Bug#700617: Digest::HMAC->new () is "incompatible" with Digest::SHA (512)

[Ivan Shmakov]

Package: libdigest-hmac-perl
Version: 1.03+dfsg-1
Tags: patch

        It isn't currently possible to use the Digest::HMAC module's OO
        interface along with the Digest subclasses whose constructors
        require an argument, such as the Digest::SHA class (as provided
        by the libdigest-sha-perl package) or Digest->new () itself.

        The patch MIME'd provides a way for the caller to pass a
        prepared Digest instance, which is then clone ()'d and reset ()
        to produce a “clean” Digest object.

        Examples:

   require Digest::HMAC;
   require Digest::SHA;

   my $hmac
       = Digest::HMAC->new ($key, Digest::SHA->new (256));
   ## check, e. g., [1]
   my $hmac
       = Digest::HMAC->new ($key, Digest::SHA->new (384), 128);
   my $hmac
       = Digest::HMAC->new ($key, Digest::SHA->new (512), 128);

        FWIW, I've tested HMAC-SHA512 by making DNS updates to
        BIND9-hosted zones with Net::DNS.

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=313196

-- 
FSF associate member #7257

--- HMAC.pm	2011-07-25 16:51:15.000000000 +0000
+++ HMAC.pm	2013-02-15 08:55:09.000000000 +0000
@@ -9,12 +9,16 @@
 {
     my($class, $key, $hasher, $block_size) =  @_;
     $block_size ||= 64;
-    $key = $hasher->new->add($key)->digest if length($key) > $block_size;
+    my $d
+        = (ref($hasher) eq ""
+           ? $hasher->new()
+           : $hasher->clone()->reset());
+    $key = $d->add($key)->digest if length($key) > $block_size;
 
     my $self = bless {}, $class;
     $self->{k_ipad} = $key ^ (chr(0x36) x $block_size);
     $self->{k_opad} = $key ^ (chr(0x5c) x $block_size);
-    $self->{hasher} = $hasher->new->add($self->{k_ipad});
+    $self->{hasher} = $d->add($self->{k_ipad});
     $self;
 }
 
@@ -79,6 +83,7 @@
  # OO style
  use Digest::HMAC;
  $hmac = Digest::HMAC->new($key, "Digest::MyHash");
+ $hmac = Digest::HMAC->new($key, Digest::MyHash->new());
 
  $hmac->add($data);
  $hmac->addfile(*FILE);