Updated manual

[signduterre.git] / signduterre.py

#!/usr/bin/python
manual = """
Signature-du-Terroir
Construct a signature of the installed software state or check the integrity of the installation
using a previously made signature.

Usage: signduterre.py [options] FILE1 FILE2 ...

Options:
  -h, --help            show this help message and exit
  -s HEX, --salt=HEX    Enter salt in cleartext. If not given, a hexadecimal
                        salt will be suggested. The SUGGESTED[=N] keyword will
                        cause the selection of the suggested string. N is the
                        number of salts generated (default N=1). If N>1, all
                        will be printed and a random one will be used to
                        generate the signature (selection printed to STDERR).
  -p TEXT, --passphrase=TEXT
                        Enter passphrase in cleartext, the keyword
                        SUGGESTED[=N] will cause the suggested passphrase to
                        be used. If N>1, N passphrases will be printed to
                        STDERR and a random one will be used (selection
                        printed to STDERR). Entering the name of an existing
                        file will cause it to be read and a random passphrase
                        found in the file will be used (creating a signature),
                        or they will all be used in sequence (--check-file).
  -c FILE, --check-file=FILE
                        Check contents with the output of a previous run.
                        Except when the --quiet option is given, the previous
                        output will contain all information needed for the
                        program, but not the passphrase and the --execute
                        option.
  -i FILE, --input-file=FILE
                        Use names from input-file (one filename per line)
  -u USER, --user=USER  Execute $(cmd) as USER, default 'nobody' (root/sudo
                        only)
  -S, --Status          For each file, add a line with unvarying file status
                        information: st_mode, st_ino, st_dev, st_uid, st_gid,
                        and st_size (like the '?' prefix, default False)
  --Status-values=MODE  Status values to print for --Status, default MODE is
                        'fmidlugs' (file, mode, inode, device, links, uid,
                        gid, size)
  -t, --total-only      Only print the total hash, unsets --detailed-view
                        (default True)
  -d, --detailed-view   Print hashes of individual files, is unset by --total-
                        only (default False)
  -e, --execute         Interpret ${ENV} and $(cmd) (default False)
  -n, --no-execute      Explicitely do NOT Interpret ${ENV} and $(cmd)
  -m, --manual          Print the manual and exit
  -r, --release-notes   Print the release notes and exit
  -l, --license         Print license text and exit
  -v, --verbose         Print more information on output
  -q, --quiet           Print minimal information (hide filenames). If the
                        output is used with --check-file, the command line
                        options and arguments must be repeated.
  
FILE1 FILE2 ...
Names and paths of one or more files to be checked. Any name starting with a '$', eg, $PATH, will be
interpreted as an environmental variable or command according to the bash conventions:
'$ENV' and '${ENV}' as variables, '$(cmd;cmd...)' as system commands (bash --restricted -c 'cmd;cmd...' PID).
Where PID the current Process ID is (available as positional parameter $0). Do not forget to enclose the 
arguments in single ''-quotes! The commands are scanned for unwanted characters (eg, ') and these are removed. 
The use of '$(cmd;cmd...)' requires explicit use of the -e or --execute option.
 
If executed as root or sudo, $(cmd;cmd...) will be executed as 'sudo -H -u <user>' which defaults to
--user nobody ('--user root' is at your own risk). This will obviously not work when invoked as non-root/sudo.
--user root is necessary when you need to check privileged information, eg, 
you want to check the MBR with '$(dd if=/dev/hda bs=512 count=1 | od -X)'
However, as you might use --check-file with files you did not create yourself, it is important to
be warned if commands are to be executed.

Interpretation of $() ONLY works if the -e or --execute options are entered. signduterre.py can easily 
be adapted to automatically use the setting in the check-file. However, this is deemed insecure and 
commented out in the distribution version.

The -n or --no-execute option explicitely supress the interpretation of $(cmd) arguments.

Meta information from lstat on files is signed when the filename is preceded by a '?'. '?./signduterre.py' will 
extract (st_mode, st_ino, st_dev, st_nlinks, st_uid, st_gid, st_size) and hash a line of these data (visible with --verbose).
The --Status option will automatically add such a line in front of every file. Note that '?' is implied for directories.
both '/' and '?/' produce a hash of, eg,: 
lstat(/) = [st_mode=041775, st_ino=2, st_dev=234881026, st_uid=0, st_gid=80, st_size=1360]
Note that nlinks of a directory include every file in the directory, so this will check whether files have been added
to a directory.

