Add invalid key tests for curve SECP224K1

This curve has special arithmetic on 64 bit platforms and an untested
path lead to trying to free a buffer on the stack.

For the sake of completeness, a test case for a point with non-affine
coordinates has been added as well.
diff --git a/tests/suites/test_suite_ecp.data b/tests/suites/test_suite_ecp.data
index 1c858b5..a43e7d7 100644
--- a/tests/suites/test_suite_ecp.data
+++ b/tests/suites/test_suite_ecp.data
@@ -32,11 +32,19 @@
 
 ECP check pubkey Montgomery #1 (too big)
 depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
-ecp_check_pub_mx:MBEDTLS_ECP_DP_CURVE25519:"010000000000000000000000000000000000000000000000000000000000000000":MBEDTLS_ERR_ECP_INVALID_KEY
+ecp_check_pub:MBEDTLS_ECP_DP_CURVE25519:"010000000000000000000000000000000000000000000000000000000000000000":"0":"1":MBEDTLS_ERR_ECP_INVALID_KEY
 
 ECP check pubkey Montgomery #2 (biggest)
 depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
-ecp_check_pub_mx:MBEDTLS_ECP_DP_CURVE25519:"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF":0
+ecp_check_pub:MBEDTLS_ECP_DP_CURVE25519:"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF":"0":"1":0
+
+ECP check pubkey Koblitz #1 (point not on curve)
+depends_on:MBEDTLS_ECP_DP_SECP224K1_ENABLED
+ecp_check_pub:MBEDTLS_ECP_DP_SECP224K1:"E2000000000000BB3A13D43B323337383935321F0603551D":"100101FF040830060101FF02010A30220603551D0E041B04636FC0C0":"1":MBEDTLS_ERR_ECP_INVALID_KEY
+
+ECP check pubkey Koblitz #2 (coordinate not affine)
+depends_on:MBEDTLS_ECP_DP_SECP224K1_ENABLED
+ecp_check_pub:MBEDTLS_ECP_DP_SECP224K1:"E2000000000000BB3A13D43B323337383935321F0603551D":"100101FF040830060101FF02010A30220603551D0E041B04636FC0C0":"101":MBEDTLS_ERR_ECP_INVALID_KEY
 
 ECP write binary #0 (zero, bad format)
 depends_on:MBEDTLS_ECP_DP_SECP192R1_ENABLED
diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index afe61ec..99780c0 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -29,7 +29,7 @@
 /* END_CASE */
 
 /* BEGIN_CASE */
-void ecp_check_pub_mx( int grp_id, char *key_hex, int ret )
+void ecp_check_pub( int grp_id, char *x_hex, char *y_hex, char *z_hex, int ret )
 {
     mbedtls_ecp_group grp;
     mbedtls_ecp_point P;
@@ -39,8 +39,9 @@
 
     TEST_ASSERT( mbedtls_ecp_group_load( &grp, grp_id ) == 0 );
 
-    TEST_ASSERT( mbedtls_mpi_read_string( &P.X, 16, key_hex ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_lset( &P.Z, 1 ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_read_string( &P.X, 16, x_hex ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_read_string( &P.Y, 16, y_hex ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_read_string( &P.Z, 16, z_hex ) == 0 );
 
     TEST_ASSERT( mbedtls_ecp_check_pubkey( &grp, &P ) == ret );