You could try to use the C cypher and fall back on the Perl one. Something like

my $cypher;

if (eval { require Crypt::Twofish }) {
   $cypher = 'Crypt::Twofish';
} elsif (eval { require Crypt::Twofish_PP }) {
   warn("Crypt::Twofish not found. Falling back to slower Crypt::Twofi
+sh_PP\n") if $DEBUG;
   $cypher = 'Crypt::Twofish_PP';
} else {
   die("Neither Crypt::Twofish nor Crypt::Twofish_PP was found. Aborti
+ng");
}
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or

my $cypher;

foreach (qw(
   Crypt::Twofish
   Crypt::Twofish_PP
)) {
   my $mod  = $_;
   my $file = $_;

   $file =~ s{::}{/}g;
   $file .= '.pm';

   if (eval { require $file }) {
      $cypher = $mod;
      last;
   }
}

die("No acceptable encryption algorithm found. Aborting")
   if not defined $cypher;
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