mk-ca-bundle.pl

#!/usr/bin/env perl
# ***************************************************************************
# *                                  _   _ ____  _
# *  Project                     ___| | | |  _ \| |
# *                             / __| | | | |_) | |
# *                            | (__| |_| |  _ <| |___
# *                             \___|\___/|_| \_\_____|
# *
# * Copyright (C) Daniel Stenberg, <[email protected]>, et al.
# *
# * This software is licensed as described in the file COPYING, which
# * you should have received as part of this distribution. The terms
# * are also available at https://curl.se/docs/copyright.html.
# *
# * You may opt to use, copy, modify, merge, publish, distribute and/or sell
# * copies of the Software, and permit persons to whom the Software is
# * furnished to do so, under the terms of the COPYING file.
# *
# * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
# * KIND, either express or implied.
# *
# * SPDX-License-Identifier: curl
# *
# ***************************************************************************
# This Perl script creates a fresh ca-bundle.crt file for use with libcurl.
# It downloads certdata.txt from Mozilla's source tree (see URL below),
# then parses certdata.txt and extracts CA Root Certificates into PEM format.
# These are then processed with the OpenSSL commandline tool to produce the
# final ca-bundle.crt file.
# The script is based on the parse-certs script written by Roland Krikava.
# This Perl script works on almost any platform since its only external
# dependency is the OpenSSL commandline tool for optional text listing.
# Hacked by Guenter Knauf.
#
use Encode;
use Getopt::Std;
use MIME::Base64;
use strict;
use warnings;
use vars qw($opt_b $opt_d $opt_f $opt_h $opt_i $opt_k $opt_l $opt_m $opt_n $opt_p $opt_q $opt_s $opt_t $opt_u $opt_v $opt_w);
use List::Util;
use Text::Wrap;
use Time::Local;
my $MOD_SHA = "Digest::SHA";
eval "require $MOD_SHA";
if($@) {
    $MOD_SHA = "Digest::SHA::PurePerl";
    eval "require $MOD_SHA";
}
eval "require LWP::UserAgent";

my %urls = (
    'autoland' => 'https://raw.githubusercontent.com/mozilla-firefox/firefox/refs/heads/autoland/security/nss/lib/ckfw/builtins/certdata.txt',
    'beta'    => 'https://raw.githubusercontent.com/mozilla-firefox/firefox/refs/heads/beta/security/nss/lib/ckfw/builtins/certdata.txt',
    'release' => 'https://raw.githubusercontent.com/mozilla-firefox/firefox/refs/heads/release/security/nss/lib/ckfw/builtins/certdata.txt',
);

$opt_d = 'release';

# If the OpenSSL commandline is not in search path you can configure it here!
my $openssl = 'openssl';

my $version = '1.29';

$opt_w = 76; # default base64 encoded lines length

# default cert types to include in the output (default is to include CAs which
# may issue SSL server certs)
my $default_mozilla_trust_purposes = "SERVER_AUTH";
my $default_mozilla_trust_levels = "TRUSTED_DELEGATOR";
$opt_p = $default_mozilla_trust_purposes . ":" . $default_mozilla_trust_levels;

my @valid_mozilla_trust_purposes = (
    "DIGITAL_SIGNATURE",
    "NON_REPUDIATION",
    "KEY_ENCIPHERMENT",
    "DATA_ENCIPHERMENT",
    "KEY_AGREEMENT",
    "KEY_CERT_SIGN",
    "CRL_SIGN",
    "SERVER_AUTH",
    "CLIENT_AUTH",
    "CODE_SIGNING",
    "EMAIL_PROTECTION",
    "IPSEC_END_SYSTEM",
    "IPSEC_TUNNEL",
    "IPSEC_USER",
    "TIME_STAMPING",
    "STEP_UP_APPROVED"
);

my @valid_mozilla_trust_levels = (
    "TRUSTED_DELEGATOR",    # CAs
    "NOT_TRUSTED",          # Don't trust these certs.
    "MUST_VERIFY_TRUST",    # This explicitly tells us that it ISN'T a CA but is
                            # otherwise ok. In other words, this should tell the
                            # app to ignore any other sources that claim this is
                            # a CA.
    "TRUSTED"               # This cert is trusted, but only for itself and not
                            # for delegates (i.e. it is not a CA).
);

my $default_signature_algorithms = $opt_s = "MD5";

my @valid_signature_algorithms = (
    "MD5",
    "SHA1",
    "SHA256",
    "SHA384",
    "SHA512"
);