Arguments enclosed in []-brackets will be hidden in the output. That is, '[/proc/self/exe]' will show up as
'[1]' in the output (or '[n]' with n the number of the hidden argument). This means the hidden arguments 
must be entered again when using the --check-file (-c) option.

Signature-du-Terroir

A very simple tool to generate a signature that can be used to test the integrity of files and "states" in 
a running installation. signduterre.py constructs a signature of the current system state and checks 
installation state with a previously made signature. The files are hashed with a passphrase to allow detection 
of compromised systems while running on the same system. The signature checking can be subverted, but the 
flexibillity of signduterre.py and the fact that the output of any command can be tested should hamper 
automated root-kit attacks.

signduterre.py writes a total SHA-256 hash to STDOUT of all the files and commands entered as arguments. It 
can also write a hash for each individual file (insecure). The output of a signature can be send to a file and 
later used to check with --check-file. Hashes are calculated with a hashed salt + passphrase sequence 
pre-pended to create unpredictable hashes. This procedure ensures that an attacker does not know whether or 
not the correct passphrase has been entered. An attacker can only know when to supply the requested hash 
values if she knows the passphrase or has copies available of all the tested files and output of commands to 
calculate the hashes on the fly.

SECURITY WARNINGS:

When run on a compromised system, signduterre.py can be subverted if the attacker keeps a copy of all the 
files and reroutes the open() and stat() functions, or simply delegating signduterre.py to a chroot jail with 
the original system. In principle, signduterre.py only checks whether the computer responds identically to 
when the sinature file was made. There is no theoretic barrier against a compromised computer perfectly 
simulating the original system when tested, but behaving adversely at other times. Except for running from 
clean boot media (USB?), I know of no theoretical sound solution to this problem.

However, this scenario assumes the use of unlimited resources and time. Inside a limited, real computer system, 
the attacker must make compromises on what can and what cannot be simulated with the available time and 
hardware. The idea behind signduterre.py is to "ask difficult questions" that increase the cost of simulating 
the original system high enough to make detection of successful attacks likely.signduterre.py simply intends 
to raise the bar high enoug. One point is to store the times needed to create the original hashes. This timing 
can later be used to see whether the new timings are reasonable. If the same hardware takes considerably 
longer to perform the same calculations, or needs a much longer delay before it starts, the tester might want 
to see where this time is spent.

Signature-du-Terroir works on the assumption that any attacker in control of a compromised system cannot
predict whether the passphrase entered is correct or not. An attacker can always intercept the in- and output 
of signduterre. When running with --check-file, this means the program can be made to print out OK 
irrespective of the tests. A safe use of signduterre.py is to start with a random number of incorrect 
passphrases and see whether they fail. 

THE CORRECT USE OF signduterre.py IS TO ENTER A RANDOM NUMBER OF INCORRECT PASSPHRASES FOR EACH TEST AND SEE 
WHETHER IT FAILS EVERY TIME!

On a compromised system, signduterre.py's detailed file testing (--detailed-view) is easily subverted. With a 
matched file hash, the attacker will know that the correct passphrase has been entered and can print out the 
stored hashes or 'ok's  for the rest of the checks. So if the attacker keeps any entry in the signature file 
uncompromised, she can intercept the output, test the password on the unchanged entry and substitute the 
requested hashes for the output if the hash of that entry matches. 

When checking for root-kits and other malware, it is safest to compare the signature files from a different, 
clean, system. But then you would not need signduterre.py anyway. If you have to work on the system itself, 
only use the -t or --total-only options to create signatures with a total hash and without individual file 
hashes. Such a signature can be used to check whether the system is unchanged. Another signature file WITH A 
DIFFERENT PASSPHRASE can then be used to identify the individual files that have changed. If a detailed 
signature file has the same passphrase, an attacker could use that other file to read the individual file 
hashes to check whether the correct passphrase was entered.

Using the --check-file option in itself is perfectly UNsafe. An attacker simply has to print out 'OK' to 
defeat the check. This attack can be foiled by making it unpredictable when signduterre.py should return
'OK'. This can be done by using a list of salts or passphrases where only one of them (or none!) is correct.
Any attacker will have to guess when to return 'OK'.

