diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 40cbcbe..05d7d23 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -104,7 +104,7 @@
 	$(FAKETIME) -f +3653d $(OPENSSL) x509 -req -extfile $(cli_crt_extensions_file) -extensions cli-rsa -CA $(test_ca_int_rsa1) -CAkey test-int-ca.key -set_serial 16 -days 3653 -sha256 -in server7.csr | cat - $(test_ca_int_rsa1) > $@
 all_final += server7-future.crt
 server7-badsign.crt: server7.crt $(test_ca_int_rsa1)
-	{ head -n-2 server7.crt; tail -n-2 server7.crt | sed -e '1s/0\(=*\)$$/_\1/' -e '1s/[^_=]\(=*\)$$/0\1/' -e '1s/_/1/'; cat test-int-ca.crt; } > server7-badsign.crt
+	{ head -n-2 $<; tail -n-2 $< | sed -e '1s/0\(=*\)$$/_\1/' -e '1s/[^_=]\(=*\)$$/0\1/' -e '1s/_/1/'; cat $(test_ca_int_rsa1); } > $@
 all_final += server7-badsign.crt
 server7_int-ca-exp.crt: server7.crt test-int-ca-exp.crt
 	cat server7.crt test-int-ca-exp.crt > $@
@@ -119,7 +119,18 @@
 	$(FAKETIME) '2015-09-01 14:08:43' $(OPENSSL) req -x509 -new -subj "/C=UK/O=mbed TLS/CN=mbed TLS Test intermediate CA 3" -set_serial 77 -config $(test_ca_config_file) -extensions noext_ca -days 3650 -sha256 -key $< -out $@
 all_final += server5-ss-forgeca.crt
 
-
+server10-badsign.crt: server10.crt
+	{ head -n-2 $<; tail -n-2 $< | sed -e '1s/0\(=*\)$$/_\1/' -e '1s/[^_=]\(=*\)$$/0\1/' -e '1s/_/1/'; } > $@
+all_final += server10-badsign.crt
+server10-bs_int3.pem: server10-badsign.crt test-int-ca3.crt
+	cat server10-badsign.crt test-int-ca3.crt > $@
+all_final += server10-bs_int3.pem
+test-int-ca3-badsign.crt: test-int-ca3.crt
+	{ head -n-2 $<; tail -n-2 $< | sed -e '1s/0\(=*\)$$/_\1/' -e '1s/[^_=]\(=*\)$$/0\1/' -e '1s/_/1/'; } > $@
+all_final += test-int-ca3-badsign.crt
+server10_int3-bs.pem: server10.crt test-int-ca3-badsign.crt
+	cat server10.crt test-int-ca3-badsign.crt > $@
+all_final += server10-bs_int3-bs.pem
 
 
 ################################################################
diff --git a/tests/data_files/Readme-x509.txt b/tests/data_files/Readme-x509.txt
index b56346a..d1a6c2d 100644
--- a/tests/data_files/Readme-x509.txt
+++ b/tests/data_files/Readme-x509.txt
@@ -21,6 +21,7 @@
 
 A third intermediate CA is signed by test-int-ca2.crt:
 - test-int-ca3.crt "C=UK, O=mbed TLS, CN=mbed TLS Test intermediate CA 3"
+  uses an EC key with NIST P-256, signed by test-int-ca2
 