$0 =~ s@.*(/|\\)@@;
$Getopt::Std::STANDARD_HELP_VERSION = 1;
getopts('bd:fhiklmnp:qs:tuvw:');

if(!defined($opt_d)) {
    # to make plain "-d" use not cause warnings, and actually still work
    $opt_d = 'release';
}

# Use predefined URL or else custom URL specified on command line.
my $url;
if(defined($urls{$opt_d})) {
    $url = $urls{$opt_d};
    if(!$opt_k && $url !~ /^https:\/\//i) {
        die "The URL for '$opt_d' is not HTTPS. Use -k to override (insecure).\n";
    }
}
else {
  $url = $opt_d;
}

if($opt_i) {
    print ("=" x 78 . "\n");
    print "Script Version                   : $version\n";
    print "Perl Version                     : $]\n";
    print "Operating System Name            : $^O\n";
    print "Getopt::Std.pm Version           : ${Getopt::Std::VERSION}\n";
    print "Encode::Encoding.pm Version      : ${Encode::Encoding::VERSION}\n";
    print "MIME::Base64.pm Version          : ${MIME::Base64::VERSION}\n";
    print "LWP::UserAgent.pm Version        : ${LWP::UserAgent::VERSION}\n" if($LWP::UserAgent::VERSION);
    print "LWP.pm Version                   : ${LWP::VERSION}\n" if($LWP::VERSION);
    print "Digest::SHA.pm Version           : ${Digest::SHA::VERSION}\n" if($Digest::SHA::VERSION);
    print "Digest::SHA::PurePerl.pm Version : ${Digest::SHA::PurePerl::VERSION}\n" if($Digest::SHA::PurePerl::VERSION);
    print ("=" x 78 . "\n");
}

sub warning_message() {
    if($opt_d =~ m/^risk$/i) { # Long Form Warning and Exit
        print "Warning: Use of this script may pose some risk:\n";
        print "\n";
        print "  1) If you use HTTP URLs they are subject to a man in the middle attack\n";
        print "  2) Default to 'release', but more recent updates may be found in other trees\n";
        print "  3) certdata.txt file format may change, lag time to update this script\n";
        print "  4) Generally unwise to blindly trust CAs without manual review & verification\n";
        print "  5) Mozilla apps use additional security checks aren't represented in certdata\n";
        print "  6) Use of this script will make a security engineer grind his teeth and\n";
        print "     swear at you.  ;)\n";
        exit;
    } else { # Short Form Warning
        print "Warning: Use of this script may pose some risk, -d risk for more details.\n";
    }
}

sub HELP_MESSAGE() {
    print "Usage:\t${0} [-b] [-d<certdata>] [-f] [-i] [-k] [-l] [-n] [-p<purposes:levels>] [-q] [-s<algorithms>] [-t] [-u] [-v] [-w<l>] [<outputfile>]\n";
    print "\t-b\tbackup an existing version of ca-bundle.crt\n";
    print "\t-d\tspecify Mozilla tree to pull certdata.txt or custom URL\n";
    print "\t\t  Valid names are:\n";
    print "\t\t    ", join( ", ", map { ( $_ =~ m/$opt_d/ ) ? "$_ (default)" : "$_" } sort keys %urls ), "\n";
    print "\t-f\tforce rebuild even if certdata.txt is current\n";
    print "\t-i\tprint version info about used modules\n";
    print "\t-k\tallow URLs other than HTTPS, enable HTTP fallback (insecure)\n";
    print "\t-l\tprint license info about certdata.txt\n";
    print "\t-m\tinclude meta data in output\n";
    print "\t-n\tno download of certdata.txt (to use existing)\n";
    print wrap("\t","\t\t", "-p\tlist of Mozilla trust purposes and levels for certificates to include in output. Takes the form of a comma separated list of purposes, a colon, and a comma separated list of levels. (default: $default_mozilla_trust_purposes:$default_mozilla_trust_levels)"), "\n";
    print "\t\t  Valid purposes are:\n";
    print wrap("\t\t    ","\t\t    ", join( ", ", "ALL", @valid_mozilla_trust_purposes ) ), "\n";
    print "\t\t  Valid levels are:\n";
    print wrap("\t\t    ","\t\t    ", join( ", ", "ALL", @valid_mozilla_trust_levels ) ), "\n";
    print "\t-q\tbe really quiet (no progress output at all)\n";
    print wrap("\t","\t\t", "-s\tcomma separated list of certificate signatures/hashes to output in plain text mode. (default: $default_signature_algorithms)\n");
    print "\t\t  Valid signature algorithms are:\n";
    print wrap("\t\t    ","\t\t    ", join( ", ", "ALL", @valid_signature_algorithms ) ), "\n";
    print "\t-t\tinclude plain text listing of certificates\n";
    print "\t-u\tunlink (remove) certdata.txt after processing\n";
    print "\t-v\tbe verbose and print out processed CAs\n";
    print "\t-w <l>\twrap base64 output lines after <l> chars (default: ${opt_w})\n";
    exit;
}

