1. ipsec-tools on ubuntu14.04

管梓

2023-12-01

1.When configuring the kernel, it is important, to turn on the following features:

Networking support (NET) [Y/n/?] y
*
* Networking options
*
PF_KEY sockets (NET_KEY) [Y/n/m/?] y
IP: AH transformation (INET_AH) [Y/n/m/?] y
IP: ESP transformation (INET_ESP) [Y/n/m/?] y
IP: IPsec user configuration interface (XFRM_USER) [Y/n/m/?] y

Cryptographic API (CRYPTO) [Y/n/?] y
HMAC support (CRYPTO_HMAC) [Y/n/?] y
Null algorithms (CRYPTO_NULL) [Y/n/m/?] y
MD5 digest algorithm (CRYPTO_MD5) [Y/n/m/?] y
SHA1 digest algorithm (CRYPTO_SHA1) [Y/n/m/?] y
DES and Triple DES EDE cipher algorithms (CRYPTO_DES) [Y/n/m/?] y
AES cipher algorithms (CRYPTO_AES) [Y/n/m/?] y

2. apt-get install racoon ipsec-tools

3. Manual keyed connections using setkey

A manual keyed connection means that all parameters needed for the setup of the connection are provided by the administrator. The IKE protocol is not used to automatically authenticate the peers and negotiate these parameters. The administrator decides which protocol, algorithm and key to use for the creation of the security associations and populates the security association database (SAD) accordingly.

Transport Mode

This section will first cover the setup of a manual keyed connection in transport mode. This is probably the best way to start because it is the simplest connection to setup. This section assumes that two machines with the IP addresses 192.168.1.100 and 192.168.2.100 communicate using IPsec.

All parameters stored in the SAD and the SPD can be modified using the setkey command. This command has a quite exhaustive man page. Therefore only the options needed for the setup of a connection in transport mode are covered here. setkey reads its commands from a file when invoked with setkey -f /etc/setkey.conf. A suitable /etc/setkey.conf file is shown in following listing.

#!/usr/sbin/setkey -f

# Configuration for 192.168.1.100

# Flush the SAD and SPD
flush;
spdflush;

# Attention: Use this keys only for testing purposes!
# Generate your own keys!

# AH SAs using 128 bit long keys
add 192.168.1.100 192.168.2.100 ah 0x200 -A hmac-md5
0xc0291ff014dccdd03874d9e8e4cdf3e6;
add 192.168.2.100 192.168.1.100 ah 0x300 -A hmac-md5
0x96358c90783bbfa3d7b196ceabe0536b;

# ESP SAs using 192 bit long keys (168 + 24 parity)
add 192.168.1.100 192.168.2.100 esp 0x201 -E 3des-cbc
0x7aeaca3f87d060a12f4a4487d5a5c3355920fae69a96c831;
add 192.168.2.100 192.168.1.100 esp 0x301 -E 3des-cbc
0xf6ddb555acfd9d77b03ea3843f2653255afe8eb5573965df;

# Security policies
spdadd 192.168.1.100 192.168.2.100 any -P out ipsec
esp/transport//require
ah/transport//require;

spdadd 192.168.2.100 192.168.1.100 any -P in ipsec
esp/transport//require
ah/transport//require;

You will need some keys to replace the keys of this script, if you want to use the manually keyed connection for anything but testing purposes. Use a command such as the following to generate your keys:

$ # 128 Bit long key
$ dd if=/dev/random count=16 bs=1| xxd -ps
16+0 Records ein
16+0 Records aus
cd0456eff95c5529ea9e918043e19cbe

$ # 192 Bit long key
$ dd if=/dev/random count=24 bs=1| xxd -ps
24+0 Records ein
24+0 Records aus
9d6c4a8275ab12fbfdcaf01f0ba9dcfb5f424c878e97f888

Please use the device /dev/random when generating the keys because it ensures random keys.

The script first flushes the security association database (SAD) and the security policy database (SPD). It then creates AH SAs and ESP SAs. The command add adds a security association to the SAD and requires the source and destination IP address, the IPsec protocol (ah), the SPI (0x200) and the algorithm. The authentication algorithm is specified with -A (encryption using -E, compression using -C; IP compression is not yet supported). Following the algorithm the key must be specified. The key may be formatted in double-quoted “ASCII” or in hexadecimal with a leading 0x.

Linux supports the following algorithms for AH and ESP: hmac-md5 and hmac-sha, des-cbc and 3des-cbc. Within a short amount of time the following algorithms will probably be supported: simple (no encryption), blowfish-cbc, aes-cbc, hmac-sha2-256 and hmac-sha2-512.

spdadd adds the security policies to the SPD. These policies define which packets are to be protected by IPsec and which protocols and keys to use. The command requires the source and destination IP addresses of the packets to be protected, the protocol (and port) to protect (any) and the policy to use (-P). The policy specifies the direction (in/out), the action to apply (ipsec/discard/none), the protocol (ah/esp/ipcomp), the mode (transport) and the level (use/require).

This configuration file has to be created on both peers taking part in the IPsec communication. While the shown listing works without any change on the peer 192.168.1.100 it has to be slightly modified on the peer 192.168.2.100 to reflect the change of direction of the packets. The easiest way to do it is to exchange the directions in the security policies: replace -P in with -P out and vice versa. This is shown in the following listing:

#!/usr/sbin/setkey -f

# Configuration for 192.168.2.100

# Flush the SAD and SPD
flush;
spdflush;

# Attention: Use this keys only for testing purposes!
# Generate your own keys!

# Security policies
spdadd 192.168.1.100 192.168.2.100 any -P in ipsec
esp/transport//require
ah/transport//require;

spdadd 192.168.2.100 192.168.1.100 any -P out ipsec
esp/transport//require
ah/transport//require;

Once the configuration file is in place on the peers it can be loaded using setkey -f /etc/setkey.conf. The successful load can be tested by displaying the SAD and the SPD:

# setkey -D
# setkey -DP

If you now ping from one peer to the other the traffic will be encrypted and tcpdump will show the following packets:

12:45:39.373005 192.168.1.100 > 192.168.2.100: AH(spi=0x00000200,seq=0x1):
ESP(spi=0x00000201,seq=0x1) (DF)
12:45:39.448636 192.168.2.100 > 192.168.1.100: AH(spi=0x00000300,seq=0x1):
ESP(spi=0x00000301,seq=0x1)
12:45:40.542430 192.168.1.100 > 192.168.2.100: AH(spi=0x00000200,seq=0x2):
ESP(spi=0x00000201,seq=0x2) (DF)
12:45:40.569414 192.168.2.100 > 192.168.1.100: AH(spi=0x00000300,seq=0x2):
ESP(spi=0x00000301,seq=0x2)

1. ipsec-tools on ubuntu14.04

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