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/library/ecp.c b/library/ecp.c
index 66b3dc1..930102f 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -3333,6 +3333,38 @@
return ret;
}
+int mbedtls_ecp_write_key_ext(mbedtls_ecp_keypair *key,
+ size_t *olen, unsigned char *buf, size_t buflen)
+{
+ size_t len = (key->grp.nbits + 7) / 8;
+ if (len > buflen) {
+ /* For robustness, ensure *olen <= buflen even on error. */
+ *olen = 0;
+ return MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
+ }
+ *olen = len;
+
+ /* Private key not set */
+ if (key->d.n == 0) {
+ return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
+ }
+
+#if defined(MBEDTLS_ECP_MONTGOMERY_ENABLED)
+ if (mbedtls_ecp_get_type(&key->grp) == MBEDTLS_ECP_TYPE_MONTGOMERY) {
+ return mbedtls_mpi_write_binary_le(&key->d, buf, len);
+ }
+#endif
+
+#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
+ if (mbedtls_ecp_get_type(&key->grp) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS) {
+ return mbedtls_mpi_write_binary(&key->d, buf, len);
+ }
+#endif
+
+ /* Private key set but no recognized curve type? This shouldn't happen. */
+ return MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+}
+
/*
* Write a public key.
*/