From 02ed5f5ad4aab6b9734f30ca58633dc1431f46cd Mon Sep 17 00:00:00 2001 From: Michael Rash Date: Sun, 4 May 2014 09:17:27 -0400 Subject: [PATCH] [server] add --exit-parse-config option, man page updates (minor formatting change) --- client/fwknop.8.in | 10 +- doc/fwknop.man.asciidoc | 300 +++++++++++++++++++-------------------- doc/fwknopd.man.asciidoc | 208 ++++++++++++++------------- server/cmd_opts.h | 2 + server/config_init.c | 4 + server/fwknopd.8.in | 17 ++- server/fwknopd.c | 6 + server/fwknopd_common.h | 1 + server/fwknopd_errors.h | 1 + 9 files changed, 296 insertions(+), 253 deletions(-) diff --git a/client/fwknop.8.in b/client/fwknop.8.in index 250c559b..7ae4daba 100644 --- a/client/fwknop.8.in +++ b/client/fwknop.8.in @@ -2,12 +2,12 @@ .\" Title: fwknop .\" Author: [see the "AUTHORS" section] .\" Generator: DocBook XSL Stylesheets v1.78.1 -.\" Date: 01/02/2014 +.\" Date: 05/04/2014 .\" Manual: Fwknop Client .\" Source: Fwknop Client .\" Language: English .\" -.TH "FWKNOP" "8" "01/02/2014" "Fwknop Client" "Fwknop Client" +.TH "FWKNOP" "8" "05/04/2014" "Fwknop Client" "Fwknop Client" .\" ----------------------------------------------------------------- .\" * Define some portability stuff .\" ----------------------------------------------------------------- @@ -863,6 +863,12 @@ Specify the GPG home directory (\fI\-\-gpg\-home\-dir\fR)\&. Defaults to \fI~/\&.gnupg\fR\&. .RE .PP +\fBGPG_EXE\fR \fI\fR +.RS 4 +Specify the path to GPG (\fI\-\-gpg\-exe\fR)\&. Defaults to +\fI/usr/bin/gpg\fR\&. +.RE +.PP \fBSPOOF_USER\fR \fI\fR .RS 4 Set the username in the SPA data to the specified value (\fI\-U, \-\-spoof\-user\fR)\&. diff --git a/doc/fwknop.man.asciidoc b/doc/fwknop.man.asciidoc index e23478f5..a6896fb3 100644 --- a/doc/fwknop.man.asciidoc +++ b/doc/fwknop.man.asciidoc @@ -16,37 +16,37 @@ SYNOPSIS DESCRIPTION ----------- *fwknop* implements an authorization scheme known as Single Packet -Authorization (SPA) for strong service concealment. SPA requires only a single +Authorization (SPA) for strong service concealment. SPA requires only a single packet which is encrypted, non-replayable, and authenticated via an HMAC in order to communicate desired access to a service that is hidden behind a firewall in a -default-drop filtering stance. The main application of SPA is to use a +default-drop filtering stance. The main application of SPA is to use a firewall to drop all attempts to connect to services such as 'SSH' in order to make the exploitation of vulnerabilities (both 0-day and unpatched code) -more difficult. Any service that is concealed by SPA naturally cannot be -scanned for with 'Nmap'. The fwknop project supports three different +more difficult. Any service that is concealed by SPA naturally cannot be +scanned for with 'Nmap'. The fwknop project supports three different firewalls: 'iptables' on Linux systems, 'pf' on OpenBSD, and 'ipfw' on FreeBSD and Mac OS X. SPA is essentially next generation Port Knocking (PK), but solves many of the -limitations exhibited by PK while retaining its core benefits. PK limitations +limitations exhibited by PK while retaining its core benefits. PK limitations include a general difficulty in protecting against replay attacks, asymmetric ciphers and HMAC schemes are not usually possible to reliably support, and it is trivially easy to mount a DoS attack against a PK server just by spoofing an additional packet into a PK sequence as it traverses the network (thereby convincing the -PK server that the client doesn't know the proper sequence). All of these -limitation are solved by SPA. At the same time, SPA hides services behind a +PK server that the client doesn't know the proper sequence). All of these +limitation are solved by SPA. At the same time, SPA hides services behind a default-drop firewall policy, acquires SPA data passively (usually via libpcap or other means), and implements standard cryptographic operations for SPA packet authentication and encryption/decryption. This is the manual page for the *fwknop* client which is responsible for -constructing SPA packets and sending them over the network. The server side is +constructing SPA packets and sending them over the network. The server side is implemented by the *fwknopd* daemon which sniffs the network for SPA packets and interacts with the local firewall to allow SPA authenticated connections. It is recommended to read the 'fwknopd(8)' manual page as well. SPA packets generated by *fwknop* leverage HMAC for authenticated encryption -in the encrypt-then-authenticate model. Although the usage of an HMAC is +in the encrypt-then-authenticate model. Although the usage of an HMAC is currently optional (enabled via the *--use-hmac* command line switch), it is highly recommended for three reasons: '1)' without an HMAC, cryptographically strong authentication is not possible with *fwknop* unless GnuPG is used, but @@ -56,22 +56,22 @@ as the Vaudenay attack and related trickery (like the more recent "Lucky 13" attack against SSL), and '3)' the code required by the *fwknopd* daemon to verify an HMAC is much more simplistic than the code required to decrypt an SPA packet, so an SPA packet without a proper HMAC isn't even sent through the -decryption routines. Reason '3)' is why an HMAC should still be used even when +decryption routines. Reason '3)' is why an HMAC should still be used even when SPA packets are encrypted with GnuPG due to the fact that SPA data is not sent -through *libgpgme* functions unless the HMAC checks out first. GnuPG and +through *libgpgme* functions unless the HMAC checks out first. GnuPG and libgpgme are relatively complex bodies of code, and therefore limiting the ability of a potential attacker to interact with this code through an HMAC -operation helps to maintain a stronger security stance. Generating an +operation helps to maintain a stronger security stance. Generating an HMAC for SPA communications requires a dedicated key in addition to the normal encryption key, and both can be generated with the *--key-gen* option. *fwknop* encrypts SPA packets either with the 'Rijndael' block cipher or via -'GnuPG' and associated asymmetric cipher. If the symmetric encryption method +'GnuPG' and associated asymmetric cipher. If the symmetric encryption method is chosen, then as usual the encryption key is shared between the client and -server (see the *fwknopd* '@sysconfdir@/fwknop/access.conf' file for details). The actual +server (see the *fwknopd* '@sysconfdir@/fwknop/access.conf' file for details). The actual encryption key used for Rijndael encryption is generated via the standard -PBKDF1 key derivation algorithm, and CBC mode is set. If the GnuPG method -is chosen, then the encryption keys are derived from GnuPG key rings. SPA +PBKDF1 key derivation algorithm, and CBC mode is set. If the GnuPG method +is chosen, then the encryption keys are derived from GnuPG key rings. SPA packets generated by fwknop running as a client adhere to the following format (before encryption and the HMAC is applied): @@ -88,14 +88,14 @@ format (before encryption and the HMAC is applied): Each of the above fields are separated by a ":" character due to the variable length of several of the fields, and those that might contain ":" characters -are base64 encoded. The message digest (*SHA256* by default) is part of the +are base64 encoded. The message digest (*SHA256* by default) is part of the data to be encrypted and is independent of the HMAC which is appended to the -SPA packet data after encryption. The 16 digits of random data (about 53 bits) +SPA packet data after encryption. The 16 digits of random data (about 53 bits) ensures that no two SPA packets are identical, and this is in addition to and independent of using PBKDF1 for key derivation for Rijndael in CBC mode (which -uses an 8-byte random "salt" value). Because *fwknopd* tracks the SHA256 +uses an 8-byte random "salt" value). Because *fwknopd* tracks the SHA256 digest of all incoming valid SPA packets and throws out duplicates, replay -attacks are not feasible against *fwknop*. Syslog alerts are generated if a +attacks are not feasible against *fwknop*. Syslog alerts are generated if a replay is detected. By default, the *fwknop* client sends authorization packets over UDP port @@ -107,9 +107,9 @@ Also, *fwknop* can send the SPA packet over a random port via the The *fwknop* client is quite portable, and is known to run on various Linux distributions (all major distros and embedded ones such as OpenWRT as well), -FreeBSD, OpenBSD, and Cygwin on Windows. There is also a library *libfko* +FreeBSD, OpenBSD, and Cygwin on Windows. There is also a library *libfko* that both *fwknop* and *fwknopd* use for SPA packet encryption/decryption -and HMAC authentication operations. This library can be used to allow +and HMAC authentication operations. This library can be used to allow third party applications to use SPA subject to the terms of the GNU Public License (GPL). @@ -122,7 +122,7 @@ section below). *-A, --access*='':: Provide a list of ports and protocols to access on a remote computer - running *fwknopd*. The format of this list is + running *fwknopd*. The format of this list is ``+/.../+'', e.g. ``tcp/22,udp/53''. *NOTE:* The vast majority of usages for *fwknop* require the *-A* argument, but sending full commands with the *--server-cmd* argument via an SPA @@ -136,14 +136,14 @@ section