Resolve PR review comments

1) Fix style comments
2) Fix typo in Makefile
3) Remove the `MBEDTLS_MD5_C` dependency from test data file,
as the used keys are not encrypted
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index bfcdc68..3e20f66 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -65,11 +65,19 @@
 all_final += server2-sha256.crt
 
 rsa_pkcs1_2048_public.pem: server8.key
-	$(OPENSSL)  rsa -in server8.key -outform PEM -RSAPublicKey_out -out $@
-all_final += rsa_pkcs8_2048_public.pem
+	$(OPENSSL)  rsa -in $< -outform PEM -RSAPublicKey_out -out $@
+all_final += rsa_pkcs1_2048_public.pem
 
 rsa_pkcs1_2048_public.der: rsa_pkcs1_2048_public.pem
-	$(OPENSSL) -RSAPublicKey_in -in rsa_pkcs1_2048_public.pem -outform DER -RSAPublicKey_out -out $@
+	$(OPENSSL) rsa -RSAPublicKey_in -in $< -outform DER -RSAPublicKey_out -out $@
+all_final += rsa_pkcs1_2048_public.der
+
+rsa_pkcs8_2048_public.pem: server8.key
+	$(OPENSSL)  rsa -in $< -outform PEM -pubout -out $@
+all_final += rsa_pkcs8_2048_public.pem
+
+rsa_pkcs8_2048_public.der: rsa_pkcs8_2048_public.pem
+	$(OPENSSL) rsa -pubin -in $< -outform DER -pubout -out $@
 all_final += rsa_pkcs8_2048_public.der
 
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