 Finally, other CAs for specific purposes:
 - enco-ca-prstr.pem: has its CN encoded as a printable string, but child cert
diff --git a/tests/data_files/server10-badsign.crt b/tests/data_files/server10-badsign.crt
new file mode 100644
index 0000000..eca171f
--- /dev/null
+++ b/tests/data_files/server10-badsign.crt
@@ -0,0 +1,10 @@
+-----BEGIN CERTIFICATE-----
+MIIBWjCCAQCgAwIBAgIBSzAKBggqhkjOPQQDAjBKMQswCQYDVQQGEwJVSzERMA8G
+A1UEChMIbWJlZCBUTFMxKDAmBgNVBAMTH21iZWQgVExTIFRlc3QgaW50ZXJtZWRp
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+AzO3pJx7WJAApZuBX10=
+-----END CERTIFICATE-----
diff --git a/tests/data_files/server10-bs_int3.pem b/tests/data_files/server10-bs_int3.pem
new file mode 100644
index 0000000..b84cee7
--- /dev/null
+++ b/tests/data_files/server10-bs_int3.pem
@@ -0,0 +1,22 @@
+-----BEGIN CERTIFICATE-----
+MIIBWjCCAQCgAwIBAgIBSzAKBggqhkjOPQQDAjBKMQswCQYDVQQGEwJVSzERMA8G
+A1UEChMIbWJlZCBUTFMxKDAmBgNVBAMTH21iZWQgVExTIFRlc3QgaW50ZXJtZWRp
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+oZyychmoCRxzrd4Vu96m47NPBehtEC46aTeXgDnBdf++znABrAtfXBRNQz8ARIeY
+Bmskr22rlKjyow0wCzAJBgNVHRMEAjAAMAoGCCqGSM49BAMCA0gAMEUCIQDLc+Io
+rg8VxEbCgVv8iH+kOIEn9MjhpvKzvwUoV+6rjQIgZU/RXAyc1a+H2+soGfNEIOBQ
+AzO3pJx7WJAApZuBX10=
+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----
+MIIBtDCCATqgAwIBAgIBTTAKBggqhkjOPQQDAjBLMQswCQYDVQQGEwJOTDERMA8G
+A1UEChMIUG9sYXJTU0wxKTAnBgNVBAMTIFBvbGFyU1NMIFRlc3QgSW50ZXJtZWRp
+YXRlIEVDIENBMB4XDTE1MDkwMTE0MDg0M1oXDTI1MDgyOTE0MDg0M1owSjELMAkG
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+Qh7CK80CMQD7wa1o1a8qyDKBfLN636uKmKGga0E+vYXBeFCy9oARBangGCB0B2vt
+pz590JvGWfM=
+-----END CERTIFICATE-----
diff --git a/tests/data_files/server10.crt b/tests/data_files/server10.crt
new file mode 100644
index 0000000..96a4040
--- /dev/null
+++ b/tests/data_files/server10.crt
@@ -0,0 +1,10 @@
+-----BEGIN CERTIFICATE-----
+MIIBWjCCAQCgAwIBAgIBSzAKBggqhkjOPQQDAjBKMQswCQYDVQQGEwJVSzERMA8G
+A1UEChMIbWJlZCBUTFMxKDAmBgNVBAMTH21iZWQgVExTIFRlc3QgaW50ZXJtZWRp
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+AzO3pJx7WJAApZuBX1Q=
+-----END CERTIFICATE-----
diff --git a/tests/data_files/server10_int3-bs.pem b/tests/data_files/server10_int3-bs.pem
new file mode 100644
index 0000000..a9e0615
--- /dev/null
+++ b/tests/data_files/server10_int3-bs.pem
@@ -0,0 +1,22 @@
+-----BEGIN CERTIFICATE-----
+MIIBWjCCAQCgAwIBAgIBSzAKBggqhkjOPQQDAjBKMQswCQYDVQQGEwJVSzERMA8G
+A1UEChMIbWJlZCBUTFMxKDAmBgNVBAMTH21iZWQgVExTIFRlc3QgaW50ZXJtZWRp
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+AzO3pJx7WJAApZuBX1Q=
+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----
+MIIBtDCCATqgAwIBAgIBTTAKBggqhkjOPQQDAjBLMQswCQYDVQQGEwJOTDERMA8G
+A1UEChMIUG9sYXJTU0wxKTAnBgNVBAMTIFBvbGFyU1NMIFRlc3QgSW50ZXJtZWRp
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+Qh7CK80CMQD7wa1o1a8qyDKBfLN636uKmKGga0E+vYXBeFCy9oARBangGCB0B2vt
+pz590JvGWf0=
+-----END CERTIFICATE-----
diff --git a/tests/data_files/test-int-ca3-badsign.crt b/tests/data_files/test-int-ca3-badsign.crt
new file mode 100644
index 0000000..2087056
--- /dev/null
+++ b/tests/data_files/test-int-ca3-badsign.crt
@@ -0,0 +1,12 @@
+-----BEGIN CERTIFICATE-----
+MIIBtDCCATqgAwIBAgIBTTAKBggqhkjOPQQDAjBLMQswCQYDVQQGEwJOTDERMA8G
+A1UEChMIUG9sYXJTU0wxKTAnBgNVBAMTIFBvbGFyU1NMIFRlc3QgSW50ZXJtZWRp
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+pz590JvGWf0=
+-----END CERTIFICATE-----