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mitigate timing attacks by taking no shortcuts #6

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mitigate timing attacks by taking no shortcuts #6

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25 changes: 24 additions & 1 deletion lib/Crypt/PBKDF2.pm
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Original file line number Diff line number Diff line change
Expand Up @@ -222,6 +222,27 @@ method can produce.

=cut

# no-shortcut version of eq
sub _is_equal {
my ($x, $y) = @_;

my $length_check = length($x) == length($y);

my $result = 0;
my @x = split //, $x;
my @y = split //, $y;
for my $char_x (@x) {
my $char_y = shift @y;
{
no warnings "uninitialized";
$result |= ord($char_x) ^ ord($char_y);
}
}
my $eq_check = $result == 0;

return $length_check & $eq_check;
}

sub validate {
my ($self, $hashed, $password) = @_;

Expand All @@ -246,7 +267,9 @@ sub validate {

my $check_hash = $checker->PBKDF2($info->{salt}, $password);

return ($check_hash eq $info->{hash});
# help mitigate timing attacks by taking no shortcuts when comparing
# two hashes (eq will stop when they are no longer equal)
return _is_equal($check_hash, $info->{hash});
}

=method PBKDF2 ($salt, $password)
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