As generating and entering wrong passphrases and salts is tedious, it is to be expected that users will 
take shortcuts. To assist users, the '--salt SUGGESTED=<N>' option will generate a number N of salts. When 
checking, each of these salts is tried in turn. An attacker that is unable to simulate the uncompromised 
system will have to guess which one of the salts is the correct one, and whether or not the passphrase 
is correct. This increases the chances of detecting compromised systems.

The '--passphrase SUGGESTED=N' option will generate and print N passphrases. One of these is chosen at 
random for the signature. The number of the chosen passphrase is printed on STDERR with the passwords. 
When checking a file, the stored passphrases can be read in again, either by entering the passphrase 
file after the --passphrase option ('--passphrase <passphrase file>'), or directly from the --check-file. 
signduterre.py will print out the result for each of the passphrases. 

Note, that storing passphrases in a file and feeding it to signduterre.py is MUCH less secure than just 
typing them in. Moreover, it might completely defeat the purpose of signduterre.py. If future experiences 
cast any more doubt on the security of this option, it will be removed. 

For those who want to know more about what an "ideal attacker" can do, see:
Ken Thompson "Reflections on Trusting Trust" 
http://www.acm.org/classics/sep95/

David A Wheeler "Countering Trusting Trust through Diverse Double-Compiling"
http://www.acsa-admin.org/2005/abstracts/47.html

and the discussion of these at Bruce Schneier's 'Countering "Trusting Trust"'
http://www.schneier.com/blog/archives/2006/01/countering_trus.html

Manual

The intent of signduterre.py is to ensure that the signature cannot be subverted even if the system has been 
compromised by an attacker that has obtained root control over the computer and any existing signature files.

signduterre.py asks for a passphrase which is PRE-pended to every file before the hash is constructed (unless 
the passphrase is entered with an option). As long as the passphrase is not compromised, the hashes cannot 
be reconstructed. A randomly generated, unpadded base-64 encoded 16 Byte password (ie, ~22 characters) is 
suggested in interactive use. If '--passphrase SUGGESTED' is entered on the command line or no passphrase is
enetered when asked, the suggested value will be used. This value is printed to STDERR (the screen or 2) for 
safe keeping. Please, make sure you store the printed passphrase. For instance:
python signduterre.py -p SUGGESTED -s SUGGESTED /boot/* /sbin/* /bin/* \\
2> Signature_`date "+%Y%m%d_%H-%M-%S"`.pwd > Signature_`date "+%Y%m%d_%H-%M-%S"`.txt
will store the passphrase (and all error messages) in a file like 'Signature_20090630_11-14-03.pwd'
and the check-file in 'Signature_20090630_11-14-03.txt'. 

It is not secure to store files with the passphrase on the system you want to check. However, you could
pipe STDERR to some safe site.

Good passphrases are difficult to remember, so their plaintext form should be protected. To protect the 
passphrase against rainbow and brute force attacks, the passphrase is concatenated to a salt phrase and 
hashed before use (SHA-256). 

The salt phrase is requested when constructing a signature. In interactive use, an 8 byte hexadecimal 
(= 16 character) salt from /dev/urandom is suggested. If '--salt SUGGESTED' is entered on the command line
as the salt, the suggested value will be used. The salt is printed in plaintext to the output. The salt will 
make it more difficult to determine whether the same passphrase has been used to create different signatures.

At the bottom, a 'TOTAL HASH' line will be printed that hashes all the lines printed for the files. This 
includes the file names as printed on the hash lines. It is not inconceivable that existing signature files 
could have been compromised in ways that might be missed when checking the signature. The total hash will 
point out such changes.

Examples:
$ python signduterre.py --execute --detail --salt 436a73e3 --passphrase liauwefa3251EWC signduterre.py \\
 /sbin/* /bin/* /usr/bin/find /usr/bin/file /usr/bin/python* '${PATH}' \\
 > Signature_`date "+%Y%m%d_%H-%M-%S"`.txt

Prints a signature to the file Signature_20090625_14-31-54.txt (with your date). The signature contains the
SHA-256 hashes of the files, signduterre.py, /sbin/*, /bin/*,  /usr/bin/find, /usr/bin/file, 
/usr/bin/python*, and a hash of the PATH environment variable.

