Thank you very much, Muhammad I tried reducing the SSL key bit length to 1024 but the buffer is still less than the key size. Hence, I submitted an issue with signalwire. I appreciate your help.  Regards *Maharaja Azhagiah* On Mon, Jun 27, 2022 at 10:05 PM M S &lt;shaheryarkh(a)gmail.com&gt; wrote: This error is  seems to come from libstirshaken (https://github.com/signalwire/libstirshaken/blob/master/include/stir_shaken… line 46) and has nothing to do with Kamailio. Please open a bug with signalwire who owns and maintains this library. Per my understanding this library is bit old and uses many deprecated functions and needs updating. As a general rule of thumb, in PEM format, the private key size in bytes is roughly 80% (4/5) of key size in bits e.g. 4096 bit private key size would be roughly, (4096 * 4) / 5 ~= 3277 byes which is too big for allowed size (2000 byes) in libstirshaken. So, either increasing the allowed size in libstirshaken OR reducing your SSL key bit length to e.g. 1024 may work. Thank you. -- Muhammad Shahzad Shafi Tel: +49 176 99 83 10 85 On Mon, Jun 27, 2022 at 11:07 PM Maharaja Azhagiah &lt;er.maharaja(a)gmail.com&gt; wrote: Hi, I am trying STIR/SHAKEN using libstirshaken in Kamailio 5.5. I used a self signed certificate as this is just a test in the local docker environment. However, when I try to add identity with private key (stirshaken_add_identity_with_key), I get "[error_code: 447] Buffer for key from file /tmp/cert/private.pem too short (2000 <= 3247)" I have tried using 2048 and 4096 size root@5907e44bd056:/tmp/cert# openssl rsa -in private.pem -text -noout | grep "Private-Key" RSA Private-Key: (4096 bit, 2 primes) Could you tell me what is wrong with the certificate? Kamailio version: root@5907e44bd056:/usr/local/kamailio/etc/kamailio# kamailio -v version: kamailio 5.5.4 (x86_64/linux) 469465 Error:  0(404) ERROR: {1 30587 INVITE NzIhM1-2YABveZZ1mPvs3m3tw8K7meSq} stirshaken [stirshaken_mod.c:761]: ki_stirshaken_add_identity_with_key(): Failed to load private key  0(404) DEBUG: {1 30587 INVITE NzIhM1-2YABveZZ1mPvs3m3tw8K7meSq} stirshaken [stirshaken_mod.c:117]: stirshaken_print_error_details(): failure details:  0(404) DEBUG: {1 30587 INVITE NzIhM1-2YABveZZ1mPvs3m3tw8K7meSq} stirshaken [stirshaken_mod.c:118]: stirshaken_print_error_details(): failure reason is: src/stir_shaken_ssl.c:2112: [error_code: 447] Buffer for key from file /tmp/cert/private.pem too short (2000 <= 3247)  0(404) DEBUG: {1 30587 INVITE NzIhM1-2YABveZZ1mPvs3m3tw8K7meSq} stirshaken [stirshaken_mod.c:119]: stirshaken_print_error_details(): failure error code is: 447  0(404) ERROR: {1 30587 INVITE NzIhM1-2YABveZZ1mPvs3m3tw8K7meSq} <script>: Failed Regards *Maharaja Azhagiah* __________________________________________________________ Kamailio - Users Mailing List - Non Commercial Discussions   * sr-users(a)lists.kamailio.org Important: keep the mailing list in the recipients, do not reply only to the sender! Edit mailing list options or unsubscribe:   * https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users __________________________________________________________ Kamailio - Users Mailing List - Non Commercial Discussions   * sr-users(a)lists.kamailio.org Important: keep the mailing list in the recipients, do not reply only to the sender! Edit mailing list options or unsubscribe:   * https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users __________________________________________________________ Kamailio - Users Mailing List - Non Commercial Discussions * sr-users(a)lists.kamailio.org Important: keep the mailing list in the recipients, do not reply only to the sender! Edit mailing list options or unsubscribe: * https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users