- Start packet capture in GUI -> Network -> Packet Capture.
 - Follow the commands on FortiGate to extract the encryption key to decrypt the Phase-2 packet on Wireshark.
- Clear the existing ike SA (# diag vpn ike gateway clear name <name>).
- Initiate traffic to trigger the ike/ipsec SA.
- Get the SPI and ISAKMP keys from FortiGate (# diag vpn ike gateway).
 - ISAKMP keys can be obtained in IKE Debug.
diagnose debug console timestamp enable diagnose vpn ike log-filter dst-addr4 <Remote Gateway IP> <----- Change <Remote Gateway IP>. diagnose debug application ike -1
diagnose debug enable For v7.4.0 and above: diagnose debug console timestamp enable diagnose vpn ike log filter rem-addr4 <Remote Gateway IP> <----- Change <Remote Gateway IP>.
diagnose debug application ike -1
diagnose debug enable Responder: ike V=root:0:Test:150: sent IKE msg (SA_INIT_RESPONSE): x.x.x.x:500->x.x.x.x:500, len=240, vrf=0, id=4de3c0f28601422e/a46da21febd5e243, oif=6
ike 0:Test:150: IKE SA 4de3c0f28601422e/a46da21febd5e243 SK_ei 16:63A4C02A86C7F3B33658166E4C4541A7
ike 0:Test:150: IKE SA 4de3c0f28601422e/a46da21febd5e243 SK_er 16:AE9B5748FC702FD48604E4912785BE72
ike 0:Test:150: IKE SA 4de3c0f28601422e/a46da21febd5e243 SK_ai 32:7254658FA96D17062AC0CE142D81708D8E12BDF96BAA749EACF0624035F62E8D
ike 0:Test:150: IKE SA 4de3c0f28601422e/a46da21febd5e243 SK_ar 32:90DB1576CAAF621AD7CD4884121FB5213A52C380C3DEB095CF9ADE8E76D64C27 Initiator: ike 0:Test:227884: initiator received SA_INIT response
.......
ike 0:Test:227884: IKE SA 4de3c0f28601422e/a46da21febd5e243 SK_ei 16:63A4C02A86C7F3B33658166E4C4541A7
ike 0:Test:227884: IKE SA 4de3c0f28601422e/a46da21febd5e243 SK_er 16:AE9B5748FC702FD48604E4912785BE72
ike 0:Test:227884: IKE SA 4de3c0f28601422e/a46da21febd5e243 SK_ai 32:7254658FA96D17062AC0CE142D81708D8E12BDF96BAA749EACF0624035F62E8D
ike 0:Test:227884: IKE SA 4de3c0f28601422e/a46da21febd5e243 SK_ar 32:90DB1576CAAF621AD7CD4884121FB5213A52C380C3DEB095CF9ADE8E76D64C27 - Stop packet capture and download the TAR file.
- Open the downloaded PCAP file on Wireshark.
Make sure that SPI in CLI output and Wireshark capture are the same. The screenshot below shows encrypted data.  - Select ISAKMP phase2 packet -> Protocol preferences -> Internet Security Association and Key Management Protocol -> IKEv2 Decryption table.
- A New Wireshark window will pop up as below.
Add a new row by selecting+ sign, select the field to fill the values from FortiGate Cli (SPI, SK_ei, SK_er, SK_ai, SK_ar). Note: remove the '–' before entering the values.   - After completing 6., the decrypted phase-2 packet will be viewable.
 - Decrypted phase-2 packets when phase 2 is up.
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