SETKEY(8)

💅 SETKEY(8) — System Manager's Manual

bestie, welcome to setkey(8) — the manual page for manually manipulating the IPsec SA/SP database. Yes, it’s a lot. Yes, we’re getting through all of it. 🫶

✨ NAME ✨

setkey — manually manipulate the IPsec SA/SP database

🌸 SYNOPSIS 🌸

setkey [-v] -c
setkey [-v] -f filename
setkey [-v] -e script
setkey [-Pgltv] -D
setkey [-Pv] -F
setkey [-h] -x

🦋 DESCRIPTION 🦋

Okay so the setkey utility adds, updates, dumps, or flushes Security Association Database (SAD) entries as well as Security Policy Database (SPD) entries in the kernel. Main character energy, honestly.

The setkey utility takes a series of operations from the standard input (if invoked with -c), from the file named filename (if invoked with -f filename), or from the command line argument following the option (if invoked with -e script). Pick your lane, bestie. 💅

• -D — Dump the SAD entries. If it’s with -P, the SPD entries are dumped.
• -F — Flush the SAD entries. If it’s with -P, the SPD entries are flushed.
• -g — Only SPD entries with global scope are dumped with -D and -P flags.
• -t — Only SPD entries with ifnet scope are dumped with -D and -P flags. Such SPD entries are linked to the corresponding if_ipsec(4) virtual tunneling interface.
• -h — Add hexadecimal dump on -x mode.
• -l — Loop forever with short output on -D.
• -v — Be verbose. The program will dump messages exchanged on PF_KEY socket, including messages sent from other processes to the kernel.
• -x — Loop forever and dump all the messages transmitted to PF_KEY socket. -xx makes each timestamp unformatted.

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🎀 Configuration syntax 🎀

With -c or -f on the command line, setkey accepts the following configuration syntax. Lines starting with hash signs (#) are treated as comment lines. iykyk ✨

• add [-46n] src dst protocol spi [extensions] algorithm ... ; — Add an SAD entry. add can fail with multiple reasons, including when the key length does not match the specified algorithm.
• get [-46n] src dst protocol spi ; — Show an SAD entry.
• delete [-46n] src dst protocol spi ; — Remove an SAD entry.
• deleteall [-46n] src dst protocol ; — Remove all SAD entries that match the specification.
• flush [protocol] ; — Clear all SAD entries matched by the options. -F on the command line achieves the same functionality.
• dump [protocol] ; — Dumps all SAD entries matched by the options. -D on the command line achieves the same functionality.
• spdadd [-46n] src_range dst_range upperspec policy ; — Add an SPD entry.
• spddelete [-46n] src_range dst_range upperspec -P direction ; — Delete an SPD entry.
• spdflush ; — Clear all SPD entries. -FP on the command line achieves the same functionality.
• spddump ; — Dumps all SPD entries. -DP on the command line achieves the same functionality.

Meta-arguments are as follows:

• src, dst — Source/destination of the secure communication is specified as IPv4/v6 address. The setkey utility can resolve an FQDN into numeric addresses. If the FQDN resolves into multiple addresses, setkey will install multiple SAD/SPD entries into the kernel by trying all possible combinations. -4, -6 and -n restricts the address resolution of FQDN in certain ways. -4 and -6 restrict results into IPv4/v6 addresses only, respectively. -n avoids FQDN resolution and requires addresses to be numeric addresses.
• protocol — protocol is one of following:
  • esp — ESP based on rfc2406
  • esp-old — ESP based on rfc1827
  • ah — AH based on rfc2402
  • ah-old — AH based on rfc1826
  • ipcomp — IPComp
  • tcp — TCP-MD5 based on rfc2385
• spi — Security Parameter Index (SPI) for the SAD and the SPD. spi must be a decimal number, or a hexadecimal number with 0x prefix. SPI values between 0 and 255 are reserved for future use by IANA and they cannot be used.
• extensions — take some of the following:
  • -m mode — Specify a security protocol mode for use. mode is one of following: transport, tunnel or any. The default value is any.
  • -r size — Specify the bitmap size in octets of the anti-replay window. size is a 32-bit unsigned integer, and its value is one eighth of the anti-replay window size in packets. If size is zero or not specified, an anti-replay check does not take place.
  • -u id — Specify the identifier of the policy entry in SPD. See policy.
  • -f pad_option — defines the content of the ESP padding. pad_option is one of following:
    • zero-pad — All of the padding are zero.
    • random-pad — A series of randomized values are set.
    • seq-pad — A series of sequential increasing numbers started from 1 are set.
  • -f nocyclic-seq — Do not allow cyclic sequence number.
  • -lh time, -ls time — Specify hard/soft life time duration of the SA.
  • -natt oai [ sport ] oar [ dport ] — Manually configure NAT-T for the SA, by specifying initiator oai and requestor oar ip addresses and ports. Note that the [ and ] symbols are part of the syntax for the ports specification, not indication of the optional components.
  • -natt_mtu fragsize — Configure NAT-T fragment size.
  • -esn — Enable Extended Sequence Number extension for this SA.
  • -hwif ifname — Request hardware offload to the specified interface ifname (only). By default offload occurs to all capable interfaces.
• algorithm — these forms are giving:
  • -E ealgo key — Specify an encryption or Authenticated Encryption with Associated Data (AEAD) algorithm ealgo for ESP.
  • -E ealgo key -A aalgo key — Specify a encryption algorithm ealgo, as well as a payload authentication algorithm aalgo, for ESP.
  • -A aalgo key — Specify an authentication algorithm for AH.
  • -C calgo [-R] — Specify a compression algorithm for IPComp. If -R is specified, the spi field value will be used as the IPComp CPI (compression parameter index) on wire as is. If -R is not specified, the kernel will use well-known CPI on wire, and spi field will be used only as an index for kernel internal usage.

key must be double-quoted character string, or a series of hexadecimal digits preceded by 0x.

Possible values for ealgo, aalgo and calgo are specified in separate section.

• src_range, dst_range — These are selections of the secure communication specified as IPv4/v6 address or IPv4/v6 address range, and it may accompany TCP/UDP port specification. This takes the following form:

address
address/prefixlen
address[port]
address/prefixlen[port]

prefixlen and port must be a decimal number. The square brackets around port are necessary and are not manpage metacharacters. For FQDN resolution, the rules applicable to src and dst apply here as well.

• upperspec — The upper layer protocol to be used. You can use one of the words in /etc/protocols as upperspec, as well as icmp6, ip4, or any. The word any stands for “any protocol”. The protocol number may also be used to specify the upperspec. A type and code related to ICMPv6 may also be specified as an upperspec. The type is specified first, followed by a comma and then the relevant code. The specification must be placed after icmp6. The kernel considers a zero to be a wildcard but cannot distinguish between a wildcard and an ICMPv6 type which is zero. The following example shows a policy where IPSec is not required for inbound Neighbor Solicitations:

spdadd ::/0 ::/0 icmp6 135,0 -P in none;

NOTE: upperspec does not work in the forwarding case at this moment, as it requires extra reassembly at forwarding node, which is not implemented at this moment. Although there are many protocols in /etc/protocols, protocols other than TCP, UDP and ICMP may not be suitable to use with IPsec.

• policy — policy is expressed in one of the following three formats:

-P direction discard
-P direction none
-P direction ipsec protocol/mode/src-dst/level [...]

• direction — The direction of a policy must be specified as one of: out or in.
• policy level — The direction is followed by one of the following policy levels: discard, none, or ipsec.
  • The discard policy level means that packets matching the supplied indices will be discarded.
  • The none policy level means that IPsec operations will not take place on the packet.
  • The ipsec policy level means that IPsec operation will take place onto the packet.
• protocol/mode/src-dst/level — The protocol/mode/src-dst/level statement gives the rule for how to process the packet.
  • The protocol is specified as ah, esp or ipcomp.
  • The mode is either transport or tunnel.

If mode is tunnel, you must specify the end-point addresses of the SA as src and dst with a dash, -, between the addresses.

If mode is transport, both src and dst can be omitted.

The level is one of the following: default, use, require or unique. If the SA is not available in every level, the kernel will request the SA from the key exchange daemon. 🫶

• default — the kernel just uses the system-wide default protocol when it processes the packet, like the one from the esp_trans_deflev sysctl variable. lowkey "whatever the house default is" energy 💅
• use — the kernel will use an SA if one's available, and if not it just passes the packet along as it normally would. so chill, so unbothered ✨
• require — an SA is required whenever the kernel sends a packet matching that policy. no SA, no vibes, no packet. periodt 💀
• unique — same as require, but it also lets the policy bind with the unique out-bound SA. it's giving main character energy 👑

fr fr, like — if you set the policy level to unique, racoon(8) (ports/security/ipsec-tools) will configure the SA for that policy. and if you're out here configuring the SA by manual keying for that policy, you can drop the decimal number as the policy identifier after unique, separated by colon : — as in unique:number. for the bind to actually work, number has to be between 1 and 32767, which corresponds to extensions -u of manual SA configuration 🌸

When you want to use an SA bundle, bestie, you can define multiple rules. so if an IP header was followed by an AH header followed by an ESP header followed by an upper layer protocol header, the rule would be:

esp/transport//require ah/transport//require;

