/* de-cryption to get the client random number */
mbedtls_aes_init(&aes);
mbedtls_aes_setkey_enc(&aes, key_encrypt, 128); /* do not use mbedtls_aes_setkey_dec(&aes, key_encrypt, 128); */
offset = 0;

input[0] = 0xbb;
input[1] = 0x83;
input[2] = 0xe0;
input[3] = 0x37;
input[4] = 0x8d;
input ...