$ python signduterre.py --execute --detail --salt SUGGESTED --passphrase SUGGESTED --Status --detailed-view \\
  signduterre.py /sbin/* /bin/* /usr/bin/find /usr/bin/file /usr/bin/python* '${PATH}' \\
  2> Signature_`date "+%Y%m%d_%H-%M-%S"`.pwd > Signature_`date "+%Y%m%d_%H-%M-%S"`.txt

Prints a signature to the system Signature_20090625_14-31-54.txt (with your date) and the automatically 
generated password to Signature_20090625_14-31-54.pwd (with your date). The salt will be automatically 
determined. The signature contains the SHA-256 hashes of the file status and file contents of signduterre.py, 
/sbin/*, /bin/*,  /usr/bin/find, /usr/bin/file, /usr/bin/python* on separate lines, and a hash of the PATH 
environment variable.

> python signduterre.py --execute --passphrase liauwefa3251EWC -c Signature_20090625_14-31-54.txt

Will check the files and PATH variable from the signature file Signature_20090625_14-31-54.txt.

> python signduterre.py --passphrase liauwefa3251EWC -c Signature_20090625_14-31-54.txt
> python signduterre.py --passphrase liauwefa3251EWC -c Signature_20090625_14-31-54.txt --no-execute

Will both fail if Signature_20090625_14-31-54.txt contains a $(cmd) entry. The --no-execute
option is default and prevents the execute option (if reading the execute optionfrom the signature file
has been activated).

> python signduterre.py signduterre.py --salt SUGGESTED -passphrase SUGGESTED=20 signduterre.py \\
2> Signature_`date "+%Y%m%d_%H-%M-%S"`.pwd > Signature_`date "+%Y%m%d_%H-%M-%S"`.sdt

Will generate and print 20 passphrases and print a signature using one randomly chosen passphrase from these 
20. Everything is written to the files 'Signature_20090630_16-44-34.pwd' and 'Signature_20090630_16-44-34.sdt'. 

> python signduterre.py signduterre.py -c Signature_20090630_16-44-34.txt

Will check all 20 passphrases generated before from the Signature file and print the results.

> sudo python signduterre.py  -u root -s SUGGESTED -p SUGGESTED --Status-values='i' -v -e -t \\
'?/proc/self/root' '?/usr/bin/python' '$(dd if=/dev/hda bs=512 count=1 | od -X)' \\
>Signature_`date "+%Y%m%d_%H-%M-%S"`.sdt

Will hash the inode numbers of the effective root directory (eg, chroot) and the executable (python) 
together with the contents of the MBR (Master Boot Record) in Hex. It uses suggested salt and passphrase.
Accessing /dev/hda is only possible when root, so the command is entered with sudo and --user root.

"""
# 
license = """
Signature-du-Terroir
Construct a signature of the installed software state or check a previously made signature.

copyright 2009, R.J.J.H. van Son

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
""";
#
# Note that only release notes are put here
# See git repository for detailed change comments:
# git clone git://repo.or.cz/signduterre.git
releasenotes = """
20090716 - Release v0.3
20090713 - Added --quiet option
20090712 - moved from /dev/random to /dev/urandom
20090702 - Replaced -g with -p SUGGESTED[=N]
20090702 - Generating and testing lists of random salts
20090701 - Release v0.2
20090630 - Generating and testing random passphrases
20090630 - --execute works on $(cmd) only, nlinks in ?path and ? implied for directories
20090630 - Ported to Python 3.0

20090628 - Release v0.1b
20090628 - Added release-notes

20090626 - Release v0.1a
20090626 - Initial commit to Git
""";

import sys;
import os;
import stat;
import subprocess;
# if sys.stdout.isatty(): import readline;
import binascii;
import hashlib;
import re;
import time;
from optparse import OptionParser;
import base64;
import random;
import struct;

