diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 233a2c7..563d86e 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -338,14 +338,14 @@
 server5-tricky-ip-san.crt: server5.key
 	$(OPENSSL) req -x509 -new -subj "/C=UK/O=Mbed TLS/CN=Mbed TLS Tricky IP SAN" -set_serial 77 -config $(test_ca_config_file) -extensions tricky_ip_san -days 3650 -sha256 -key server5.key -out $@
 	
-server5-directoryname.crt: server5.key
-	$(OPENSSL) req -x509 -new -subj "/C=UK/O=Mbed TLS/CN=Mbed TLS directoryName SAN" -set_serial 77 -config $(test_ca_config_file) -extensions directory_name_san -days 3650 -sha256 -key server5.key -out $@
+server5-directoryname.crt.der: server5.key
+	$(OPENSSL) req -x509 -outform der -new -subj "/C=UK/O=Mbed TLS/CN=Mbed TLS directoryName SAN" -set_serial 77 -config $(test_ca_config_file) -extensions directory_name_san -days 3650 -sha256 -key server5.key -out $@
 
-server5-two-directorynames.crt: server5.key
-	$(OPENSSL) req -x509 -new -subj "/C=UK/O=Mbed TLS/CN=Mbed TLS directoryName SAN" -set_serial 77 -config $(test_ca_config_file) -extensions two_directorynames -days 3650 -sha256 -key server5.key -out $@
+server5-two-directorynames.crt.der: server5.key
+	$(OPENSSL) req -x509 -outform der -new -subj "/C=UK/O=Mbed TLS/CN=Mbed TLS directoryName SAN" -set_serial 77 -config $(test_ca_config_file) -extensions two_directorynames -days 3650 -sha256 -key server5.key -out $@
 
-server5-second-directoryname-malformed.crt: server5-two-directorynames.crt
-	(head -n1 $<; sed -n '2,12p' $< | base64 --decode | hexdump -ve '1/1 "%.2X"' | sed "s/0355040A0C0A4D414C464F524D5F4D45/1555040A0C0A4D414C464F524D5F4D45/" | xxd -r -p | base64 -w64; tail -n1 $<) > $@
+server5-second-directoryname-malformed.crt.der: server5-two-directorynames.crt.der
+	hexdump -ve '1/1 "%.2X"' $< | sed "s/0355040A0C0A4D414C464F524D5F4D45/1555040A0C0A4D414C464F524D5F4D45/" | xxd -r -p > $@
 