below). *-R|-a|-s*:: One of these options (see below) is required to tell the remote - *fwknopd* daemon what IP should be allowed through the local firewall. It + *fwknopd* daemon what IP should be allowed through the local firewall. It is recommend to use the *-R* or *-a* options instead of *-s* in order to harden SPA communications against possible 'Man-In-The-Middle' (MITM) attacks, and on the server side set 'REQUIRE_SOURCE_ADDRESS' variable in - the '@sysconfdir@/fwknop/access.conf' file. Note that the most secure + the '@sysconfdir@/fwknop/access.conf' file. Note that the most secure option is *-a* so that *fwknop* does not have to issue an HTTP request to 'http://www.cipherdyne.org/cgi-bin/myip' in order to resolve the externally - routable IP address. Using *-a* requires that the user already knows what + routable IP address. Using *-a* requires that the user already knows what the external IP is for the network where fwknop is running. @@ -153,14 +153,14 @@ GENERAL OPTIONS Print a usage summary message and exit. *-G, --get-key*='':: - Load an encryption key/password from the specified file. The key file + Load an encryption key/password from the specified file. The key file contains a line for each destination hostname or IP address, a colon - (":"), optional space and the password, followed by a newline. Note + (":"), optional space and the password, followed by a newline. Note that the last line has to have a terminating newline character. Also note: though this is a convenience, having a file on your system with clear text passwords is not a good idea and is not recommended. Having the *fwknop* client prompt you for the key is generally more - secure. Note also that if a key is stored on disk, the *fwknop* rc + secure. Note also that if a key is stored on disk, the *fwknop* rc file is a more powerful mechanism for specifying not only the key but other options as well. @@ -175,42 +175,42 @@ GENERAL OPTIONS command line. A file descriptor set to 0 is similar to the stdin command. *--get-hmac-key*='':: - Load an HMAC key/password from the specified file. Similarly to the + Load an HMAC key/password from the specified file. Similarly to the format for the *--get-key* option, the HMAC key file contains a line for each destination hostname or IP address, a colon (":"), optional space - and the password, followed by a newline. Note that the last line has - to have a terminating newline character. Also note: though this is a + and the password, followed by a newline. Note that the last line has + to have a terminating newline character. Also note: though this is a convenience, having a file on your system with clear text passwords is - not a good idea and is not recommended. Having the *fwknop* client - prompt you for the HMAC key is generally more secure. Note also that + not a good idea and is not recommended. Having the *fwknop* client + prompt you for the HMAC key is generally more secure. Note also that if a key is stored on disk, the *fwknop* rc file is a more powerful mechanism for specifying not only the HMAC key but other options as well. *--key-gen*:: Have *fwknop* generate both Rijndael and HMAC keys that can be used for SPA - packet encryption. These keys are derived from /dev/urandom and then base64 + packet encryption. These keys are derived from /dev/urandom and then base64 encoded before being printed to stdout, and are meant to be included within - the ``$HOME/.fwknoprc'' file (or the file referenced by *--get-key*). Such + the ``$HOME/.fwknoprc'' file (or the file referenced by *--get-key*). Such keys are generally more secure than passphrases that are typed in from the command line. *--key-len*='':: - Specify the number of bytes for a generated Rijndael key. The maximum size + Specify the number of bytes for a generated Rijndael key. The maximum size is currently 128 bytes. *--hmac-key-len*='':: - Specify the number of bytes for a generated HMAC key. The maximum size is + Specify the number of bytes for a generated HMAC key. The maximum size is currently 128 bytes. *-l, --last-cmd*:: Execute *fwknop* with the command-line arguments from the previous - invocation (if any). The previous arguments are parsed out of the + invocation (if any). The previous arguments are parsed out of the '~/.fwknop.run' file. *-n, --named-config*='':: Specify the name of the configuration stanza in the ``$HOME/.fwknoprc'' - file to pull configuration and command directives. These named stanzas + file to pull configuration and command directives. These named stanzas alleviate the need for remembering the various command-line arguments for frequently used invocations of *fwknop*. See the section labeled, FWKNOPRC FILE below for a