Using a DER encoded cert


I have looked else where on site but cannot find the information I need. I am trying to connect to a server using SSL. The server is using a Let’sEncypt root cert.
This is an embedded project using an STM32F407 and a CC3100. The CC3100 requires a DER encoded cert with I have downloaded from your site. I am using cipher SL_SEC_MASK_SSL_RSA_WITH_RC4_128_SHA and method SL_SO_SEC_METHOD_SSLV3. The error returned is -155 which is incorrect cert. Can anybody help with this? I have successfully connected to google dot com using a different cert.

Am I using the correct cipher SL_SEC_MASK_SSL_RSA_WITH_RC4_128_SHA ?
Am I using the correct method SL_SO_SEC_METHOD_SSLV3 ?
Has anybody used the letsencrypt DER encoded cert successfully?



To answer my own question, the problem appears to be with the CC3100 firmware, if I don’t try to verify the server, then I can connect but with error -453 connected but with server not verified. This I can work with at the moment, but I will raise the question on the TI forum.