allow older version of ssh-keygen

show_fingerprints.pl

@@ -12,6 +12,9 @@
 
 use strict;
 
+my ($version, $has_E)= get_ssh_version();
+my $hash_algorithm= 'MD5';
+
 my @files= <*.pub>;
 # print "files: ", join (' ', @files), "\n";
 push (@files, <authorized_keys*>);
@@ -19,7 +22,10 @@ push (@files, <authorized_keys*>);
 printf ("%-20s %5s %-51s %-6s %s\n", qw(file size fingerprint type notes));
 foreach my $file (@files)
 {
-  my @cmd= (qw(ssh-keygen -lE md5 -f), $file);
+  my @cmd= qw(ssh-keygen -l);
+  push (@cmd, '-E', $hash_algorithm) if ($has_E);
+  push (@cmd, '-f', $file);
+
   my $res= `@cmd`;
   my @lines= split ("\n", $res);
   foreach my $line (@lines)
@@ -28,9 +34,28 @@ foreach my $file (@files)
 
     my $type= 'unknown';
     if ($notes =~ m#(.+)\s+\((.+)\)#) { ($notes, $type)= ($1, $2) }
+    $fp= join(':', $hash_algorithm, $fp) unless ($has_E);
+
+    printf ("%-20s %5d %-51s %-6s %s\n", $file, $size, $fp, $type, $notes);
+  }
+}
 
-    printf ("%-20s %5d %s %-6s %s\n", $file, $size, $fp, $type, $notes);
+sub get_ssh_version
+{
+  my @cmd= qw(ssh-keygen --version); # apparently, there is way to display the version directly
+  my $res= `@cmd 2>&1`;
+
+  my $version= 'unknown';
+  my $has_E= 0;
+  foreach my $l (split ("\n", $res))
+  {
+    # print "[$l]\n";
+
+       if ($l =~ '  -L          Print the contents of a certificate.') { $has_E= 0; }
+    elsif ($l eq '       ssh-keygen -l [-v] [-E fingerprint_hash] [-f input_keyfile]') { $has_E= 1; }
   }
+
+  ($version, $has_E);
 }
 
 =head1 TODO