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.TH IPSEC 7P "Sep 25, 2009"
.SH NAME
ipsec \- Internet Protocol Security Architecture
.SH DESCRIPTION
.sp
.LP
The \fBIP\fR Security Architecture (IPsec) provides protection for \fBIP\fR
datagrams. The protection can include confidentiality, strong integrity of the
data, partial sequence integrity  (replay protection), and data authentication.
\fBIPsec\fR is performed inside the \fBIP\fR processing, and it can be applied
with or without the knowledge of an Internet application.
.sp
.LP
IPsec applies to both IPv4 and IPv6. See \fBip\fR(7P) and \fBip6\fR(7P).
.SS "Protection Mechanisms"
.sp
.LP
IPsec provides two mechanisms for protecting data. The Authentication Header
(\fBAH\fR) provides strong integrity, replay protection, and data
authentication. \fBAH\fR protects as much of the \fBIP\fR datagram as it can.
\fBAH\fR cannot protect fields that change nondeterministically between sender
and receiver.
.sp
.LP
The Encapsulating Security Payload (\fBESP\fR) provides confidentiality over
what it encapsulates, as well as the services that \fBAH\fR provides, but only
over that which it encapsulates. \fBESP\fR's authentication services are
optional, which allow \fBESP\fR and \fBAH\fR to be used together on the same
datagram without redundancy.
.sp
.LP
Authentication and encryption algorithms are used for IPsec. Authentication
algorithms produce an integrity checksum value or "digest"based on the data and
a key. Encryption algorithms operate on data in units of a "block size".
.SS "NAT Traversal"
.sp
.LP
IPsec's ESP can also encapsulate itself in UDP if IKE (see \fBin.iked\fR(8))
discovers a Network Address Translator (NAT) between two communicating
endpoints.
.sp
.LP
A UDP socket can be specified as a NAT-Traversal endpoint. See \fBudp\fR(7P)
for details.
.SS "Security Associations"
.sp
.LP
\fBAH\fR and \fBESP\fR use Security Associations (\fBSA\fR). SA's are entities
that specify security properties from one host to another. Two communicating
machines require two \fBSA\fRs (at a minimum) to communicate securely. However,
communicating machines that use multicast can share the same multicast
\fBSA\fR. \fBSA\fRs are managed through the \fBpf_key\fR(7P) interface. For
IPv4, automatic \fBSA\fR management is available through the Internet Key
Exchange (IKE), as implemented by \fBin.iked\fR(8). A command-line front-end
is available by means of \fBipseckey\fR(8). An IPsec \fBSA\fR is identified by
a tuple of <\fBAH\fR or \fBESP\fR, destination \fBIP\fR address, and
\fBSPI\fR>. The Security Parameters Index (\fBSPI\fR) is an arbitrary 32-bit
value that is transmitted on the wire with an \fBAH\fR or \fBESP\fR packet. See
\fBipsecah\fR(7P) or \fBipsecesp\fR(7P)  for an explanation about where the
\fBSPI\fR falls in a protected packet.
.SS "Protection Policy and Enforcement Mechanisms"
.sp
.LP
Mechanism and policy are separate. The policy for applying IPsec is enforced on
a system-wide or per-socket level. Configuring system-wide policy and
per-tunnel policy (see Transport Mode and Tunnel Mode sections) is done via the
\fBipsecconf\fR(8) command. Configuring per-socket policy is discussed later
in this section.
.sp
.LP
System-wide IPsec policy is applied to incoming and outgoing datagrams. Some
additional rules can be applied to outgoing datagrams because of the additional
data known by the system. Inbound datagrams can be accepted or dropped. The
decision to drop or accept an inbound datagram is based on several criteria
which sometimes overlap or conflict. Conflict resolution is resolved by which
rule is parsed first, with one exception: if a policy entry states that traffic
should bypass all other policy, it is automatically be accepted. Outbound
datagrams are sent with or without protection. Protection may (or may not)
indicate specific algorithms. If policy normally would protect a datagram, it
can be bypassed either by an exception in system-wide policy or by requesting a
bypass in per-socket policy.
.sp
.LP
Intra-machine traffic policies are enforced, but actual security mechanisms are
not applied. Instead, the outbound policy on an intra-machine packet translates
into an inbound packet with those mechanisms applied.
.sp
.LP
IPsec policy is enforced in the \fBip\fR(7P) driver. Several \fBndd\fR tunables
for \fB/dev/ip\fR affect policy enforcement, including:
.sp
.ne 2
.na
\fBicmp_accept_clear_messages\fR
.ad
.RS 30n
If equal to 1 (the default), allow certain cleartext icmp messages to bypass
policy. For ICMP echo requests ("ping"messages), protect the response like the
request. If zero, treat icmp messages like other IP traffic.
.RE

