Add DoS test case for ecp_check_pub

A test case for which the loop would take practically forever if it was
reached. The point would be to validate that the loop is not reached.
The test case should cause the CI to time out if starting with the
current code, ecp_check_pubkey_mx() was changed to call
ecp_check_pubkey_x25519() first and run the mbedtls_mpi_size(() test
afterwards, which would make no semantic difference in terms of memory
contents when the function returns, but would open the way for a DoS.

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/tests/suites/test_suite_ecp.data b/tests/suites/test_suite_ecp.data
index 0b225be..5b513ab 100644
--- a/tests/suites/test_suite_ecp.data
+++ b/tests/suites/test_suite_ecp.data
@@ -33,13 +33,17 @@
 depends_on:MBEDTLS_ECP_DP_SECP192R1_ENABLED
 mbedtls_ecp_curve_info:MBEDTLS_ECP_DP_SECP192R1:19:192:"secp192r1"
 
-ECP check pubkey Montgomery #1 (too big)
+ECP check pubkey Montgomery #1 (biggest)
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_check_pub:MBEDTLS_ECP_DP_CURVE25519:"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF":"0":"1":0
+
+ECP check pubkey Montgomery #2 (too big)
 depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
 ecp_check_pub:MBEDTLS_ECP_DP_CURVE25519:"010000000000000000000000000000000000000000000000000000000000000000":"0":"1":MBEDTLS_ERR_ECP_INVALID_KEY
 
-ECP check pubkey Montgomery #2 (biggest)
+ECP check pubkey Montgomery #3 (DoS big)
 depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
-ecp_check_pub:MBEDTLS_ECP_DP_CURVE25519:"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF":"0":"1":0
+ecp_check_pub:MBEDTLS_ECP_DP_CURVE25519:"0100000000000000000000000000000000000000000000000000000000000000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF":"0":"1":MBEDTLS_ERR_ECP_INVALID_KEY
 
 ECP check pubkey Montgomery y ignored
 depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED