Provided by: syslog-ng-mod-slog_3.38.1-5_amd64 bug

NAME

       secure-logging - Forward integrity and confidentiality for system logs

SYNOPSIS

       $(slog --key-file  <host key file> --mac-file <MAC file> $RAWMSG)

DESCRIPTION

       Secure logging is an extension to syslog-ng providing forward integrity and
       confidentiality of system logs. It is implemented in form of a module and is configured as
       a template in the syslog-ng configuration file.

       The main objective of the secure logging module is to provide tamper evident logging, i.e.
       to adequately protect log records of an information system and to provide a sensor
       indicating attack attempts. The secure logging module achieves this by authentically
       encrypting each log record with an individual cryptographic key used only once and
       protecting the integrity of the whole log archive by a cryptographic authentication code.
       Each attempt to tamper with either an individual log record or the log archive itself will
       be immediately detected during log archive verification. Therefore, an attacker can no
       longer tamper with log records without being detected.

       In order to use the log file created by the secure logging module for analysis, the log
       file must first be decrypted and its integrity verified. This is achieved with a command
       line utility that is part of the secure logging module and is installed as part of the
       syslog-ng package. This utility can easily be integrated into the import module of
       existing analysis environments.

       The secure logging environment uses a cryptographic key for encrypting log entries. Each
       individual log entry is encrypted with its own key which is immediately discarded after
       successful encryption in order to provide forward integrity. An efficient algorithm
       generates the key for the next log entry based the key used for encrypting the previous
       log entry. The resulting chain of keys preserves forward integrity, i.e. a potential
       attacker cannot deduce the previous key from the current key.

       In order to ease log verification and analysis, a sequence number is added to each log
       entry. This sequence number is also added to the encryption key creating a one-to-one
       correspondence of the encryption key with the log entry. In order to prevent truncation
       attacks or deletion of individual log entries, a message authentication code (MAC) is
       iteratively applied to the complete log archive and stored in a separate file. It is used
       upon verification to check the integrity of the whole log archive.

       Here is an example of three short original log messages that will be sent to a destination
       with secure logging enabled:

           This is a log message
           And here comes another log message
           This is a log message with a longer text that is processed without any problems

       In order to inspect the status of the secure logging environment, one can check the
       sequence counter by querying the key file with the slogkey utility like this:

           user@host:~> slogkey --counter /etc/syslog-ng/host.key
           counter=3

       Counting starts at zero. This is why the counter is set to three after processing three
       messages.

       The output of the secure logging template for the three example messages is shown below.
       One clearly sees the sequence number that was prepended to each message. The colon
       indicates the end of the sequence number and the start of the original message. As three
       message were processed, the sequence counter of the key will be three.

           AAAAAAAAAAA=:k3/dYpLsgO2tUJKSauo6dycIBzW6OTC3pyA9TP+7AnqFgEojBzgC2rcK4OPfRtr8yg==
           AQAAAAAAAAA=:smw0ATISVgN+BYEu5d7OLBE7aQhHpK9Ro4MndmNgSVrqhcmRCBCj6DUnD6ku0Z29CKJ0N6LAJUgByX4Ev+g=
           AgAAAAAAAAA=:5UVybnKL1EAbgC4CLfd8HpgurjREf4LEN61/yWHSD2hbXjRD4QmQdtbwguT1chzdItKSQASps9QRIvR5Jd4AHzHfqxI4aRgdUBcNbAq26nwUCg5vPWygjmbtQaxZgCJYkry8slxCigmbTVs=

       The output of a successful verification run is shown below.

           0000000000000000: This is a log message
           0000000000000001: And here comes another log message
           0000000000000002: This is a log message with a longer text that is processed without any problems

       The original log messages have been successfully restored. Additionally, the sequence
       counter is also prepended to the clear text messages. This helps when in analyzing
       problems with a particular log entry. As real log files will contain thousands of entries.
       the sequence counter eases identification of erroneous entries.

       Before the secure logging module can be used as part of an existing syslog-ng
       installation, several preparatory activities need to be performed.

KEY GENERATION

       In order to bootstrap the system, an initial key k0 must be created and installed on the
       log host before secure logging environment is started for the first time.

       The newly created host key k0 has its counter set to 0 indicating that it represents the
       initial host key k0. This host key k0 must be kept secret and not be disclosed to third
       parties. It will be required to successfully decrypt and verify log archives processed by
       the secure logging environment. As each log entry will be encrypted with its own key, a
       new host key will be created after successful processing of a log entry and will replace
       the previous key. Therefore, the initial host key needs to be stored in a safe place
       before starting the secure logging environment, as it will be deleted from the log host
       after processing of the first log entry. The following steps must be done before starting
       the secure logging environment. Steps 1 and 2 are performed with the slogkey utility. See
       slogkey(1) for details on how to generate a master key and to derive a host key from it.
       Step 3 and 4 depend on the actual deployment in a target environment.

        1. Create a master key

        2. Derive an initial host key k0 from a previously created master key

        3. Store the initial host key k0 in a safe location outside of the log host

        4. Deploy the key k0 on the log host where the secure logging module will be used

CONFIGURATION

       Secure logging is configured by adding the corresponding statements to the syslog-ng.conf
       file. See syslog-ng.conf(5) for information on how to configure syslog-ng using the
       configuration file. Details can be found in the The syslog-ng Administrator Guide[1].

       Secure logging is implemented as a template and is configured accordingly. Apart from the
       actual template configuration, no other settings are required in order to activate secure
       logging. The secure logging is activated by placing the following statement in the
       configuration file

       template("$(slog --key-file <host key file> --mac-file <MAC file> $RAWMSG)\n");

       where

       slog
           The name of the secure logging template function. This name can be also be found by
           calling syslog-ng with the --module-registry arguments and checking the template-func
           property of the secure logging module in the corresponding output.

       --key-file or -k
           The host key. <host key file> is the full path of the file storing the host key on the
           log host. If this arguments is not supplied or does not point to a valid regular key
           file, syslog-ng will not start and a display a corresponding error message.

       --mac-file or -m
           The MAC file. <MAC file> is the full path of the MAC file on the log host. The file
           does not need to exist, as it will be automatically created upon the initial start. If
           the path is not correct, syslog-ng will not start and a display a corresponding error
           message.

       $RAWMSG
           $RAWMSG provides access to the original log message received at the source. This macro
           is only available if the store-raw-message flag was set for the source. Otherwise, an
           empty string will be passed to the secure logging template. If access to the original
           message is not available, e.g. if the source does not support the store-raw-message
           flag, then the $MSG macro can also be used. In this case, however, the integrity
           guarantee provided by secure logging is limited to the content that this macro
           provides and does not protect the complete original message.

       \n
           \n is the line separator. This is important, as the secure logging template expects
           log entries to be separated by a line separator. When detecting a line separator, the
           log entry is regarded as complete and is encrypted with the current host key.
           Therefore, only a single line separator is allowed.

       The secure logging template can be combined with any source or destination within the
       following limitations:

       •   Sources must be line-oriented. Secure logging uses a line separator in order to
           distinguish between individual log entries. Sources which provide data in a different
           format, e.g. in the form of raw data obtained directly from a database system, cannot
           currently be used with the secure logging template, as the separation of log entries
           is not clearly defined for this type of data.

       •   Only sources for which the store-raw-message flag is implemented and set do benefit
           from the integrity guarantee provided by the secure logging template. Secure logging
           aims at protecting the integrity of complete log messages including all associated
           meta-data, such as timestamps and host names.  syslog-ng parses the log message into
           its internal format and provide easy access to parts of a message through macros.
           While this is convenient when rewriting log messages, it is not helpful for secure
           logging.  syslog-ng provides the store-raw-message flag which provides access to a
           copy of the original log message after parsing. This is the log message processed and
           protected by the secure logging template. If the source does not support the
           store-raw-message flag, then the $MSG macro can also be used. However, in this case
           the integrity guarantee provided by secure logging is limited to the content that this
           macro provides.

       •   Log rotation of any kind cannot be used with destinations using secure logging. The
           reason is that log rotate will overwrite, i.e. delete previous log files. This
           destroys the cryptographic chain of trust of the log entries making recovery
           impossible. In order to allow for a an efficient handling of log files, the secure
           logging environment features iterative verification. Using iterative verification, a
           log file can be verified in steps. For this to work, the log file must first be
           downloaded from the log host, together with the corresponding host key and MAC file to
           a verification host. After this download the log file can be safely deleted from the
           log host. Verification is then performed on the verification host using the iterative
           mode of the slogverify utility. See slogverify(1) for details.

       The following example configuration shows the use of the secure logging template on a file
       destination.

           #############################################################################
           # Minimal syslog-ng.conf file with secure logging enabled. Encrypted log
           # entries will be logged to a single file called /var/log/messages.slog
           #

           @version: 3.38
           @include "scl.conf"

           source s_local {
               system();
               internal();
           };

           source s_network {
               network(
                   transport("udp")
                   port(514)
                   flags(store-raw-message)
               );
           };

           # Secure logging template definition
           template secure_logging {
               template("$(slog --key-file /etc/syslog-ng/host.key --mac-file /etc/syslog-ng/mac.dat $RAWMSG)\n");
           };

           # This configures a secure logging destination
           destination d_local {
                file("/var/log/messages.slog" template(secure_logging));
           };

           log {
               source(s_local);

               # This source has the raw message flag set
               source(s_network);

               # This statement activates secure logging for this destination
               destination(d_local);
           };

LOG VERIFICATION

       In order to analyze the log file created in a secure logging environment, the log files
       must be decrypted and their integrity be verified. Verification requires both the initial
       host key k0 and the corresponding MAC file and is performed with the slogverify utility.
       It is not normally performed on the log host where the secure logging environment is
       producing log data. In a typical deployment, log files would be retrieved from the log
       host and transferred to a central log collector where verification it performed. As
       verification requires the use of the initial host key k0, it should only be performed in a
       trusted environment.

   Normal mode
       In normal mode, a complete log archive is verified at once. In a typical environment, this
       would mean retrieving a log file together with is MAC file from a log host and retrieving
       the corresponding initial key k0 form a safe location and supplying them to the slogverify
       utility. A typical call sequence for verification in normal mode would look like this

       slogverify --key-file host0.key --mac-file mac.dat /var/log/messages.slog
       /var/log/verified/messages

       with

       host0.key
           The initial host key k0. Supplying the initial key k0 is enough for decrypting all log
           entries, as the key derivation algorithm is able to generate the necessary keys for
           all subsequent log entries based on the initial key k0.

       mac.dat
           The MAC file from the log host.

       /var/log/messages.slog
           The file containing the encrypted log entries as retrieved from a log host.

       /var/log/verified/messages
           The file receiving the plain text log after decryption.

       Log files may become large and not fit into system memory. Verification is therefore
       performed in chunks. Each part of the log file is transferred to an internal buffer on
       which verification is performed. After the buffer has been processed, the next chunk is
       fetched. An optional buffer argument can be supplied to the slogverify utility in order to
       change the default buffer size of 1000 log entries to a number suitable for the system on
       which the verification is performed, for example

       slogverify --key-file host.key --mac-file mac.dat /var/log/messages.slog
       /var/log/verified/messages 8000

       See slogverify(1) for details on verification in normal mode.

   Iterative mode
       Verification in normal mode may not be suitable for some application scenarios. Many log
       hosts use log rotation in order to preserve storage space. In log rotation, a threshold
       for the maximum amount of storage space and the number of generations is defined for
       different type of log files. When either storage space is exhausted or the number of
       generations is reached, the oldest log file will be overwritten by new incoming log data.
       This procedure is not possible in secure logging environment, as overwriting, i.e.
       deleting a log file would break the cryptographic chain that is established between the
       log entries. This comes as no surprise, as one of the main objectives of secure logging is
       to protect against deletion of log entries by a potential attacker.

       In order allow for a procedure similar to log rotation, the secure logging environment
       features an iterative mode. In iterative mode, log files can be split into different files
       and each of these files can be verified separately. Care must be taken when performing
       verification in iterative mode, as each of the different log files needs to be accompanied
       by a copy of the host key and the MAC files present on the system at the time of
       retrieval. A typical usage scenario for the iterative mode would look like this:

        1. Define a storage threshold for the secure logging file destination. In this example we
           assume 500MB.

        2. Let the secure logging environment produce log data that is written to the destination
           until 500MB are reached.

        3. Stop the secure logging environment and retrieve the log file, the host key and the
           MAC files from the log host.

        4. Delete the log file on the log host but leave host key and MAC file untouched.

        5. Restart the secure logging environment.

        6. Perform verification in iterative mode with the log file, the host key and the MAC
           just retrieved.

       Steps 2-6 have to repeated each time the log file reaches a size of 50 MB. Assuming that
       the log file parts will be named after the iteration, e.g. log.1, log.2, log.3, etc. and a
       similar convention is applied to the host keys and MAC files, a typical call sequence for
       the validation of a log file part in iterative mode after three iterations will look like
       this:

       slogverify --iterative --prev-key-file host.key.2 --prev-mac-file mac.dat.2 --mac-file
       mac.dat /var/log/messages.slog.3 /var/log/verified/messages.3

       with

       host.key.2
           The host key from the previous iteration. In this example, this is the second
           iteration.

       mac.dat.2
           The MAC file from the previous iteration. In the example, verification is performed
           during the third iteration, so the MAC file from the second iteration is required.

       mac.dat
           The current MAC file from the log host.

       /var/log/messages.slog.3
           The file part containing the encrypted log entries as retrieved from the log host
           during the third iteration.

       /var/log/verified/messages.3
           The file receiving the plain text log after decryption during the third iteration.

       In a real deployment, the above steps would typically be automated using a scripting
       engine.

       See slogverify(1) for details on verification in iterative mode.

FILES

       /usr/bin/slogkey

       /usr/bin/slogencrypt

       /usr/bin/slogverify

       /etc/syslog-ng.conf

SEE ALSO

       syslog-ng.conf(5)

       slogkey(1)

       slogencrypt(1)

       slogverify(1)

           Note
           For the detailed documentation of see The syslog-ng Administrator Guide[1]

           If you experience any problems or need help with syslog-ng, visit the syslog-ng
           mailing list[2].

           For news and notifications about of syslog-ng, visit the syslog-ng blogs[3].

           For specific information requests related to secure logging send a mail to the Airbus
           Secure Logging Team <secure-logging@airbus.com>.

AUTHOR

       This manual page was written by the Airbus Secure Logging Team
       <secure-logging@airbus.com>.

COPYRIGHT

NOTES

        1. The syslog-ng Administrator Guide
           https://www.balabit.com/documents/syslog-ng-ose-latest-guides/en/syslog-ng-ose-guide-admin/html/index.html

        2. syslog-ng mailing list
           https://lists.balabit.hu/mailman/listinfo/syslog-ng

        3. syslog-ng blogs
           https://syslog-ng.org/blogs/