# Limit the characters that can be used in $(cmd) commands
not_allowed_chars = re.compile('[^\w\ \.\/\"\|\;\,\-\$\[\]\{\}\(\)\@\`\!\*]');

programname = "Signature-du-Terroir";
version = "0.3";

print("# Program: "+programname + " version " + version + "\n");

parser = OptionParser()
parser.add_option("-s", "--salt", metavar="HEX", 
                                  dest="salt", default=False,
                  help="Enter salt in cleartext. If not given, a hexadecimal salt will be suggested. The SUGGESTED[=N] keyword will cause the selection of the suggested string. N is the number of salts generated (default N=1). If N>1, all will be printed and a random one will be used to generate the signature (selection printed to STDERR).")
parser.add_option("-p", "--passphrase", metavar="TEXT",
                  dest="passphrase", default=False,
                  help="Enter passphrase in cleartext, the keyword SUGGESTED[=N] will cause the suggested passphrase to be used. If N>1, N passphrases will be printed to STDERR and a random one will be used (selection printed to STDERR). Entering the name of an existing file will cause it to be read and a random passphrase found in the file will be used (creating a signature), or they will all be used in sequence (--check-file).")
parser.add_option("-c", "--check-file",
                  dest="check", default=False, metavar="FILE", 
                  help="Check contents with the output of a previous run. Except when the --quiet option is given, the previous output will contain all information needed for the program, but not the passphrase and the --execute option.")
parser.add_option("-i", "--input-file",
                  dest="input", default=False, metavar="FILE", 
                  help="Use names from input-file (one filename per line)")
parser.add_option("-u", "--user",
                  dest="user", default="nobody", metavar="USER", 
                  help="Execute $(cmd) as USER, default 'nobody' (root/sudo only)")
parser.add_option("-S", "--Status",
                  dest="status", default=False, action="store_true", 
                  help="For each file, add a line with unvarying file status information: st_mode, st_ino, st_dev, st_uid, st_gid, and st_size (like the '?' prefix, default False)")
parser.add_option("--Status-values",
                  dest="statusvalues", default="fmidlugs", metavar="MODE", 
                  help="Status values to print for --Status, default MODE is 'fmidlugs' (file, mode, inode, device, links, uid, gid, size)")
parser.add_option("-t", "--total-only",
                  dest="total", default=False, action="store_true", 
                  help="Only print the total hash, unsets --detailed-view (default True)")
parser.add_option("-d", "--detailed-view",
                  dest="detail", default=False, action="store_true", 
                  help="Print hashes of individual files, is unset by --total-only (default False)")
parser.add_option("-e", "--execute",
                  dest="execute", default=False, action="store_true", 
                  help="Interpret ${ENV} and $(cmd) (default False)")
parser.add_option("-n", "--no-execute",
                  dest="noexecute", default=False, action="store_true", 
                  help="Explicitely do NOT Interpret ${ENV} and $(cmd)")
parser.add_option("-m", "--manual",
                  dest="manual", default=False, action="store_true", 
                  help="Print the manual and exit")
parser.add_option("-r", "--release-notes",
                  dest="releasenotes", default=False, action="store_true", 
                  help="Print the release notes and exit")
parser.add_option("-l", "--license",
                  dest="license", default=False, action="store_true", 
                  help="Print license text and exit")
parser.add_option("-v", "--verbose",
                  dest="verbose", default=False, action="store_true", 
                  help="Print more information on output")
parser.add_option("-q", "--quiet",
                  dest="quiet", default=False, action="store_true", 
                  help="Print minimal information (hide filenames). If the output is used with --check-file, the command line options and arguments must be repeated.")

(options, check_filenames) = parser.parse_args();
# Print license
if options.license:
        print (license, file=sys.stderr);
        exit(0);
# Print manual
if options.manual:
        print (manual, file=sys.stderr);
        exit(0);
# Print manual
if options.releasenotes:
        print ("Version: "+version, file=sys.stderr);
        print (releasenotes, file=sys.stderr);
        exit(0);

my_salt = options.salt;
my_passphrase = options.passphrase;
my_check = options.check;
my_status = options.status;
my_statusvalues = options.statusvalues;
my_verbose = options.verbose and not options.quiet;
my_quiet = options.quiet;
execute = options.execute;
noexecute = options.noexecute;
input_file = options.input;

# Set total-only with the correct default
total_only = True;
total_only = not options.detail;
if options.total: total_only = options.total;
if my_check: total_only = False;

my_user = options.user;
# Things might be executed as another user
user_change = '';
if os.getuid() == 0:
        user_change = 'sudo -H -u '+my_user+' ';
        if not my_quiet: print("User: "+my_user);

# Execute option
if execute:
        text_execute = "True";
else:
        text_execute = "False";

if execute and not my_quiet: print("Execute system commands: "+text_execute+"\n");

