Contributed by Yoshinobu Inoue <[email protected]>, 5 March
2000.
IPsec mechanism provides secure communication either for IP
layer and socket layer communication. This section should
explain how to use them. About IPsec implementation, please
refer section 23.5.4.
The current IPsec implementation supports both transport mode
and tunnel mode. However, tunnel mode comes with some restrictions.
http://www.kame.net/newsletter/
has more comprehensive examples.
Let's setup security association to deploy a secure channel
between HOST A (10.2.3.4) and HOST B (10.6.7.8). Here we show a little
complicated example. From HOST A to HOST B, only old AH is used.
From HOST B to HOST A, new AH and new ESP are combined.
Now we should choose algorithm to be used corresponding to
"AH"/"new AH"/"ESP"/"new ESP". Please refer to the setkey(8) man
page to know algorithm names. Our choice is MD5 for AH, new-HMAC-SHA1
for new AH, and new-DES-expIV with 8 byte IV for new ESP.
Key length highly depends on each algorithm. For example, key
length must be equal to 16 bytes for MD5, 20 for new-HMAC-SHA1,
and 8 for new-DES-expIV. Now we choose "MYSECRETMYSECRET",
"KAMEKAMEKAMEKAMEKAME", "PASSWORD", respectively.
OK, let's assign SPI (Security Parameter Index) for each protocol.
Please note that we need 3 SPIs for this secure channel since three
security headers are produced (one for from HOST A to HOST B, two for
from HOST B to HOST A). Please also note that SPI MUST be greater
than or equal to 256. We choose, 1000, 2000, and 3000, respectively.
(1)
HOST A ------> HOST B
(1)PROTO=AH
ALG=MD5(RFC1826)
KEY=MYSECRETMYSECRET
SPI=1000
(2.1)
HOST A <------ HOST B
<------
(2.2)
(2.1)
PROTO=AH
ALG=new-HMAC-SHA1(new AH)
KEY=KAMEKAMEKAMEKAMEKAME
SPI=2000
(2.2)
PROTO=ESP
ALG=new-DES-expIV(new ESP)
IV length = 8
KEY=PASSWORD
SPI=3000
Now, let's setup security association. Execute setkey(8)
on both HOST A and B:
# setkey -c
add 10.2.3.4 10.6.7.8 ah-old 1000 -m transport -A keyed-md5 "MYSECRETMYSECRET" ;
add 10.6.7.8 10.2.3.4 ah 2000 -m transport -A hmac-sha1 "KAMEKAMEKAMEKAMEKAME" ;
add 10.6.7.8 10.2.3.4 esp 3000 -m transport -E des-cbc "PASSWORD" ;
^D
Actually, IPsec communication doesn't process until security policy
entries will be defined. In this case, you must setup each host.
At A:
# setkey -c
spdadd 10.2.3.4 10.6.7.8 any -P out ipsec
ah/transport/10.2.3.4-10.6.7.8/require ;
^D
At B:
# setkey -c
spdadd 10.6.7.8 10.2.3.4 any -P out ipsec
esp/transport/10.6.7.8-10.2.3.4/require ;
spdadd 10.6.7.8 10.2.3.4 any -P out ipsec
ah/transport/10.6.7.8-10.2.3.4/require ;
^D
HOST A --------------------------------------> HOST E
10.2.3.4 10.6.7.8
| |
========== old AH keyed-md5 ==========>
<========= new AH hmac-sha1 ===========
<========= new ESP des-cbc ============
Another example using IPv6.
ESP transport mode is recommended for TCP port number 110 between
Host-A and Host-B.
============ ESP ============
| |
Host-A Host-B
fec0::10 -------------------- fec0::11
Encryption algorithm is blowfish-cbc whose key is "kamekame", and
authentication algorithm is hmac-sha1 whose key is "this is the test
key". Configuration at Host-A:
# setkey -c <<EOF
spdadd fec0::10[any] fec0::11[110] tcp -P out ipsec
esp/transport/fec0::10-fec0::11/use ;
spdadd fec0::11[110] fec0::10[any] tcp -P in ipsec
esp/transport/fec0::11-fec0::10/use ;
add fec0::10 fec0::11 esp 0x10001
-m transport
-E blowfish-cbc "kamekame"
-A hmac-sha1 "this is the test key" ;
add fec0::11 fec0::10 esp 0x10002
-m transport
-E blowfish-cbc "kamekame"
-A hmac-sha1 "this is the test key" ;
EOF
and at Host-B:
# setkey -c <<EOF
spdadd fec0::11[110] fec0::10[any] tcp -P out ipsec
esp/transport/fec0::11-fec0::10/use ;
spdadd fec0::10[any] fec0::11[110] tcp -P in ipsec
esp/transport/fec0::10-fec0::11/use ;
add fec0::10 fec0::11 esp 0x10001 -m transport
-E blowfish-cbc "kamekame"
-A hmac-sha1 "this is the test key" ;
add fec0::11 fec0::10 esp 0x10002 -m transport
-E blowfish-cbc "kamekame"
-A hmac-sha1 "this is the test key" ;
EOF
Note the direction of SP.
Tunnel mode between two security gateways
Security protocol is old AH tunnel mode, i.e. specified by
RFC1826, with keyed-md5 whose key is "this is the test" as
authentication algorithm.
