ipsecesp, ESP - IPsec Encapsulating Security Payload
The ipsecesp module provides confidentiality, integrity, authentica‐
tion, and partial sequence integrity (replay protection) to IP data‐
grams. The encapsulating security payload (ESP) encapsulates its data,
enabling it to protect data that follows in the datagram. For TCP pack‐
ets, ESP encapsulates the TCP header and its data only. If the packet
is an IP in IP datagram, ESP protects the inner IP datagram. Per-
socket policy allows "self-encapsulation" so ESP can encapsulate IP
options when necessary. See ipsec(7P).
Unlike the authentication header (AH), ESP allows multiple varieties of
datagram protection. (Using a single datagram protection form can
expose vulnerabilities.) For example, only ESP can be used to provide
confidentiality. But protecting confidentiality alone exposes vulnera‐
bilities in both replay attacks and cut-and-paste attacks. Similarly,
if ESP protects only integrity and does not fully protect against
eavesdropping, it may provide weaker protection than AH. See
ESP is implemented as a module that is auto-pushed on top of IP. Use
the /dev/ipsecesp entry to tune ESP with ndd(1M).
ESPuses encryption and authentication algorithms. Authentication algo‐
rithms include HMAC-MD5 and HMAC-SHA-1. Encryption algorithms include
DES, Triple-DES, Blowfish and AES. Each authentication and encryption
algorithm contain key size and key format properties. You can obtain a
list of authentication and encryption algorithms and their properties
by using the ipsecalgs(1M) command. You can also use the functions
described in the getipsecalgbyname(3NSL) man page to retrieve the prop‐
erties of algorithms. Because of export laws in the United States, not
all encryption algorithms are available outside of the United States.
ESP without authentication exposes vulnerabilities to cut-and-paste
cryptographic attacks as well as eavesdropping attacks. Like AH, ESP is
vulnerable to eavesdropping when used without confidentiality.
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ Evolving │
SEE ALSOipsecalgs(1M), ipsecconf(1M), ndd(1M), attributes(5), getipsecalgby‐
name(3NSL), ip(7P), ipsec(7P), ipsecah(7P)
Kent, S. and Atkinson, R.RFC 2406, IP Encapsulating Security Payload
(ESP), The Internet Society, 1998.
May 18, 2003 IPSECESP(7P)