sub VERSION_MESSAGE() {
    print "${0} version ${version} running Perl ${]} on ${^O}\n";
}

warning_message() unless ($opt_q || $url =~ m/^(ht|f)tps:/i );
HELP_MESSAGE() if($opt_h);

sub report($@) {
    my $output = shift;

    print STDERR $output . "\n" unless $opt_q;
}

sub is_in_list($@) {
    my $target = shift;

    return defined(List::Util::first { $target eq $_ } @_);
}

# Parses $param_string as a case insensitive comma separated list with optional
# whitespace validates that only allowed parameters are supplied
sub parse_csv_param($$@) {
    my $description = shift;
    my $param_string = shift;
    my @valid_values = @_;

    my @values = map {
        s/^\s+//;  # strip leading spaces
        s/\s+$//;  # strip trailing spaces
        uc $_      # return the modified string as upper case
    } split( ',', $param_string );

    # Find all values which are not in the list of valid values or "ALL"
    my @invalid = grep { !is_in_list($_,"ALL",@valid_values) } @values;

    if(scalar(@invalid) > 0) {
        # Tell the user which parameters were invalid and print the standard help
        # message which will exit
        print "Error: Invalid ", $description, scalar(@invalid) == 1 ? ": " : "s: ", join( ", ", map { "\"$_\"" } @invalid ), "\n";
        HELP_MESSAGE();
    }

    @values = @valid_values if(is_in_list("ALL",@values));

    return @values;
}

sub sha256 {
    my $result;
    if($Digest::SHA::VERSION || $Digest::SHA::PurePerl::VERSION) {
        open(FILE, $_[0]) or die "Can't open '$_[0]': $!";
        binmode(FILE);
        $result = $MOD_SHA->new(256)->addfile(*FILE)->hexdigest;
        close(FILE);
    } else {
        # Use OpenSSL command if Perl Digest::SHA modules not available
        $result = `"$openssl" dgst -r -sha256 "$_[0]"`;
        $result =~ s/^([0-9a-f]{64}) .+/$1/is;
    }
    return $result;
}


sub oldhash {
    my $hash = "";
    open(C, "<$_[0]") || return 0;
    while(<C>) {
        chomp;
        if($_ =~ /^\#\# SHA256: (.*)/) {
            $hash = $1;
            last;
        }
    }
    close(C);
    return $hash;
}

if( $opt_p !~ m/:/ ) {
    print "Error: Mozilla trust identifier list must include both purposes and levels\n";
    HELP_MESSAGE();
}

(my $included_mozilla_trust_purposes_string, my $included_mozilla_trust_levels_string) = split( ':', $opt_p );
my @included_mozilla_trust_purposes = parse_csv_param( "trust purpose", $included_mozilla_trust_purposes_string, @valid_mozilla_trust_purposes );
my @included_mozilla_trust_levels = parse_csv_param( "trust level", $included_mozilla_trust_levels_string, @valid_mozilla_trust_levels );

my @included_signature_algorithms = parse_csv_param( "signature algorithm", $opt_s, @valid_signature_algorithms );

sub should_output_cert(%) {
    my %trust_purposes_by_level = @_;

    foreach my $level (@included_mozilla_trust_levels) {
        # for each level we want to output, see if any of our desired purposes are
        # included
        return 1 if( defined( List::Util::first { is_in_list( $_, @included_mozilla_trust_purposes ) } @{$trust_purposes_by_level{$level}} ) );
    }

    return 0;
}

my $crt = $ARGV[0] || 'ca-bundle.crt';
(my $txt = $url) =~ s@(.*/|\?.*)@@g;

my $stdout = $crt eq '-';
my $resp;
my $fetched;

my $oldhash = oldhash($crt);

report "SHA256 of old file: $oldhash";

if(!$opt_n) {
    report "Downloading $txt ...";

