Decrypting TLS 1.3 Traffic

1. Capture packets on FortiWeb, and enable diagnose debug flow at the same time as follows.

   FortiWeb# diagnose debug flow filter flow-detail 4

   FortiWeb# diagnose debug flow trace start

   FortiWeb# diagnose debug enable

   Please note:

   • Add filters when capturing packets on FortiWeb;

   • Do not add filters in diagnose commands as below if the back-end server provides SSL/TLS service, otherwise SSL keys cannot be displayed in diagnose output. It’s a known limitation while we’ll enhance it in future builds.

   • If you only wants to decrypt SSL traffic from clients to FortiWeb, below filters can be added

     diagnose debug flow filter client-ip 172.30.214.11

     diagnose debug flow filter server-ip 10.159.37.33

2. The keys can be also found in the diagnose debug output as follows. It’s a little different from that of TLS1.2 and before.

   [work 0][flow] ssn 5 policy SP_01 strm 0 dir 0 subclient 0 client 32 ssl handshake(172.30.212.177:1039->10.159.37.1:7002),ssl event:2

   [work 0][flow] ssn 5 policy SP_01 strm 0 dir 0 subclient 0 client 32 [ST-ssl-handshake], conn st 0x00000004

   tls1.3 ssl key (server):

   SERVER_HANDSHAKE_TRAFFIC_SECRET 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 a52744e732f1b328650b40653ea0d9845fa8726f79b19a6b6dbdf08ff24c735efc907e948a53709c0cf5ef2c7038c8af

   tls1.3 ssl key (server):

   CLIENT_HANDSHAKE_TRAFFIC_SECRET 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 e14368e33bd50ba4dd106d0a5018e8e145e112b9cdac6fd3e0455b2479399bbf8bc54ab0f522512f93170c754d32a9ad

   tls1.3 ssl key (server):

   EXPORTER_SECRET 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 31ccbf2227090eea6653d334f5fd9a08667292ac0a220e25f139270fde716a5a14f3b426ba0611b012b985e04028c178

   tls1.3 ssl key (server):

   SERVER_TRAFFIC_SECRET_0 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 0faae977ef5ba35accdac2b189eedefea4ccf7363fc78f6933569f42659f27ece1bdae43dff88a7da18b950e5d021505

   [conn lib]ssl handshake, state:1

   [work 0][flow] ssn 5 policy SP_01 strm 0 dir 0 subclient 0 client 32 ssl handshake(172.30.212.177:1039->10.159.37.1:7002),ssl event:2

   [work 0][flow] ssn 5 policy SP_01 strm 0 dir 0 subclient 0 client 32 [ST-ssl-handshake], conn st 0x00000004

   tls1.3 ssl key (server):

   CLIENT_TRAFFIC_SECRET_0 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 c06b9cb7332bd05f1761d6ba6621345aa73a018f5f5db2ddfeb160b3aec755f8a9a40fd30041232a3d37bfb93aff24bd

   [conn lib]ssl handshake, state:2

   The first column is tls1.3 secret label as below:

   CLIENT_EARLY_TRAFFIC_SECRET: client early traffic secret

   CLIENT_HANDSHAKE_TRAFFIC_SECRET:client handshake secret

   SERVER_HANDSHAKE_TRAFFIC_SECRET:server handshake secret

   CLIENT_TRAFFIC_SECRET_0: client application data secret

   SERVER_TRAFFIC_SECRET_0: server application data secret

3. Create a wireshark key file. The key file format is as follows with content retrieved from the diagnose output.

   root@ut:/home/test/keys# cat tls1.3_key.file

   SERVER_HANDSHAKE_TRAFFIC_SECRET 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 a52744e732f1b328650b40653ea0d9845fa8726f7

   9b19a6b6dbdf08ff24c735efc907e948a53709c0cf5ef2c7038c8af

   CLIENT_HANDSHAKE_TRAFFIC_SECRET 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 e14368e33bd50ba4dd106d0a5018e8e145e112b9c

   dac6fd3e0455b2479399bbf8bc54ab0f522512f93170c754d32a9ad

   EXPORTER_SECRET 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 31ccbf2227090eea6653d334f5fd9a08667292ac0a220e25f139270fd

   e716a5a14f3b426ba0611b012b985e04028c178

   SERVER_TRAFFIC_SECRET_0 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 0faae977ef5ba35accdac2b189eedefea4ccf7363fc78f693

   3569f42659f27ece1bdae43dff88a7da18b950e5d021505

   CLIENT_TRAFFIC_SECRET_0 72e61efe2594465bf79935093e9d73254e1cd2e67f0acee06379166af25be863 c06b9cb7332bd05f1761d6ba6621345aa73a018f5f5db2ddf

   eb160b3aec755f8a9a40fd30041232a3d37bfb93aff24bd

   SERVER_HANDSHAKE_TRAFFIC_SECRET 49e35b0c4ddf3e521e07d2fc660a271cff2b2b64317bd48f343a69eb57ce70b6 fe1eb5cef9ca293fbd4899612d89339e0d76a5426

   55ccb08c249d32e330bc8232a8572d9bdcea7bbfd002764df227458

   EXPORTER_SECRET 49e35b0c4ddf3e521e07d2fc660a271cff2b2b64317bd48f343a69eb57ce70b6 5549b723b72fb18c30cc25a8ce86f8b5afe1bcfa1ed9bb6c3b9584408

   ef6fdac0c6286083c4046c99433e0424724351c

   SERVER_TRAFFIC_SECRET_0 49e35b0c4ddf3e521e07d2fc660a271cff2b2b64317bd48f343a69eb57ce70b6 ba1bb94d8740f7609919b18ab0c09201ade62ed6f6d8687ad

   892bdcf00e3bbc2f6ee253e26cf005acdabc6e80d2a29c2

   CLIENT_HANDSHAKE_TRAFFIC_SECRET 49e35b0c4ddf3e521e07d2fc660a271cff2b2b64317bd48f343a69eb57ce70b6 6fc9d895b73d8e8f33461b043ab0239b757d734b8

   f1dde1a664d519792cddd82aed2f81cc892f4e01865f68785851cc3

   CLIENT_TRAFFIC_SECRET_0 49e35b0c4ddf3e521e07d2fc660a271cff2b2b64317bd48f343a69eb57ce70b6 d4f3118b685428e8d53f7bbd63c15baa8b9828a8af062d984

   1619fa2d6b076d27bb3735df598f06204f13918a7993218

   You can manually copy & save the these sections to a file, or use a Linux command to retrieve them in the FortiWeb backend shell or a Linux machine as follows:

   root@utma:/home/test# awk '/EXPORTER_SECRET|SERVER_HANDSHAKE_TRAFFIC_SECRET|SERVER_TRAFFIC_SECRET_0|CLIENT_HANDSHAKE_TRAFFIC_SECRET|CLIENT_TRAFFIC_SECRET_0/{print $1" "$2" "$3}' tls1.3_flow.log > tls1.3_key.file

4. Set wireshark: edit > preference > protocols > TLS: choose the key file “tls1.3_key.file” from "(Pre)-Master-Secret log filename". Then you’ll be able to see that decrypted HTTP traffic.