To Configure TLS between Integrator and Gateway, Follow the below steps-

A. Check cstcp configuration for Gateway with command-
peluconf standalone get -s cstcp

[cstcp]active='1'
[cstcp]auto_control='2'
[cstcp]HostName=''
[cstcp]Port='18770'
[cstcp]TlsActive='0'
[cstcp]TlsCipherSuite='TLS_RSA_ANON_WITH_AES_128_CBC_SHA'
[cstcp]Trace='4'
[cstcp]ServerMax='10'
[cstcp]cstcp_command='ipelapid.sock -tpt CSTCP'
[cstcp]cstcp_context_file='$p_database/cstcpctx.dat'
[cstcp]TlsServerCertificateFile=''
[cstcp]TlsPasswordDkFile=''
[cstcp]TlsPasswordEncFile=''

TlsActive='0' shows TLS is not enabled at Gateway server.

Similarly check $CORE_LOCAL/bin/csconfig.ini file ( for TlsActive entry) to verify if TLS is enabled/disabled in Integrator.

B. Execute below command to generate gateway's file for certificate's password
pelencpass encrypt_pass -encis axway -encpwd 'Certificate_Password' -saltf /Gateway_V6.17/run_time/tls/salt_key_file -dkf /Gateway_V6.17/run_time/tls/derived_key_file -encf //Gateway_V6.17/run_time/tls/encrypted_data_file

C. Update Gateway's CSTCP configuration with below commands-

1. peluconf standalone set -s cstcp TlsServerCertificateFile /Gateway_V6.17/run_time/tls/Axway_SPHERE_GTW_Navigator.p12
2. peluconf standalone set -s cstcp TlsPasswordDkFile /Gateway_V6.17/run_time/tls/derived_key_file
3. peluconf standalone set -s cstcp TlsPasswordEncFile /Gateway_V6.17/run_time/tls/encrypted_data_file
4. peluconf standalone set -s cstcp TlsCipherSuite TLS_RSA_WITH_AES_128_CBC_SHA
5. peluconf standalone set -s cstcp TlsActive 1
6. peluconf standalone set -s cstcp Trace 4

new CSTCP configuration is-
[cstcp]active='1'
[cstcp]auto_control='2'
[cstcp]HostName=''
[cstcp]Port='18770'
[cstcp]TlsActive='1'
[cstcp]TlsCipherSuite='TLS_RSA_WITH_AES_128_CBC_SHA'
[cstcp]Trace='0'
[cstcp]ServerMax='10'
[cstcp]cstcp_command='ipelapid.sock -tpt CSTCP'
[cstcp]cstcp_context_file='$p_database/cstcpctx.dat'
[cstcp]TlsServerCertificateFile='/home/bnpmcs/apps/xip1/gtw/Gateway_V6.17/run_time/tls/Axway_SPHERE_GTW_Navigator.p12'
[cstcp]TlsPasswordDkFile='/home/bnpmcs/apps/xip1/gtw/Gateway_V6.17/run_time/tls/derived_key_file'
[cstcp]TlsPasswordEncFile='/home/bnpmcs/apps/xip1/gtw/Gateway_V6.17/run_time/tls/encrypted_data_file'

D. Run below commands to make changes effective

1. peluconf standalone rebuild
2. Restart Gateway

E. Add below entries in Integrator/local/bin/csconfig.ini
TlsActive = 1
TlsCipherSuite = TLS_RSA_WITH_AES_128_CBC_SHA
TlsTrustedCertificate = /Gateway_V6.17/run_time/tls/SPHERE_ROOT_Certificate.pem

Now csconfig.ini file would be as
Integrator/local/bin > cat csconfig.ini
[LOGIN]
[International]
Language = english
[CSTCP]
Transport = TCP
Hostname = rs63
Port = 18770
TlsUsed = 0
SendTimeout = 120
RecvTimeout = 0
CloseTimeout = 0
IdleTimeout = 0
TlsActive = 1
TlsCipherSuite = TLS_RSA_WITH_AES_128_CBC_SHA
TlsTrustedCertificate = /Gateway_V6.17/run_time/tls/SPHERE_ROOT_Certificate.pem

Restart Integrator

Now Integrator and Gateway will communicate Securly using TLS.