    # If we have an HTTPS URL then use curl
    if($url =~ /^https:\/\//i) {
        my $curl = `curl -V`;
        if($curl) {
            if($curl =~ /^Protocols:.* https( |$)/m) {
                report "Get certdata with curl!";
                my $proto = !$opt_k ? "--proto =https" : "";
                my $quiet = $opt_q ? "-s" : "";
                my @out = `curl -Lw %{response_code} $proto $quiet -o "$txt" "$url"`;
                if(!$? && @out && $out[0] == 200) {
                    $fetched = 1;
                    report "Downloaded $txt";
                }
                else {
                    report "Failed downloading via HTTPS with curl";
                    if(-e $txt && !unlink($txt)) {
                        report "Failed to remove '$txt': $!";
                    }
                }
            }
            else {
                report "curl lacks https support";
            }
        }
        else {
            report "curl not found";
        }
    }

    # If nothing was fetched then use LWP
    if(!$fetched) {
        if($url =~ /^https:\/\//i) {
            report "Falling back to HTTP";
            $url =~ s/^https:\/\//http:\/\//i;
        }
        if(!$opt_k) {
            report "URLs other than HTTPS are disabled by default, to enable use -k";
            exit 1;
        }
        report "Get certdata with LWP!";
        if(!defined(${LWP::UserAgent::VERSION})) {
            report "LWP is not available (LWP::UserAgent not found)";
            exit 1;
        }
        my $ua  = new LWP::UserAgent(agent => "$0/$version");
        $ua->env_proxy();
        $resp = $ua->mirror($url, $txt);
        if($resp && $resp->code eq '304') {
            report "Not modified";
            exit 0 if -e $crt && !$opt_f;
        }
        else {
            $fetched = 1;
            report "Downloaded $txt";
        }
        if(!$resp || $resp->code !~ /^(?:200|304)$/) {
            report "Unable to download latest data: "
              . ($resp? $resp->code . ' - ' . $resp->message : "LWP failed");
            exit 1 if -e $crt || ! -r $txt;
        }
    }
}

my $filedate = $resp ? $resp->last_modified : (stat($txt))[9];
my $datesrc = "as of";
if(!$filedate) {
    # mxr.mozilla.org gave us a time, hg.mozilla.org does not!
    $filedate = time();
    $datesrc="downloaded on";
}

# get the hash from the download file
my $newhash= sha256($txt);

if(!$opt_f && $oldhash eq $newhash) {
    report "Downloaded file identical to previous run\'s source file. Exiting";
    if($opt_u && -e $txt && !unlink($txt)) {
        report "Failed to remove $txt: $!\n";
    }
    exit;
}

report "SHA256 of new file: $newhash";

my $currentdate = scalar gmtime($filedate);

my $format = $opt_t ? "plain text and " : "";
if($stdout) {
    open(CRT, '> -') or die "Couldn't open STDOUT: $!\n";
} else {
    open(CRT,">$crt.~") or die "Couldn't open $crt.~: $!\n";
}
print CRT <<EOT;
##
## Bundle of CA Root Certificates
##
## Certificate data from Mozilla ${datesrc}: ${currentdate} GMT
##
## Find updated versions here: https://curl.se/docs/caextract.html
##
## This is a bundle of X.509 certificates of public Certificate Authorities
## (CA). These were automatically extracted from Mozilla's root certificates
## file (certdata.txt).  This file can be found in the mozilla source tree:
## ${url}
##
## It contains the certificates in ${format}PEM format and therefore
## can be directly used with curl / libcurl / php_curl, or with
## an Apache+mod_ssl webserver for SSL client authentication.
## Just configure this file as the SSLCACertificateFile.
##
## Conversion done with mk-ca-bundle.pl version $version.
## SHA256: $newhash
##

