IPsec with public key authentication on Mikrotik RouterOS

Setup

Generate an RSA keypair

[admin@mtk1] > /ip ipsec key
[admin@mtk1] /ip ipsec key> generate-key mykey key-size=4096
For key bigger than 1024bit this may take a while..
[admin@mtk1] /ip ipsec key> print
Flags: P - private-key, R - rsa
 #    NAME                                                             KEY-SIZE
 0 PR mykey                                                            4096-bit

Exchange public keys with your peer

  1. Export the public key to a file.

     [admin@mtk1] /ip ipsec key> export-pub-key mykey file-name=mykey.pub

 [admin@mtk1] /ip ipsec key> /file print where name=mykey.pub
  # NAME                   TYPE                        SIZE CREATION-TIME
  2 mykey.pub              ssh key                      451 jul/20/2014 12:35:33

  2. Copy the file to your workstation and send it to your peer. The contents of the file should look like this:

     -----BEGIN PUBLIC KEY-----
 MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAv4RHohMZP4F5qTJKqoSL
 TqefoZZRt1RVI5dOocjV1pJZnqcXMtHfQ/5+O+igUCAX+yBv0hie+U32FWcy5cQO
 +xaohZW1zFzvlRWVqOpTwdk/993Zmy070T1FzK4kFShsNtxYrtYNheCnakgfXgMg
 23w/35zcof64/ewzF6RuqkTzmccIFCWDuv2IobXTOYAk7G3PGN4xWscvFIroIy5s
 4E8oOmKWVoFErQA6XetJzI+X+knzI3J/6/Pff4Tz7TLxu1m2I0InFaBv1G0+BXnh
 QOvIM7fvs5s0YWaUdT+vz8F0SHtb6Q/IdWc4JJPH/Q2t4HKTkk7FUnvvub2GxVbs
 8QIDAQAB
 -----END PUBLIC KEY-----

  3. Convert your peer's public key to the PEM format using the pubkey-converter script, if necessary.

Configuration

Configure the phase 1 IKE parameters

In this example, we'll use the following settings:

Key Value
Encryption AES-128
Hash HMAC-SHA1
DH Group 5 (modp1536)
Lifetime 28800 seconds
Peer address 192.0.2.2
Local address 192.0.2.1

  1. Copy your peer's PEM-encoded public key to the router and import it. (Hit enter when it asks for a passphrase)

     [admin@mtk1] /ip ipsec key> import peer-key.pub name=peer-key
 passphrase:

 [admin@mtk1] /ip ipsec key> print
 Flags: P - private-key, R - rsa
  #    NAME                                                             KEY-SIZE
  0 PR mykey                                                            4096-bit
  1  R peer-key                                                         4096-bit

  2. Configure your peer definition to use the public key

     [admin@mtk1] /ip ipsec peer> add address=192.0.2.2 local-address=192.0.2.1 enc-algorithm=aes-128 hash-algorithm=sha1 dh-group=modp1536 lifetime=28800 key=mykey remote-key=peer-key auth-method=rsa-key
 [admin@mtk1] /ip ipsec peer> print
 Flags: X - disabled
  0   address=192.0.2.2/32 local-address=192.0.2.1 passive=no port=500
      auth-method=rsa-key key=mykey remote-key=peer-key generate-policy=no
      exchange-mode=main send-initial-contact=yes nat-traversal=no
      proposal-check=obey hash-algorithm=sha1 enc-algorithm=aes-128
      dh-group=modp1536 lifetime=8h lifebytes=0 dpd-interval=2m
      dpd-maximum-failures=5

  3. All done! Configure the phase 2 parameters as you otherwise would.

Full GRE/IPsec example

# jul/20/2014 13:00:04 by RouterOS 6.15
# software id = HBCA-0B2J
#
/interface gre
add dscp=inherit local-address=192.0.2.1 mtu=1400 name=gre-tunnel1 \
    remote-address=192.0.2.2
/ip address
add address=10.1.2.0/31 interface=gre-tunnel1 network=10.1.2.0
/ip ipsec proposal
set [ find default=yes ] lifetime=1h pfs-group=modp1536
/ip ipsec peer
add address=192.0.2.2/32 auth-method=rsa-key dh-group=modp1536 key=mykey \
    lifetime=8h local-address=192.0.2.1 remote-key=peer-key
/ip ipsec policy
add dst-address=192.0.2.2/32 protocol=gre sa-dst-address=192.0.2.2 \
    sa-src-address=192.0.2.1 src-address=192.0.2.1/32