.) All other characters, even ones which would normally
have special purposes, will be added to the input buffer.
It is not recommended, though, that you use the as-yet-
unspecified control characters in your passwords, as those
characters may become meaningful in a future version of this
module. Applications which allow the user to set their own
passwords may wish to enforce this rule, perhaps with code
something like this:
{
# Naked block for scoping and redo
my $new_pw = read_password("Enter your new password: ");
if ($new_pw =~ /([^\x20-\x7E])/) {
my $bad = unpack "H*", $1;
print "Your password may not contain the ";
print "character with hex code $bad.\n";
redo;
} elsif (length($new_pw) < 5) {
print "Your password must be longer than that!\n";
redo;
} elsif ($new_pw ne read_password("Enter it again: ")) {
print "Passwords don't match.\n";
redo;
} else {
&change_password($new_pw);
print "Your password is now changed.\n";
}
}
The second parameter to read_password is the optional
`idle_timeout' value. If it is a non-zero number and there is no
keyboard input for that many seconds, the input operation will
terminate. Notice that this is not an overall time limit, as the
timer is restarted with each new character.
The third parameter will optionally allow the input operation to
be terminated by the user with Control-C. If this is not
supplied, or is false, a typed Control-C will be entered into
the input buffer just as any other character. In that case,
there is no way from the keyboard to terminate the program while
it is waiting for input. (That is to say, the normal ability to
generate signals from the keyboard is suspended during the call
to read_password.)
If the input operation terminates early (either because the
idle_timeout was exceeded, or because a Control-C was enabled
and typed), the return value will be `undef'. In either case,
there is no way provided to discover what (if anything) was
typed before the early termination, or why the input operation
was terminated.
So as to discourage users from typing their passwords anywhere
except at the prompt, any input which has been "typed ahead"
before the prompt appears will be discarded. And whether the
input operation terminates normally or not, a newline character
will be printed, so that the cursor will not remain on the line
after the prompt.
SECURITY
You would think that a module dealing with passwords would be
full of security features. You'd think that, but you'd be wrong.
For example, perl provides no way to erase a piece of data from
memory. (It's easy to erase it so that it can't be accessed from
perl, but that's not the same thing as expunging it from the
actual memory.) If you've entered a password, even if the
variable that contained that password has been erased, it may be
possible for someone to find that password, in plaintext, in a
core dump. And that's just one potential security hole.
In short, if serious security is an issue, don't use this
module.
AUTHOR
Tom Phoenix <rootbeer@redcat.com>
SEE ALSO
Term::ReadLine, the "crypt" entry in the perlfunc manpage, and
your system's manpages for the low-level I/O operations used
here.
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