 all_final += server5-tricky-ip-san.crt
 
diff --git a/tests/data_files/server5-directoryname.crt b/tests/data_files/server5-directoryname.crt
deleted file mode 100644
index afa88b3..0000000
--- a/tests/data_files/server5-directoryname.crt
+++ /dev/null
@@ -1,13 +0,0 @@
------BEGIN CERTIFICATE-----
-MIIB7jCCAZSgAwIBAgIBTTAKBggqhkjOPQQDAjBFMQswCQYDVQQGEwJVSzERMA8G
-A1UECgwITWJlZCBUTFMxIzAhBgNVBAMMGk1iZWQgVExTIGRpcmVjdG9yeU5hbWUg
-U0FOMB4XDTIzMDExMDE2NTkyOVoXDTMzMDEwNzE2NTkyOVowRTELMAkGA1UEBhMC
-VUsxETAPBgNVBAoMCE1iZWQgVExTMSMwIQYDVQQDDBpNYmVkIFRMUyBkaXJlY3Rv
-cnlOYW1lIFNBTjBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABDfMVtl2CR5acj7H
-WS3/IG7ufPkGkXTQrRS192giWWKSTuUA2CMR/+ov0jRdXRa9iojCa3cNVc2KKg76
-Aci07f+jdTBzMFIGA1UdEQRLMEmkRzBFMQswCQYDVQQGEwJVSzERMA8GA1UECgwI
-TWJlZCBUTFMxIzAhBgNVBAMMGk1iZWQgVExTIGRpcmVjdG9yeU5hbWUgU0FOMB0G
-A1UdDgQWBBRQYaWP1AfZ14IBDOVlf4xjRqcTvjAKBggqhkjOPQQDAgNIADBFAiBr
-PtyaL8tF+jghNK32ZnWriCp2k7Aq+QVuef+6+sSH6AIhAIKw+o0J2Pu27ulHFIzI
-MdFECpZ3nqAGbTOTOMX6LoDh
------END CERTIFICATE-----
diff --git a/tests/data_files/server5-directoryname.crt.der b/tests/data_files/server5-directoryname.crt.der
new file mode 100644
index 0000000..4badea1
--- /dev/null
+++ b/tests/data_files/server5-directoryname.crt.der
Binary files differ
diff --git a/tests/data_files/server5-second-directoryname-malformed.crt b/tests/data_files/server5-second-directoryname-malformed.crt
deleted file mode 100644
index 11d439b..0000000
--- a/tests/data_files/server5-second-directoryname-malformed.crt
+++ /dev/null
@@ -1,13 +0,0 @@
------BEGIN CERTIFICATE-----
-MIICCTCCAa+gAwIBAgIBTTAKBggqhkjOPQQDAjBFMQswCQYDVQQGEwJVSzERMA8G
-A1UECgwITWJlZCBUTFMxIzAhBgNVBAMMGk1iZWQgVExTIGRpcmVjdG9yeU5hbWUg
-U0FOMB4XDTIzMDExMjEwMzQxMVoXDTMzMDEwOTEwMzQxMVowRTELMAkGA1UEBhMC
-VUsxETAPBgNVBAoMCE1iZWQgVExTMSMwIQYDVQQDDBpNYmVkIFRMUyBkaXJlY3Rv
-cnlOYW1lIFNBTjBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABDfMVtl2CR5acj7H
-WS3/IG7ufPkGkXTQrRS192giWWKSTuUA2CMR/+ov0jRdXRa9iojCa3cNVc2KKg76
-Aci07f+jgY8wgYwwawYDVR0RBGQwYqRHMEUxCzAJBgNVBAYTAlVLMREwDwYDVQQK
-DAhNYmVkIFRMUzEjMCEGA1UEAwwaTWJlZCBUTFMgZGlyZWN0b3J5TmFtZSBTQU6k
-FzAVMRMwEQYVVQQKDApNQUxGT1JNX01FMB0GA1UdDgQWBBRQYaWP1AfZ14IBDOVl
-f4xjRqcTvjAKBggqhkjOPQQDAgNIADBFAiAHI/ousygMhcDhAb+bK402vAh4+bGK
-UuwPMpd1XQ2FHAIhAL0uuCTzI72PJLyxB4cFtbmodUejDc+Oa02AUW4Ed8Uu
------END CERTIFICATE-----
diff --git a/tests/data_files/server5-second-directoryname-malformed.crt.der b/tests/data_files/server5-second-directoryname-malformed.crt.der
new file mode 100644
index 0000000..7074fd8
--- /dev/null
+++ b/tests/data_files/server5-second-directoryname-malformed.crt.der
Binary files differ
diff --git a/tests/data_files/server5-two-directorynames.crt b/tests/data_files/server5-two-directorynames.crt
deleted file mode 100644
index aa76c16..0000000
--- a/tests/data_files/server5-two-directorynames.crt
+++ /dev/null
@@ -1,13 +0,0 @@
------BEGIN CERTIFICATE-----
-MIICCTCCAa+gAwIBAgIBTTAKBggqhkjOPQQDAjBFMQswCQYDVQQGEwJVSzERMA8G
-A1UECgwITWJlZCBUTFMxIzAhBgNVBAMMGk1iZWQgVExTIGRpcmVjdG9yeU5hbWUg
-U0FOMB4XDTIzMDExMjEwMzQxMVoXDTMzMDEwOTEwMzQxMVowRTELMAkGA1UEBhMC
-VUsxETAPBgNVBAoMCE1iZWQgVExTMSMwIQYDVQQDDBpNYmVkIFRMUyBkaXJlY3Rv
-cnlOYW1lIFNBTjBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABDfMVtl2CR5acj7H
-WS3/IG7ufPkGkXTQrRS192giWWKSTuUA2CMR/+ov0jRdXRa9iojCa3cNVc2KKg76
-Aci07f+jgY8wgYwwawYDVR0RBGQwYqRHMEUxCzAJBgNVBAYTAlVLMREwDwYDVQQK
-DAhNYmVkIFRMUzEjMCEGA1UEAwwaTWJlZCBUTFMgZGlyZWN0b3J5TmFtZSBTQU6k
-FzAVMRMwEQYDVQQKDApNQUxGT1JNX01FMB0GA1UdDgQWBBRQYaWP1AfZ14IBDOVl
-f4xjRqcTvjAKBggqhkjOPQQDAgNIADBFAiAHI/ousygMhcDhAb+bK402vAh4+bGK
-UuwPMpd1XQ2FHAIhAL0uuCTzI72PJLyxB4cFtbmodUejDc+Oa02AUW4Ed8Uu
------END CERTIFICATE-----
diff --git a/tests/data_files/server5-two-directorynames.crt.der b/tests/data_files/server5-two-directorynames.crt.der
new file mode 100644
index 0000000..c98a018
--- /dev/null
+++ b/tests/data_files/server5-two-directorynames.crt.der
Binary files differ