======= AH =======
| |
Network-A Gateway-A Gateway-B Network-B
10.0.1.0/24 ---- 172.16.0.1 ----- 172.16.0.2 ---- 10.0.2.0/24
Configuration at Gateway-A:
# setkey -c <<EOF
spdadd 10.0.1.0/24 10.0.2.0/24 any -P out ipsec
ah/tunnel/172.16.0.1-172.16.0.2/require ;
spdadd 10.0.2.0/24 10.0.1.0/24 any -P in ipsec
ah/tunnel/172.16.0.2-172.16.0.1/require ;
add 172.16.0.1 172.16.0.2 ah-old 0x10003 -m any
-A keyed-md5 "this is the test" ;
add 172.16.0.2 172.16.0.1 ah-old 0x10004 -m any
-A keyed-md5 "this is the test" ;
EOF
If port number field is omitted such above then "[any]" is
employed. `-m' specifies the mode of SA to be used. "-m any" means
wild-card of mode of security protocol. You can use this SA for both
tunnel and transport mode.
and at Gateway-B:
# setkey -c <<EOF
spdadd 10.0.2.0/24 10.0.1.0/24 any -P out ipsec
ah/tunnel/172.16.0.2-172.16.0.1/require ;
spdadd 10.0.1.0/24 10.0.2.0/24 any -P in ipsec
ah/tunnel/172.16.0.1-172.16.0.2/require ;
add 172.16.0.1 172.16.0.2 ah-old 0x10003 -m any
-A keyed-md5 "this is the test" ;
add 172.16.0.2 172.16.0.1 ah-old 0x10004 -m any
-A keyed-md5 "this is the test" ;
EOF
Making SA bundle between two security gateways
AH transport mode and ESP tunnel mode is required between
Gateway-A and Gateway-B. In this case, ESP tunnel mode is applied first,
and AH transport mode is next.
========== AH =========
| ======= ESP ===== |
| | | |
Network-A Gateway-A Gateway-B Network-B
fec0:0:0:1::/64 --- fec0:0:0:1::1 ---- fec0:0:0:2::1 --- fec0:0:0:2::/64
Encryption algorithm is 3des-cbc, and authentication algorithm
for ESP is hmac-sha1. Authentication algorithm for AH is hmac-md5.
Configuration at Gateway-A:
# setkey -c <<EOF
spdadd fec0:0:0:1::/64 fec0:0:0:2::/64 any -P out ipsec
esp/tunnel/fec0:0:0:1::1-fec0:0:0:2::1/require
ah/transport/fec0:0:0:1::1-fec0:0:0:2::1/require ;
spdadd fec0:0:0:2::/64 fec0:0:0:1::/64 any -P in ipsec
esp/tunnel/fec0:0:0:2::1-fec0:0:0:1::1/require
ah/transport/fec0:0:0:2::1-fec0:0:0:1::1/require ;
add fec0:0:0:1::1 fec0:0:0:2::1 esp 0x10001 -m tunnel
-E 3des-cbc "kamekame12341234kame1234"
-A hmac-sha1 "this is the test key" ;
add fec0:0:0:1::1 fec0:0:0:2::1 ah 0x10001 -m transport
-A hmac-md5 "this is the test" ;
add fec0:0:0:2::1 fec0:0:0:1::1 esp 0x10001 -m tunnel
-E 3des-cbc "kamekame12341234kame1234"
-A hmac-sha1 "this is the test key" ;
add fec0:0:0:2::1 fec0:0:0:1::1 ah 0x10001 -m transport
-A hmac-md5 "this is the test" ;
EOF
Making SAs with the different end
ESP tunnel mode is required between Host-A and Gateway-A. Encryption
algorithm is cast128-cbc, and authentication algorithm for ESP is
hmac-sha1. ESP transport mode is recommended between Host-A and Host-B.
Encryption algorithm is rc5-cbc, and authentication algorithm for ESP is
hmac-md5.
================== ESP =================
| ======= ESP ======= |
| | | |
Host-A Gateway-A Host-B
fec0:0:0:1::1 ---- fec0:0:0:2::1 ---- fec0:0:0:2::2
Configuration at Host-A:
# setkey -c <<EOF
spdadd fec0:0:0:1::1[any] fec0:0:0:2::2[80] tcp -P out ipsec
esp/transport/fec0:0:0:1::1-fec0:0:0:2::2/use
esp/tunnel/fec0:0:0:1::1-fec0:0:0:2::1/require ;
spdadd fec0:0:0:2::1[80] fec0:0:0:1::1[any] tcp -P in ipsec
esp/transport/fec0:0:0:2::2-fec0:0:0:l::1/use
esp/tunnel/fec0:0:0:2::1-fec0:0:0:1::1/require ;
add fec0:0:0:1::1 fec0:0:0:2::2 esp 0x10001
-m transport
-E cast128-cbc "12341234"
-A hmac-sha1 "this is the test key" ;
add fec0:0:0:1::1 fec0:0:0:2::1 esp 0x10002
-E rc5-cbc "kamekame"
-A hmac-md5 "this is the test" ;
add fec0:0:0:2::2 fec0:0:0:1::1 esp 0x10003
-m transport
-E cast128-cbc "12341234"
-A hmac-sha1 "this is the test key" ;
add fec0:0:0:2::1 fec0:0:0:1::1 esp 0x10004
-E rc5-cbc "kamekame"
-A hmac-md5 "this is the test" ;
EOF
