Add unit tests for mbedtls_ecp_gen_privkey_mx

Test the exact output from known RNG input. This is overly
constraining, but ensures that the code has good properties.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_ecp.data b/tests/suites/test_suite_ecp.data
index 106791c..f66522a 100644
--- a/tests/suites/test_suite_ecp.data
+++ b/tests/suites/test_suite_ecp.data
@@ -276,6 +276,48 @@
 depends_on:MBEDTLS_ECP_DP_SECP192R1_ENABLED
 mbedtls_ecp_gen_key:MBEDTLS_ECP_DP_SECP192R1
 
+ECP generate Montgomery key: Curve25519, random in range
+genkey_mx_known_answer:254:"4f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1ef8":"4f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1ef8"
+
+ECP generate Montgomery key: Curve25519, set high bit
+genkey_mx_known_answer:254:"0f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1ef8":"4f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1ef8"
+
+ECP generate Montgomery key: Curve25519, clear higher bit
+## If the bit 255 is set, the library shifts the random number right.
+genkey_mx_known_answer:254:"ff0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1ef8":"7f808101820283038404850586068707880889098a0a8b0b8c0c8d0d8e0e8f78"
+
+ECP generate Montgomery key: Curve25519, clear low bits
+genkey_mx_known_answer:254:"4f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1eff":"4f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1ef8"
+
+# ECP generate Montgomery key: Curve25519, random = all-bits-zero
+## Currently explicitly rejected in the library, but the specification
+## says it shouldn't be.
+# genkey_mx_known_answer:254:"0000000000000000000000000000000000000000000000000000000000000000":"4000000000000000000000000000000000000000000000000000000000000000"
+
+ECP generate Montgomery key: Curve25519, random = all-bits-one
+genkey_mx_known_answer:254:"ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff":"7ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff8"
+
+ECP generate Montgomery key: Curve25519, not enough entropy
+genkey_mx_known_answer:254:"4f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e":""
+
+ECP generate Montgomery key: Curve448, random in range
+genkey_mx_known_answer:447:"cf0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f30313233343536fc":"cf0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f30313233343536fc"
+
+ECP generate Montgomery key: Curve448, set high bit
+genkey_mx_known_answer:447:"0f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f30313233343536fc":"8f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f30313233343536fc"
+
+ECP generate Montgomery key: Curve448, clear low bits
+genkey_mx_known_answer:447:"cf0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f30313233343536ff":"cf0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f30313233343536fc"
+
+# ECP generate Montgomery key: Curve448, random = all-bits-zero
+# genkey_mx_known_answer:447:"0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000":"8000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+
+ECP generate Montgomery key: Curve448, random = all-bits-one
+genkey_mx_known_answer:447:"ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff":"fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffc"
+
+ECP generate Montgomery key: Curve448, not enough entropy
+genkey_mx_known_answer:447:"4f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f30313233343536":""
+
 ECP read key #1 (short weierstrass, too small)
 depends_on:MBEDTLS_ECP_DP_SECP192R1_ENABLED
 mbedtls_ecp_read_key:MBEDTLS_ECP_DP_SECP192R1:"00":MBEDTLS_ERR_ECP_INVALID_KEY:0