ipsec(7P)
NAME
ipsec - Internet Protocol Security Architecture
DESCRIPTION
The IP Security Architecture (IPsec) provides protection for
IP datagrams. The protection can include confidentiality,
strong integrity of the data, partial sequence integrity
(replay protection), and data authentication. IPsec is per-
formed inside the IP processing, and it can be applied with
or without the knowledge of an Internet application.
IPsec applies to both IPv4 and IPv6. See ip(7P) and ip6(7P).
Protection Mechanisms
IPsec provides two mechanisms for protecting data. The
Authentication Header (AH) provides strong integrity, replay
protection, and data authentication. AH protects as much of
the IP datagram as it can. AH cannot protect fields that
change nondeterministically between sender and receiver.
The Encapsulating Security Payload (ESP) provides confiden-
tiality over what it encapsulates, as well as the services
that AH provides, but only over that which it encapsulates.
ESP's authentication services are optional, which allow ESP
and AH to be used together on the same datagram without
redundancy.
Authentication and encryption algorithms are used for IPsec.
Authentication algorithms produce an integrity checksum
value or "digest" based on the data and a key. The size of
both the digest and the key are described in authentication
algorithm pages. See authmd5h(7M) and authsha1(7M). Encryp-
tion algorithms encrypt data with a key. Encryption algo-
rithms operate on data in units of a "block size." The size
of both the block size and the key size are described in the
encryption algorithm pages. See encr3des(7M) for an example
of block size and key size descriptions.
Security Associations
AH and ESP use Security Associations (SA). SA's are entities
that specify security properties from one host to another.
Two communicating machines require two SAs (at a minimum) to
communicate securely. However, communicating machines that
use multicast can share the same multicast SA. SAs are
managed through the pf_key(7P) interface. For IPv4,
automatic SA management is available through the Internet
Key Exchange (IKE), as implemented by in.iked(1M). A
command-line front-end is available by means of
ipseckey(1M). An IPsec SA is identified by a tuple of <AH
or ESP, destination IP address, and SPI>. The Security
Parameters Index (SPI) is an arbitrary 32-bit value that is
transmitted on the wire with an AH or ESP packet. See
ipsecah(7P) or ipsecesp(7P) for an explanation about where
the SPI falls in a protected packet.
Protection Policy and Enforcement Mechanisms
Mechanism and policy are separate. The policy for applying
IPsec is enforced on a system-wide or per-socket level. Con-
figuring systemwide policy is done via the ipsecconf(1M)
command. Configuring per-socket policy is discussed later in
this section.
Systemwide 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 sys-
tem. Inbound datagrams can be accepted or dropped. The deci-
sion to drop or accept an inbound datagram is based on
several criteria which sometimes overlap or conflict. Con-
flict 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 automaticaly be
accepted. Outbound datagrams are sent with or without pro-
tection. Protection may (or may not) indicate specific algo-
rithms. If policy normally would protect a datagram, it can
be bypassed either by an exception in systemwide policy or
by requesting a bypass in per-socket policy.
Intra-machine traffic policies are enforced, but actual
security mechanisms are not applied; rather, the outbound
policy on an intra-machine packet translates into an inbound
packet with those mechanisms applied.
IPsec policy is enforced in the ip(7P) driver; several ndd
tunables for /dev/ip affect policy enforcement. These
include:
icmp_accept_clear_messages
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.
igmp_accept_clear_messages
If 1, allow inbound cleartext IGMP messages to bypass
IPsec policy.
pim_accept_clear_messages
If 1, allow inbound cleartext PIM messages to bypass
IPsec policy.
Per-Socket Policy
The IP_SEC_OPT or IPV6_SEC_OPT socket option is used to set
per-socket IPsec policy. The structure used for an
IP_SEC_OPT request is:
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;
The IPsec request has fields for both AH and ESP. Algorithms
may or may not be specified. The actual request for AH or
ESP services can take one of the following values:
IPSEC_PREF_NEVER
Bypass all policy. Only the superuser may request this
service.
IPSEC_PREF_REQUIRED
Regardless of other policy, require the use of the
IPsec service.
The following value can be logically ORed to an
IPSEC_PREF_REQUIRED value:
IPSEC_PREF_UNIQUE
Regardless of other policy, enforce a unique SA for
traffic originating from this socket.
In the event IP options not normally encapsulated by ESP
need to be, the ipsec_self_encap_req is used to add an addi-
tional IP header outside the original one. Algorithm values
from <net/pfkeyv2.h> are as follows:
SADB_AALG_MD5HMAC
Uses the MD5-HMAC (RFC 2403) algorithm for authenti-
cation. See authmd5h(7M).
SADB_AALG_SHA1HMAC
Uses the SHA1-HMAC (RFC 2404) algorithm for authenti-
cation. See authsha1(7M).
SADB_EALG_DESCBC
Uses the DES (RFC 2405) algorithm for encryption. See
encrdes(7M).
SADB_EALG_3DESCBC
Uses the Triple DES (RFC 2451)
algorithm for encryption. See encr3des(7M).
SADB_EALG_BLOWFISH
Uses the Blowfish (RFC 2451) algorithm for encryption.
See encrbfsh(7M).
SADB_EALG_AES
Uses the Advanced Encryption Standard algorithm for
encryption. See encraes(7M).
An application should use either the getsockopt(3SOCKET) or
the setsockopt(3SOCKET) call to manipulate IPsec requests.
For example:
#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));
SECURITY CONSIDERATIONS
While IPsec is an effective tool in securing network
traffic, it will not make security problems disappear. Secu-
rity issues beyond the mechanisms that IPsec offers may be
discussed in similar "Security Consideration" sections
within individual reference manual pages.
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 ndd(1M) variables in
/dev/ip.
ATTRIBUTES
See attributes(5)
for descriptions of the following attributes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Evolving |
|_____________________________|_____________________________|
SEE ALSO
in.iked(1M), ipsecconf(1M), ipseckey(1M), ndd(1M),
getsockopt(3SOCKET), setsockopt(3SOCKET), attributes(5),
authmd5h(7M), authsha1(7M), encraes(7M), encrbfsh(7M),
encrdes(7M), encr3des(7M), inet(7P), ip(7P), ip6(7P),
ipsecah(7P), ipsecesp(7P), pf_key(7P)
Kent, S., and Atkinson, R., RFC 2401, Security Architecture
for the Internet Protocol, The Internet Society, 1998.
Kent, S. and Atkinson, R., RFC 2406, IP Encapsulating Secu-
rity Payload (ESP), The Internet Society, 1998.
Madson, C., and Doraswamy, N., RFC 2405, The ESP DES-CBC
Cipher Algorithm with Explicit IV, The Internet Society,
1998.
Madsen, C. and Glenn, R., RFC 2403, The Use of HMAC-MD5-96
within ESP and AH, The Internet Society, 1998.
Madsen, C. and Glenn, R., RFC 2404, The Use of HMAC-SHA-1-96
within ESP and AH, The Internet Society, 1998.
Pereira, R. and Adams, R., RFC 2451, The ESP CBC-Mode Cipher
Algorithms, The Internet Society, 1998.
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