The rule order is very important. like, do not play with it 🙈

Note that “discard” and “none” are not in the syntax described in ipsec_set_policy(3). there are small but important differences in the syntax — see ipsec_set_policy(3) for details. iykyk 🧚

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✨ ALGORITHMS ✨

here's the whole roster of supported algorithms. slay 🎀

Authentication Algorithms

these can be used as aalgo in the -A aalgo of the protocol parameter:

• hmac-sha1
  • 160 — ah/esp: rfc2404
  • 160 — ah-old/esp-old: 128bit ICV (no document)
• null
  • 0 to 2048 — for debugging
• hmac-sha2-256
  • 256 — ah/esp: 128bit ICV (RFC4868)
  • 256 — ah-old/esp-old: 128bit ICV (no document)
• hmac-sha2-384
  • 384 — ah/esp: 192bit ICV (RFC4868)
  • 384 — ah-old/esp-old: 128bit ICV (no document)
• hmac-sha2-512
  • 512 — ah/esp: 256bit ICV (RFC4868)
  • 512 — ah-old/esp-old: 128bit ICV (no document)
• aes-xcbc-mac
  • 128 — ah/esp: 96bit ICV (RFC3566)
  • 128 — ah-old/esp-old: 128bit ICV (no document)
• tcp-md5
  • 8 to 640 — tcp: rfc2385
• chacha20-poly1305
  • 256 — ah/esp: 128bit ICV (RFC7634)

Encryption Algorithms

these can be used as the ealgo in the -E ealgo of the protocol parameter:

• null
  • 0 to 2048 — rfc2410
• aes-cbc
  • 128/192/256 — rfc3602
• aes-ctr
  • 160/224/288 — rfc3686
• aes-gcm-16
  • 160/224/288 — AEAD; rfc4106
• chacha20-poly1305
  • 256 — rfc7634

heads up bestie: the first 128/192/256 bits of a key for aes-ctr or aes-gcm-16 get used as the AES key, and the remaining 32 bits get used as the nonce. don't @ me, that's just how it is 💅

AEAD encryption algorithms like aes-gcm-16 already include authentication, so do not pair them with a separate authentication algorithm via -A. that's a whole mess you do not need 😭

Compression Algorithms

these can be used as the calgo in the -C calgo of the protocol parameter:

• deflate — rfc2394

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🌈 EXIT STATUS 🌈

The setkey utility exits 0 on success, and >0 if an error occurs. simple as that, icon behaviour ✨

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💖 EXAMPLES 💖

Add an ESP SA between two IPv6 addresses using the AES-GCM AEAD algorithm.

add 3ffe:501:4819::1 3ffe:501:481d::1 esp 123457
        -E aes-gcm-16 0x3ffe050148193ffe050148193ffe050148193ffe ;

Add an authentication SA between two FQDN specified hosts:

add -6 myhost.example.com yourhost.example.com ah 123456
        -A hmac-sha2-256 "AH SA configuration!" ;

Get the SA information associated with first example above:

get 3ffe:501:4819::1 3ffe:501:481d::1 ah 123456 ;

Flush all entries from the database:

flush ;

Dump the ESP entries from the database:

dump esp ;

Add a security policy between two networks that uses ESP in tunnel mode:

spdadd 10.0.11.41/32[21] 10.0.11.33/32[any] any
        -P out ipsec esp/tunnel/192.168.0.1-192.168.1.2/require ;

Use TCP MD5 between two numerically specified hosts:

add 10.1.10.34 10.1.10.36 tcp 0x1000 -A tcp-md5 "TCP-MD5 BGP secret" ;
add 10.1.10.36 10.1.10.34 tcp 0x1001 -A tcp-md5 "TCP-MD5 BGP secret" ;

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🦋 SEE ALSO 🦋

• ipsec_set_policy(3)
• if_ipsec(4)
• racoon(8) (ports/security/ipsec-tools)
• sysctl(8)

also, changed manual key configuration for IPsec, https://www.kame.net/newsletter/19991007/, October 1999 — vintage but valid 🎀

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👑 HISTORY 👑

The setkey utility first appeared in WIDE Hydrangea IPv6 protocol stack kit. the utility was completely re-designed in June 1998, and it first appeared in FreeBSD 4.0. glow-up of the century tbh ⭐

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💀 BUGS 💀

The setkey utility should report and handle syntax errors better. literally could be doing more 🙈

For IPsec gateway configuration, src_range and dst_range with TCP/UDP port number do not work, as the gateway does not reassemble packets (cannot inspect upper-layer headers). so that's a thing, no cap 😭

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aight that's the whole vibe check, bestie — page courtesy of Debian, dated August 25, 2024, and it's SETKEY(8) signing off 🫶💜