# --quiet option
if my_quiet: print("Quiet: True\n");

# --quiet option
if my_statusvalues != 'fmidlugs': print("Status-values: '"+my_statusvalues+"'\n");

# Measure time intervals
start_time = time.time();

dev_random = open("/dev/urandom", 'rb');

# Read the check file
passphrase_list = [];
salt_list = [];
check_hashes = {};
total_hash = "";
if my_check:
        highest_arg_used = 0;
        print("# Checking: "+my_check+"\n");
        arg_list = check_filenames;
        check_filenames = [];
        with open(my_check, 'r') as c:
                for line in c:
                        match = re.search("Execute system commands:\s+(True|False)", line);
                        if match != None:
                                # Uncomment the next line if you want automatic --execute from the check-file (DANGEROUS)
                                # execute = match.group(1).upper() == 'TRUE';
                                continue;
                                
                        match = re.search("Quiet:\s+(True|False)", line);
                        if match != None:
                                my_quiet = match.group(1).upper() == 'TRUE';
                                if my_quiet: my_verbose = False;
                                continue;
                                
                        match = re.search("Salt\:\s+\'([\w]*)\'", line);
                        if match != None:
                                salt_list.append(match.group(1));
                                continue;
                                
                        match = re.search("User\:\s+\'([\w]*)\'", line);
                        if match != None:
                                # Uncomment the next line if you want automatic --user from the check-file (DANGEROUS)
                                # my_user = match.group(1);
                                continue;
                                
                        match = re.search("Passphrase\:\s+\'([^\']*)\'", line);
                        if match != None:
                                passphrase_list.append(match.group(1));
                                continue;
                                
                        match = re.search("Status-values\:\s+\'([\w]*)\'", line);
                        if match != None:
                                my_statusvalues = match.group(1);
                                continue;
                                
                        match = re.search("^\s*([a-f0-9]+)\s+\*(TOTAL HASH)\s*$", line)
                        if match != None:
                                total_hash = match.group(1);
                                continue;
                                
                        match = re.search("^\s*([a-f0-9\-]+)\s+\*\[([0-9]+)\]\s*$", line)
                        if match != None:
                                filenumber = int(match.group(2));
                                if filenumber > highest_arg_used: highest_arg_used = filenumber;
                                # Watch out, arguments count from 0
                                check_filenames.append(arg_list[filenumber - 1]);
                                check_hashes['['+match.group(2)+']'] = match.group(1);
                                continue;

                        match = re.search("^\s*([a-f0-9\-]+)\s+\*(.*)\s*$", line)
                        if match != None:
                                check_filenames.append(match.group(2));
                                check_hashes[match.group(2)] = match.group(1);
                                continue;
        for i in range(highest_arg_used, len(arg_list)):
            check_filenames.append(arg_list[i]);
            check_hashes['['+str(i+1)+']'] = (64*'-');

# Read input-file
if input_file:
        with open(input_file, 'r') as i:
                for line in i:
                        # Clean up filename
                        current_filename = re.sub('[^\w\-\.\/\$\{\(\)\}\?\[\]]', '', line);
                        check_filenames.append(current_filename);
                        if my_check: check_hashes['['+str(i+1)+']'] = (64*'-');

stat_list = [];
for x in check_filenames:
        if os.path.isdir(x):
                x = '?'+x;
        if my_status and not x.startswith(('?', '$')):
                stat_list.append('?'+x);
        stat_list.append(x);
check_filenames = stat_list;

# Seed Pseudo Random Number Generator
seed = dev_random.read(16);
random.seed(seed);

# Read suggested salts from /dev/(u)random if needed
if my_salt:
        if my_salt.startswith('SUGGESTED'):
                N=1;
                match = re.search("([0-9][0-9]*)$", my_salt);
                if match != None:
                        N = int(match.group(1));
                for i in range(0,N):
                        salt = dev_random.read(8);
                        salt_list.append(str(binascii.hexlify(salt), 'ascii'));
        else:
                salt_list.append(my_salt);
elif len(salt_list) == 0:
        salt = dev_random.read(8);
        sys.stderr.write("Enter salt (suggest \'"+str(binascii.hexlify(salt), 'ascii')+"\'): ");
        new_salt = input();
        if not new_salt: new_salt = str(binascii.hexlify(salt), 'ascii');
        salt_list.append(new_salt);

for my_salt in salt_list:
        print("Salt: \'"+my_salt+"\'");

