use Crypt::CBC; my $cipher = Crypt::CBC->new(...); open(INFILE, '<', 'BIG_FILE.enc') or die("Unable to open input file: $!"); open(OUTFILE, '>', 'BIG_FILE.txt') or die("Unable to create output file: $!"); $cipher->start('decrypting'); while (read(INFILE, $buffer, 65536)) { print OUTFILE $cipher->crypt($buffer); } print OUTFILE $cipher->finish;