list of the valid configuration directives in @@ -219,28 +219,28 @@ GENERAL OPTIONS *--key-rijndael*='':: Specify the Rijndael key on the command line. Since the key may be visible to utilities such as 'ps' under Unix, this form should only be used where - security is not critical. Having the *fwknop* client either prompt you for + security is not critical. Having the *fwknop* client either prompt you for the key or acquire via the ``$HOME/.fwknoprc'' file is generally more secure. *--key-base64-rijndael*='':: Specify the base64 encoded Rijndael key. Since the key may be visible to utilities such as 'ps' under Unix, this form should only be used where - security is not critical. Having the *fwknop* client either prompt you for + security is not critical. Having the *fwknop* client either prompt you for the key or acquire via the ``$HOME/.fwknoprc'' file is generally more secure. *--key-base64-hmac*='':: Specify the base64 encoded HMAC key. Since the key may be visible to utilities such as 'ps' under Unix, this form should only be used where - security is not critical. Having the *fwknop* client either prompt you for + security is not critical. Having the *fwknop* client either prompt you for the key or acquire via the ``$HOME/.fwknoprc'' file is generally more secure. *--key-hmac*='':: Specify the raw HMAC key (not base64 encoded). Since the key may be visible to utilities such as 'ps' under Unix, this form should only be used where - security is not critical. Having the *fwknop* client either prompt you for + security is not critical. Having the *fwknop* client either prompt you for the key or acquire via the ``$HOME/.fwknoprc'' file is generally more secure. @@ -249,7 +249,7 @@ GENERAL OPTIONS *--save-rc-stanza*='':: Save command line arguments to the $HOME/.fwknoprc stanza specified with - the *-n* option. If the *-n* option is omitted, then the stanza name will + the *-n* option. If the *-n* option is omitted, then the stanza name will default to the destination server value (hostname or IP) given with the *-D* argument. @@ -264,7 +264,7 @@ GENERAL OPTIONS Display the last command-line arguments used by *fwknop*. *-E, --save-args-file*='':: - Save command line arguments to a specified file path. Without this + Save command line arguments to a specified file path. Without this option, and when *--no-save-args* is not also specified, then the default save args path is '~/.fwknop.run'. @@ -272,7 +272,7 @@ GENERAL OPTIONS Do not save the command line arguments given when *fwknop* is executed. *-T, --test*:: - Test mode. Generate the SPA packet data, but do not send it. Instead, + Test mode. Generate the SPA packet data, but do not send it. Instead, print a break-down of the SPA data fields, then run the data through the decryption and decoding process and print the break-down again. This is primarily a debugging feature. @@ -286,7 +286,7 @@ GENERAL OPTIONS option. *-v, --verbose*:: - Run the *fwknop* client in verbose mode. This causes *fwknop* to print + Run the *fwknop* client in verbose mode. This causes *fwknop* to print some extra information about the current command and the resulting SPA data. @@ -297,21 +297,21 @@ GENERAL OPTIONS SPA OPTIONS ----------- *--use-hmac*:: - Set HMAC mode for authenticated encryption of SPA communications. As of + Set HMAC mode for authenticated encryption of SPA communications. As of *fwknop* 2.5, this is an optional feature, but this will become the default in a future release. *-a, --allow-ip*='':: Specify IP address that should be permitted through the destination *fwknopd* server firewall (this IP is encrypted within the SPA packet - itself). This is useful to prevent a MITM attack where a SPA packet + itself). This is useful to prevent a MITM attack where a SPA packet can be intercepted en-route and sent from a different IP than the - original. Hence, if the *fwknopd* server trusts the source address + original. Hence, if the *fwknopd* server trusts the source address on the SPA packet IP header then the attacker gains access. The *-a* option puts the source address within the encrypted SPA - packet, and so thwarts this attack. The *-a* option is also + packet, and so thwarts this attack. The *-a* option is also useful to specify the IP that will be granted access when the - SPA packet itself is spoofed with the *--spoof-src* option. Another + SPA packet itself is spoofed with the *--spoof-src* option. Another related option is *-R* (see below) which instructs the *fwknop* client to automatically resolve the externally routable IP address the local system is connected to by querying a website that returns the actual @@ -329,74 +329,74 @@ SPA OPTIONS *-N, --nat-access*='':: The *fwknopd* server offers the ability to provide SPA access through an iptables firewall to an internal service by interfacing with the - iptables NAT capabilities. So, if the *fwknopd* server is protecting + iptables NAT capabilities. So, if the *fwknopd* server is protecting an internal network on an RFC-1918 address space, an external *fwknop* client can request that the server port forward an external port to an - internal IP, i.e. ``+--NAT-access 192.168.10.2,55000+''. In this case, + internal IP, i.e. ``+--NAT-access 192.168.10.2,55000+''. In this case, access will be granted to 192.168.10.2 via port 55000 to whatever service is requested via the *--access* argument (usually tcp/22). Hence, after sending such an SPA packet, one would then do ``ssh -p 55000 user@host'' and the connection would be forwarded on - through to the internal 192.168.10.2 system automatically. Note that + through to the internal 192.168.10.2 system automatically. Note that the port ``55000'' can be randomly generated via the *--nat-rand-port* argument (described later). *--nat-local*:: On the *fwknopd* server, a NAT operation can apply to the local system - instead of being forwarded through the system. That is, for iptables + instead of being forwarded through the system. That is, for iptables firewalls, a connection to, say, port 55,000 can be translated to port - 22 on the local system. By making use of the *--nat-local* argument, - the *fwknop* client can be made to request such access. This means + 22 on the local system. By making use of the *--nat-local* argument, + the *fwknop* client can be made to request such access. This means that any external attacker would only see a connection over port 55,000 instead of the expected port 22 after the SPA packet is sent. *--nat-port*:: Usually *fwknop* is used to request access to a specific port such as - tcp/22 on a system running *fwknopd*. However, by using the *--nat-port* + tcp/22 on a system running *fwknopd*. However, by using the *--nat-port* argument, it is possible to request access to a (again, such as tcp/22), but have this access granted via the specified port (so, the *-p* argument - would then be used on the 'SSH' client command line). See the + would then be used on the 'SSH' client command line). See the *--nat-local* and *--nat-access* command line arguments to *fwknop* for additional details on gaining access to services via a NAT operation. *--nat-rand-port*:: Usually *fwknop* is used to request access to a specific port such as - tcp/22 on a system running *fwknopd*. However, by using the + tcp/22 on a system running *fwknopd*. However, by using the *--nat-rand-port* argument, it is possible to request access to a particular service (again, such as tcp/22), but have this access - granted via a random translated port. That is, once the *fwknop* + granted via a random translated port. That is, once the *fwknop* client has been executed in this mode and the random port selected by *fwknop* is displayed, the destination port used by the follow-on - client must be changed to match this random port. For 'SSH', this is - accomplished via the *-p* argument. See the *--nat-local* and + client must be changed to match this random port. For 'SSH', this is + accomplished via the *-p* argument. See the *--nat-local* and *--nat-access* command line arguments to *fwknop* for additional details on gaining access to services via a NAT operation. *-p, --server-port*='':: Specify the port number where *fwknopd* accepts packets via libpcap or - ulogd pcap writer. By default *fwknopd* looks for authorization packets + ulogd pcap writer. By default *fwknopd* looks for authorization packets over UDP port 62201. *-P, --server-proto*='':: Set the protocol (udp, tcp, http, udpraw, tcpraw, or icmp) for the outgoing - SPA packet. Note: The *udpraw*, *tcpraw*, and *icmp* modes use raw sockets - and thus require root access to run. Also note: The *tcp* mode expects to + SPA packet. Note: The *udpraw*, *tcpraw*, and *icmp* modes use raw sockets + and thus require root access to run. Also note: The *tcp* mode expects to establish a TCP connection to the server before sending the SPA packet. This is not normally done, but is useful for compatibility with the Tor for - strong anonymity; see 'http://tor.eff.org/'. In this case, the + strong anonymity; see 'http://tor.eff.org/'. In this case, the *fwknopd* server will need to be configured to listen on the target TCP port (which is 62201 by default). *-Q, --spoof-src*='':: Spoof the source address from which the *fwknop* client sends SPA - packets. This requires root on the client side access since a raw - socket is required to accomplish this. Note that the *--spoof-user* + packets. This requires root on the client side access since a raw + socket is required to accomplish this. Note that the *--spoof-user* argument can be given in this mode in order to pass any *REQUIRE_USERNAME* keyword that might be specified in '@sysconfdir@/fwknop/access.conf'. *-r, --rand-port*:: Instruct the *fwknop* client to send an SPA packet over a random - destination port between 10,000 and 65535. The *fwknopd* server must + destination port between 10,000 and 65535. The *fwknopd* server must use a *PCAP_FILTER* variable that is configured to accept such packets. For example, the *PCAP_FILTER* variable could be set to: ``+udp dst portrange 10000-65535+''. @@ -406,10 +406,10 @@ SPA OPTIONS the *fwknopd* daemon/service to query a web server that returns the caller's IP address (as seen by the web server). In some cases, this is needed to determine the IP address that should be allowed through the - iptables policy at the remote fwknopd server side. This is useful if + iptables policy at the remote fwknopd server side. This is useful if the *fwknop* client is being used on a system that is behind an obscure NAT address. Presently, *fwknop* uses the URL: - 'http://www.cipherdyne.org/cgi-bin/myip' to resolve the caller IP. Note + 'http://www.cipherdyne.org/cgi-bin/myip' to resolve the caller IP. Note that it is generally more secure to use the *-a* option if the externally routable IP address for the client is already known to the user since this elminates the need for *fwknop* to issue an HTTP request. @@ -424,9 +424,9 @@ SPA OPTIONS special-case IP address ``+0.0.0.0+'' which will inform the destination *fwknopd* SPA server to use the source IP address from which the SPA packet originates as the IP that will be allowed through upon - modification of the firewall ruleset. This option is useful if the + modification of the firewall ruleset. This option is useful if the *fwknop* client is deployed on a machine that is behind a NAT device and - the external IP is not known. However, usage of this option is not + the external IP is not known. However, usage of this option is not recommended, and either the *-a* or *-R* options should be used instead. The permit-address options *-s*, *-R* and *-a* are mutually exclusive. @@ -436,7 +436,7 @@ SPA OPTIONS *-f, --fw-timeout*='':: Specify the length of time (seconds) that the remote firewall rule that - grants access to a service is to remain active. The default maintained by + grants access to a service is to remain active. The default maintained by *fwknopd* is 30 seconds, but any established connection can be kept open after the initial accept rule is deleted through the use of a connection tracking mechanism that may be offered by the firewall. @@ -444,38 +444,38 @@ SPA OPTIONS *-C, --server-cmd*='':: Instead of requesting access to a service with an SPA packet, the *--server-cmd* argument specifies a command that will be executed by - the *fwknopd* server. The command is encrypted within the SPA packet + the *fwknopd* server. The command is encrypted within the SPA packet and sniffed off the wire (as usual) by the *fwknopd* server. *-H, --http-proxy*='[:port]':: Specify an HTTP proxy that the *fwknop* client will use to send the SPA - packet through. Using this option will automatically set the SPA packet + packet through. Using this option will automatically set the SPA packet transmission mode (usually set via the *--server-proto* argument) to - "http". You can also specify the proxy port by adding ":" to + "http". You can also specify the proxy port by adding ":" to the proxy host name or ip. *-m, --digest-type*='':: - Specify the message digest algorithm to use in the SPA data. Choices + Specify the message digest algorithm to use in the SPA data. Choices are: *MD5*, *SHA1*, *SHA256* (the default), *SHA384*, and *SHA512*. *-M, --encryption-mode*='':: Specify the encryption mode when AES is used for encrypting SPA packets. The default is CBC mode, but others can be chosen such as CFB or OFB as long as this is also specified in the '@sysconfdir@/fwknop/access.conf' file on the - server side via the ENCRYPTION_MODE variable. In general, it is + server side via the ENCRYPTION_MODE variable. In general, it is recommended to not include this argument and let the default (CBC) apply. Note that the string ``legacy'' can be specified in order to generate SPA packets with the old initialization vector strategy used by versions of - *fwknop* prior to 2.5. With the 2.5 release, *fwknop* generates + *fwknop* prior to 2.5. With the 2.5 release, *fwknop* generates initialization vectors in a manner that is compatible with OpenSSL via the PBKDF1 algorithm. *--time-offset-plus*='