# Get passphrase
if my_passphrase and os.path.isfile(my_passphrase):
    with open(my_passphrase, 'r') as file:
        for line in file:
                match = re.search("Passphrase\:\s+\'([^\']*)\'", line);
                if match != None:
                        passphrase_list.append(match.group(1));
elif not my_passphrase and len(passphrase_list) == 0:
        suggest_passphrase = dev_random.read(16);
        sys.stderr.write("Enter passphrase (suggest \'"+str(base64.b64encode(suggest_passphrase), 'ascii').rstrip('=')+"\'): ");
        # How kan we make this unreadable on input?
        current_passphrase = input();
        if not current_passphrase:
            current_passphrase = str(base64.b64encode(suggest_passphrase), 'ascii').rstrip('=');
            print("Passphrase: \'"+current_passphrase+"\'", file=sys.stderr);
        passphrase_list.append(current_passphrase);
elif my_passphrase.startswith('SUGGESTED'):
    N = 1;
    match = re.search("([0-9][0-9]*)$", my_passphrase);
    if match != None:
        N = int(match.group(1));
    j = int(random.random()*N);
    for i in range(0, N):
            suggest_passphrase = dev_random.read(16);
            current_passphrase = str(base64.b64encode(suggest_passphrase), 'ascii').rstrip('=');
            print("Passphrase: \'"+current_passphrase+"\'", file=sys.stderr);
            passphrase_list.append(current_passphrase);
else:
    passphrase_list.append(my_passphrase);

if not my_check:
    j = int(random.random()*len(passphrase_list));
    passphrase_list = [passphrase_list[j]];
    print("# Selected passphrase:", j+1, file=sys.stderr);
    j = int(random.random()*len(salt_list));
    salt_list = [salt_list[j]];
    print("# Selected salt:", j+1, file=sys.stderr);

# Close /dev/(u)random
dev_random.close;

end_time = time.time();
print("# Preparation time:", end_time - start_time, "seconds\n");

pnum = 1;
snum = 1;
corrpnum = 0;
corrsnum = 0;
for my_passphrase in passphrase_list:
        snum = 1;
        for my_salt in salt_list:
                print("# Start signature: ", end='');
                if len(passphrase_list) > 1: print("passphrase -", pnum, end='');
                if len(salt_list) > 1: print(" salt -", snum, end='');
                print("");
                
                file_argnum = 0;
                start_time = time.time();
                # Construct the passphrase hash
                passphrase = hashlib.sha256();
                
                passphrase.update(bytes(my_salt, encoding='ascii'));
                passphrase.update(bytes(my_passphrase, encoding='ascii'));
                