.sp
.ne 2
.na
\fBigmp_accept_clear_messages\fR
.ad
.RS 30n
If 1, allow inbound cleartext IGMP messages to bypass IPsec policy.
.RE

.sp
.ne 2
.na
\fBpim_accept_clear_messages\fR
.ad
.RS 30n
If 1, allow inbound cleartext PIM messages to bypass IPsec policy.
.RE

.sp
.ne 2
.na
\fBipsec_policy_log_interval\fR
.ad
.RS 30n
IPsec logs policy failures and errors to \fB/var/log/messages\fR. To prevent
syslog from being overloaded, the IPsec kernel modules limit the rate at which
errors can be logged. You can query/set ipsec_policy_log_interval using
\fBndd\fR(8). The value is in milliseconds. Only one message can be logged per
interval.
.RE

.SS "Transport Mode and Tunnel Mode"
.sp
.LP
If IPsec is used on a tunnel, Tunnel Mode IPsec can be used to protect distinct
flows within a tunnel or to cause packets that do not match per-tunnel policy
to drop. System-wide policy is always Transport Mode.  A tunnel can use
Transport Mode IPsec or Tunnel Mode IPsec.
.SS "Per-Socket Policy"
.sp
.LP
The \fBIP_SEC_OPT\fR or \fBIPV6_SEC_OPT\fR socket option is used to set
per-socket IPsec policy.  The structure used for an \fBIP_SEC_OPT\fR request
is:
.sp
.in +2
.nf
typedef struct ipsec_req {
    uint_t      ipsr_ah_req;           /* AH request */
    uint_t      ipsr_esp_req;          /* ESP request */
    uint_t      ipsr_self_encap_req;   /* Self-Encap request */
    uint8_t     ipsr_auth_alg;         /* Auth algs for AH */
    uint8_t     ipsr_esp_alg;          /* Encr algs for ESP */
    uint8_t     ipsr_esp_auth_alg;     /* Auth algs for ESP */
} ipsec_req_t;
.fi
.in -2

.sp
.LP
The IPsec request has fields for both \fBAH\fR and \fBESP\fR. Algorithms may or
may not be specified. The actual request for \fBAH\fR or \fBESP\fR services can
take one of the following values:
.sp
.ne 2
.na
\fB\fBIPSEC_PREF_NEVER\fR\fR
.ad
.RS 23n
Bypass all policy. Only the superuser may request this service.
.RE

.sp
.ne 2
.na
\fB\fBIPSEC_PREF_REQUIRED\fR\fR
.ad
.RS 23n
Regardless of other policy, require the use of the  IPsec  service.
.RE

.sp
.LP
The following value can be logically ORed to an \fBIPSEC_PREF_REQUIRED\fR
value:
.sp
.ne 2
.na
\fB\fBIPSEC_PREF_UNIQUE\fR\fR
.ad
.RS 21n
Regardless of other policy, enforce a unique \fBSA\fR for traffic originating
from this socket.
.RE

.sp
.LP
In the event \fBIP\fR options not normally encapsulated by \fBESP\fR need to
be, the \fBipsec_self_encap_req\fR is used to add an additional \fBIP\fR header
outside the original one. Algorithm values from <\fBnet/pfkeyv2.h\fR> are as
follows:
.sp
.ne 2
.na
\fB\fBSADB_AALG_MD5HMAC\fR\fR
.ad
.RS 24n
Uses the MD5-HMAC (\fIRFC 2403\fR)  algorithm for authentication.
.RE

.sp
.ne 2
.na
\fB\fBSADB_AALG_SHA1HMAC\fR\fR
.ad
.RS 24n
Uses the SHA1-HMAC (\fIRFC 2404)\fR algorithm for authentication.
.RE

.sp
.ne 2
.na
\fB\fBSADB_EALG_DESCBC\fR\fR
.ad
.RS 24n
Uses the \fBDES\fR (\fIRFC 2405\fR) algorithm for encryption.
.RE

.sp
.ne 2
.na
\fB\fBSADB_EALG_3DESCBC\fR\fR
.ad
.RS 24n
Uses the Triple  \fBDES \fR (\fIRFC 2451\fR)   algorithm for encryption.
.RE

.sp
.ne 2
.na
\fB\fBSADB_EALG_BLOWFISH\fR\fR
.ad
.RS 24n
Uses the Blowfish (\fIRFC 2451\fR) algorithm for encryption.
.RE

.sp
.ne 2
.na
\fB\fBSADB_EALG_AES\fR\fR
.ad
.RS 24n
Uses  the  Advanced Encryption Standard  algorithm for encryption.
.RE

.sp
.ne 2
.na
\fB\fBSADB_AALG_SHA256HMAC\fR\fR
.ad
.br
.na
\fB\fBSADB_AALG_SHA384HMAC\fR\fR
.ad
.br
.na
\fB\fBSADB_AALG_SHA512HMAC\fR\fR
.ad
.RS 24n
Uses the SHA2 hash algorithms with HMAC (\fIRFC 4868\fR)for authentication.
.RE

.sp
.LP
An application should use either the \fBgetsockopt\fR(3SOCKET) or the
\fBsetsockopt\fR(3SOCKET) call to manipulate IPsec requests.  For example:
.sp
.in +2
.nf
#include <sys/socket.h>
#include <netinet/in.h>
#include <net/pfkeyv2.h>   /* For SADB_*ALG_* */
/* .... socket setup skipped */
rc = setsockopt(s, IPPROTO_IP, IP_SEC_OPT,
   (const char *)&ipsec_req, sizeof (ipsec_req_t));
.fi
.in -2

.SH SECURITY
.sp
.LP
While IPsec is an effective tool in securing network traffic, it will not make
security problems disappear. Security issues beyond the mechanisms that IPsec
offers may be discussed in similar "Security" or "Security Consideration"
sections within individual reference manual pages.
.sp
.LP
While a non-root user cannot bypass IPsec, a non-root user can set policy to be
different from the system-wide policy. For ways to prevent this, consult the
\fBndd\fR(8) variables in \fB/dev/ip\fR.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5)  for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
.TE

.SH SEE ALSO
.sp
.LP
\fBin.iked\fR(8), \fBipsecconf\fR(8), \fBipseckey\fR(8), \fBndd\fR(8),
\fBgetsockopt\fR(3SOCKET), \fBsetsockopt\fR(3SOCKET), \fBattributes\fR(5),
\fBinet\fR(7P), \fBip\fR(7P), \fBip6\fR(7P), \fBipsecah\fR(7P),
\fBipsecesp\fR(7P), \fBpf_key\fR(7P), \fBudp\fR(7P)
.sp
.LP
Kent, S., and Atkinson, R., \fIRFC 2401, Security Architecture for the Internet
Protocol\fR, The Internet Society, 1998.
.sp
.LP
Kent, S. and Atkinson, R., \fIRFC 2406, IP Encapsulating Security Payload
(ESP)\fR, The Internet Society, 1998.
.sp
.LP
Madson, C., and Doraswamy, N., \fIRFC 2405, The ESP DES-CBC Cipher Algorithm
with Explicit IV\fR, The Internet Society, 1998.
.sp
.LP
Madsen, C. and Glenn, R., \fIRFC 2403, The Use of HMAC-MD5-96 within ESP and
AH\fR, The Internet Society, 1998.
.sp
.LP
Madsen, C. and Glenn, R., \fIRFC 2404, The Use of HMAC-SHA-1-96 within ESP and
AH\fR, The Internet Society, 1998.
.sp
.LP
Pereira, R. and Adams, R., \fIRFC 2451, The ESP CBC-Mode Cipher Algorithms\fR,
The Internet Society, 1998.
.sp
.LP
Kelly, S. and Frankel, S., \fIRFC 4868, Using HMAC-SHA-256, HMAC-SHA-384, and
HMAC-SHA-512 with IPsec\fR, 2007.
.sp
.LP
Huttunen, A., Swander, B., Volpe, V., DiBurro, L., Stenberg, \fIM., RFC 3948,
UDP Encapsulation of IPsec ESP Packets\fR, The Internet Society, 2005.