mbedtls_ecp_write_key_ext(): new function

Same as mbedtls_ecp_write_key(), but doesn't require the caller to figure out
the length of the output and possibly distinguish between Weierstrass and
Montgomery curves.

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 1dd963a..fd63657 100644
--- a/tests/suites/test_suite_ecp.data
+++ b/tests/suites/test_suite_ecp.data
@@ -888,6 +888,109 @@
 depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
 ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000080":55:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
 
+ECP write key ext: secp256r1, nominal
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":32:0
+
+ECP write key ext: secp256r1, output longer by 1
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":33:0
+
+ECP write key ext: secp256r1, output short by 1
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":31:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: secp256r1, output_size=0
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":0:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: secp256r1, top byte = 0, output_size=32
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"00ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff":32:0
+
+ECP write key ext: secp256r1, top byte = 0, output_size=31
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"00ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff":31:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: secp256r1, top byte = 0, output_size=30
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"00ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff":30:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: secp256r1, mostly-0 key, output_size=32
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"0000000000000000000000000000000000000000000000000000000000000001":32:0
+
+ECP write key ext: secp256r1, mostly-0 key, output_size=1
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"0000000000000000000000000000000000000000000000000000000000000001":1:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: secp256r1, private key not set
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP256R1:"":32:MBEDTLS_ERR_ECP_BAD_INPUT_DATA
+
+ECP write key ext: secp384r1, nominal
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":48:0
+
+ECP write key ext: secp384r1, output longer by 1
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":49:0
+
+ECP write key ext: secp384r1, output short by 1
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":47:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: Curve25519, nominal
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":32:0
+
+ECP write key ext: Curve25519, output longer by 1
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":33:0
+
+ECP write key ext: Curve25519, output short by 1
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":31:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: Curve25519, output_size=0
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":0:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: Curve25519, mostly-0 key, output_size=32
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE25519:"0000000000000000000000000000000000000000000000000000000000000040":32:0
+
+ECP write key ext: Curve25519, mostly-0 key, output_size=31
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE25519:"0000000000000000000000000000000000000000000000000000000000000040":31:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: Curve25519, private key not set
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE25519:"":32:MBEDTLS_ERR_ECP_BAD_INPUT_DATA
+
+ECP write key ext: Curve448, nominal
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":56:0
+
+ECP write key ext: Curve448, output longer by 1
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":57:0
+
+ECP write key ext: Curve448, output short by 1
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":55:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: Curve448, mostly-0 key, output_size=56
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE448:"0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000080":56:0
+
+ECP write key ext: Curve448, mostly-0 key, output_size=55
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key_ext:MBEDTLS_ECP_DP_CURVE448:"0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000080":55:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key ext: group not set
+ecp_write_key_ext:MBEDTLS_ECP_DP_NONE:"":32:MBEDTLS_ERR_ECP_BAD_INPUT_DATA
+
 ECP mod p192 small (more than 192 bits, less limbs than 2 * 192 bits)
 depends_on:MBEDTLS_ECP_DP_SECP192R1_ENABLED:MBEDTLS_ECP_NIST_OPTIM
 ecp_fast_mod:MBEDTLS_ECP_DP_SECP192R1:"0100000000000103010000000000010201000000000001010100000000000100"