                # Create prefix which is a hash of the salt+passphrase
                prefix = passphrase.hexdigest();
                
                # Create signature and write output
                if noexecute: execute = False;          # Doubly make sure that NOTHING is executed if required
                totalhash = hashlib.sha256();
                totalhash.update(bytes(prefix, encoding='ascii'));
                for org_filename in check_filenames:
                        # Create file hash object
                        filehash = hashlib.sha256();
                        filehash.update(bytes(prefix, encoding='ascii'));
                        # Remove []
                        filename = org_filename.strip('[').rstrip(']');
                        # Use system variables and commands
                        if filename.startswith('$'):
                                # Commands $(command)
                                match = re.search('^\$([\(\{]?)([^\)\}]+)[\)\}]?$', filename);
                                if match != None:
                                        if match.group(1) == '(':
                                                if not execute : 
                                                        error_message = "Executable argument \'"+filename+"\' only allowed with the --execute flag";
                                                        print (error_message, file=sys.stderr);
                                                        if not sys.stdout.isatty(): print(error_message);
                                                        exit(1);
                                                current_command = not_allowed_chars.sub(" ", match.group(2));
                                                current_command_line = user_change+"bash --restricted -c \'"+current_command+"\' "+str(os.getpid());
                                                if my_verbose:
                                                        print ("#", current_command_line);
                                                (status, b) = subprocess.getstatusoutput(current_command_line);
                                                if status != 0: 
                                                        print ('$('+current_command+')'+"\n"+b, file=sys.stderr);
                                                        exit(status);
                                        else:
                                                current_var = not_allowed_chars.sub(" ", match.group(2));
                                                if my_verbose:
                                                        print ("# echo $"+ current_var);
                                                b = os.environ[current_var];
                                filehash.update(bytes(bytes(b, encoding='utf8')));
                        # lstat() meta information
                        elif filename.startswith('?'):
                                if not os.path.exists(filename.lstrip('?')): 
                                        print(filename, "does not exist", file=sys.stderr)
                                        quit();
                                filestat = os.stat(filename.lstrip('?'));
                                if my_statusvalues == "": my_statusvalues = 'fmidlugs'
                                b = "";
                                if 'f' in my_statusvalues:
                                        b += 'stat('+filename.lstrip('?')+') = '
                                b += '[';
                                if 'm' in my_statusvalues:
                                        b += 'st_mode='+str(oct(filestat.st_mode))+', ';
                                if 'i' in my_statusvalues:
                                        b += 'st_ino='+str(filestat.st_ino)+', ';
                                if 'd' in my_statusvalues:
                                        b += 'st_dev='+str(filestat.st_dev)+', '
                                if 'l' in my_statusvalues:
                                        b += 'st_nlink='+str(filestat.st_nlink)+', '
                                if 'u' in my_statusvalues:
                                        b += 'st_uid='+str(filestat.st_uid)+', '
                                if 'g' in my_statusvalues:
                                        b += 'st_gid='+str(filestat.st_gid)+', '
                                if 's' in my_statusvalues:
                                        b += 'st_size='+str(filestat.st_size);
                                b = b.rstrip(', ') + ']';
                                print(b, file=sys.stderr);
                                filehash.update(bytes(b, encoding='utf8'));
                                if my_verbose:
                                        print ("# "+ b);
                        # Use file
                        else:
                                # open and read the file
                                if not os.path.exists(filename): 
                                        print(filename, "does not exist", file=sys.stderr)
                                        quit();
                                with open(filename, 'rb') as file:
                                        for b in file:
                                                filehash.update(b);
                                                
                        current_digest = filehash.hexdigest();
                        print_name = filename;
                        if my_quiet or org_filename.startswith('['):
                            file_argnum += 1;
                            print_name = '['+str(file_argnum)+']';
                        current_hash_line = current_digest+" *"+print_name
                        totalhash.update(bytes(current_hash_line, encoding='ascii'));
                        
                        # Be careful to use this ONLY after totalhash has been updated!
                        if total_only: 
                            current_hash_line = (len(current_digest)*'-')+" *"+print_name;
                        
                        # Write output
                        if not my_check:
                            if not (my_quiet and total_only):
                                    print(current_hash_line);
                        elif check_hashes[print_name] ==  (len(current_digest)*'-'):
                                if not my_quiet: print(check_hashes[print_name]+" *"+print_name);
                        elif current_digest != check_hashes[print_name]:
                                print("DIFFERENT: "+current_hash_line);
                        else:
                                print("ok"+" *"+print_name);
                
                # Handle total hash
                current_total_digest = totalhash.hexdigest();
                current_total_digest_line = current_total_digest+" *"+"TOTAL HASH";
                end_time = time.time();
                print("# \n# Total hash - Time to completion:", end_time - start_time, "seconds");
                if not my_check:
                        print(current_total_digest_line+"\n");
                elif current_total_digest != total_hash:
                        print("DIFFERENT: "+current_total_digest_line+"\n");
                else:
                        match_number = "";
                        if len(passphrase_list) > 1 or len(salt_list): match_number = " #"
                        if len(passphrase_list) > 1: match_number += " passphrase no: "+str(pnum);
                        if len(salt_list) > 1: match_number += " salt no: "+str(snum);
                        print("OK"+" *"+"TOTAL HASH"+match_number+"\n");
                        corrsnum = snum;
                        corrpnum = pnum;
                snum += 1;
        pnum += 1;
        
if len(passphrase_list) > 1:
        if corrpnum > 0:
                print("Passphrase entry:",corrpnum,"matched");
        else:
                print("No passphrase entry matched!");
if len(salt_list) > 1:
        if corrpnum > 0:
                if corrsnum > 0:
                        print("Salt entry:",corrsnum,"matched");
                else:
                        print("No salt entry matched!");
        else:
                print("No entry matched");