EOT

report "Processing  '$txt' ...";
my $caname;
my $certnum = 0;
my $skipnum = 0;
my $start_of_cert = 0;
my $main_block = 0;
my $main_block_name;
my $trust_block = 0;
my $trust_block_name;
my @precert;
my $cka_value;
my $valid = 0;

open(TXT,"$txt") or die "Couldn't open $txt: $!\n";
while(<TXT>) {
    if(/\*\*\*\*\* BEGIN LICENSE BLOCK \*\*\*\*\*/) {
        print CRT;
        print if($opt_l);
        while(<TXT>) {
            print CRT;
            print if($opt_l);
            last if(/\*\*\*\*\* END LICENSE BLOCK \*\*\*\*\*/);
        }
        next;
    }
    # The input file format consists of blocks of Mozilla objects.
    # The blocks are separated by blank lines but may be related.
    elsif(/^\s*$/) {
        $main_block = 0;
        $trust_block = 0;
        next;
    }
    # Each certificate has a main block.
    elsif(/^# Certificate "(.*)"/) {
        (!$main_block && !$trust_block) or die "Unexpected certificate block";
        $main_block = 1;
        $main_block_name = $1;
        # Reset all other certificate variables.
        $trust_block = 0;
        $trust_block_name = "";
        $valid = 0;
        $start_of_cert = 0;
        $caname = "";
        $cka_value = "";
        undef @precert;
        next;
    }
    # Each certificate's main block is followed by a trust block.
    elsif(/^# Trust for (?:Certificate )?"(.*)"/) {
        (!$main_block && !$trust_block) or die "Unexpected trust block";
        $trust_block = 1;
        $trust_block_name = $1;
        if($main_block_name ne $trust_block_name) {
            die "cert name \"$main_block_name\" != trust name \"$trust_block_name\"";
        }
        next;
    }
    # Ignore other blocks.
    #
    # There is a documentation comment block, a BEGINDATA block, and a bunch of
    # blocks starting with "# Explicitly Distrust <certname>".
    #
    # The latter is for certificates that have already been removed and are not
    # included. Not all explicitly distrusted certificates are ignored at this
    # point, just those without an actual certificate.
    elsif(!$main_block && !$trust_block) {
        next;
    }
    elsif(/^#/) {
        # The commented lines in a main block are plaintext metadata that describes
        # the certificate. Issuer, Subject, Fingerprint, etc.
        if($main_block) {
            push @precert, $_ if not /^#$/;
            if(/^# Not Valid After : (.*)/) {
                my $stamp = $1;
                use Time::Piece;
                # Not Valid After : Thu Sep 30 14:01:15 2021
                my $t = Time::Piece->strptime($stamp, "%a %b %d %H:%M:%S %Y");
                my $delta = ($t->epoch - time()); # negative means no longer valid
                if($delta < 0) {
                    $skipnum++;
                    report "Skipping: $main_block_name is not valid anymore" if($opt_v);
                    $valid = 0;
                }
                else {
                    $valid = 1;
                }
            }
        }
        next;
    }
    elsif(!$valid) {
        next;
    }

    chomp;

    if($main_block) {
        if(/^CKA_CLASS CK_OBJECT_CLASS CKO_CERTIFICATE/) {
            !$start_of_cert or die "Duplicate CKO_CERTIFICATE object";
            $start_of_cert = 1;
            next;
        }
        elsif(!$start_of_cert) {
            next;
        }
        elsif(/^CKA_LABEL UTF8 \"(.*)\"/) {
            ($caname eq "") or die "Duplicate CKA_LABEL attribute";
            $caname = $1;
            if($caname ne $main_block_name) {
                die "caname \"$caname\" != cert name \"$main_block_name\"";
            }
            next;
        }
        elsif(/^CKA_VALUE MULTILINE_OCTAL/) {
            ($cka_value eq "") or die "Duplicate CKA_VALUE attribute";
            while(<TXT>) {
                last if(/^END/);
                chomp;
                my @octets = split(/\\/);
                shift @octets;
                for(@octets) {
                    $cka_value .= chr(oct);
                }
            }
            next;
        }
        else {
            next;
        }
    }

    if(!$trust_block || !$start_of_cert || $caname eq "" || $cka_value eq "") {
        die "Certificate extraction failed";
    }

    my %trust_purposes_by_level;

    if(/^CKA_CLASS CK_OBJECT_CLASS CKO_NSS_TRUST/) {
        # now scan the trust part to determine how we should trust this cert
        while(<TXT>) {
            if(/^\s*$/) {
                $trust_block = 0;
                last;
            }
            if(/^CKA_TRUST_([A-Z_]+)\s+CK_TRUST\s+CKT_NSS_([A-Z_]+)\s*$/) {
                if(!is_in_list($1,@valid_mozilla_trust_purposes)) {
                    report "Warning: Unrecognized trust purpose for cert: $caname. Trust purpose: $1. Trust Level: $2";
                } elsif(!is_in_list($2,@valid_mozilla_trust_levels)) {
                    report "Warning: Unrecognized trust level for cert: $caname. Trust purpose: $1. Trust Level: $2";
                } else {
                    push @{$trust_purposes_by_level{$2}}, $1;
                }
            }
        }

        # Sanity check that an explicitly distrusted certificate only has trust
        # purposes with a trust level of NOT_TRUSTED.
        #
        # Certificate objects that are explicitly distrusted are in a certificate
        # block that starts # Certificate "Explicitly Distrust(ed) <certname>",
        # where "Explicitly Distrust(ed) " was prepended to the original cert name.
        if($caname =~ /distrust/i ||
             $main_block_name =~ /distrust/i ||
             $trust_block_name =~ /distrust/i) {
            my @levels = keys %trust_purposes_by_level;
            if(scalar(@levels) != 1 || $levels[0] ne "NOT_TRUSTED") {
                die "\"$caname\" must have all trust purposes at level NOT_TRUSTED.";
            }
        }

        if(!should_output_cert(%trust_purposes_by_level)) {
            $skipnum ++;
            report "Skipping: $caname lacks acceptable trust level" if($opt_v);
        } else {
            my $encoded = MIME::Base64::encode_base64($cka_value, '');
            $encoded =~ s/(.{1,${opt_w}})/$1\n/g;
            my $pem = "-----BEGIN CERTIFICATE-----\n"
                    . $encoded
                    . "-----END CERTIFICATE-----\n";
            print CRT "\n$caname\n";
            my $maxStringLength = length(decode('UTF-8', $caname, Encode::FB_CROAK | Encode::LEAVE_SRC));
            print CRT ("=" x $maxStringLength . "\n");
            if($opt_t) {
                foreach my $key (sort keys %trust_purposes_by_level) {
                    my $string = $key . ": " . join(", ", @{$trust_purposes_by_level{$key}});
                    print CRT $string . "\n";
                }
            }
            if($opt_m) {
                print CRT for @precert;
            }
            if(!$opt_t) {
                print CRT $pem;
            } else {
                my $pipe = "";
                foreach my $hash (@included_signature_algorithms) {
                    $pipe = "|$openssl x509 -" . $hash . " -fingerprint -noout -inform PEM";
                    if(!$stdout) {
                        $pipe .= " >> $crt.~";
                        close(CRT) or die "Couldn't close $crt.~: $!";
                    }
                    open(TMP, $pipe) or die "Couldn't open openssl pipe: $!";
                    print TMP $pem;
                    close(TMP) or die "Couldn't close openssl pipe: $!";
                    if(!$stdout) {
                        open(CRT, ">>$crt.~") or die "Couldn't open $crt.~: $!";
                    }
                }
                $pipe = "|$openssl x509 -text -inform PEM";
                if(!$stdout) {
                    $pipe .= " >> $crt.~";
                    close(CRT) or die "Couldn't close $crt.~: $!";
                }
                open(TMP, $pipe) or die "Couldn't open openssl pipe: $!";
                print TMP $pem;
                close(TMP) or die "Couldn't close openssl pipe: $!";
                if(!$stdout) {
                    open(CRT, ">>$crt.~") or die "Couldn't open $crt.~: $!";
                }
            }
            report "Processed: $caname" if($opt_v);
            $certnum++;
        }
    }
}
close(TXT) or die "Couldn't close $txt: $!\n";
close(CRT) or die "Couldn't close $crt.~: $!\n";
unless($stdout) {
    if($opt_b && -e $crt) {
        my $bk = 1;
        while(-e "$crt.~${bk}~") {
            $bk++;
        }
        rename $crt, "$crt.~${bk}~" or die "Failed to create backup $crt.~$bk}~: $!\n";
    } elsif( -e $crt ) {
        unlink( $crt ) or die "Failed to remove $crt: $!\n";
    }
    rename "$crt.~", $crt or die "Failed to rename $crt.~ to $crt: $!\n";
}
if($opt_u && -e $txt && !unlink($txt)) {
    report "Failed to remove $txt: $!\n";
}
report "Done ($certnum CA certs processed, $skipnum skipped).";