New function mbedtls_ecp_write_public_key
Directly export the public part of a key pair without having to go through
intermediate objects (using mbedtls_ecp_point_write_binary would require a
group object and a point object).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index fc0a763..619a8a5 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -1347,6 +1347,32 @@
unsigned char *buf, size_t buflen);
/**
+ * \brief This function exports an elliptic curve public key.
+ *
+ * \param key The public key.
+ * \param format The point format. This must be either
+ * #MBEDTLS_ECP_PF_COMPRESSED or #MBEDTLS_ECP_PF_UNCOMPRESSED.
+ * (For groups without these formats, this parameter is
+ * ignored. But it still has to be either of the above
+ * values.)
+ * \param olen The address at which to store the length of
+ * the output in Bytes. This must not be \c NULL.
+ * \param buf The output buffer. This must be a writable buffer
+ * of length \p buflen Bytes.
+ * \param buflen The length of the output buffer \p buf in Bytes.
+ *
+ * \return \c 0 on success.
+ * \return #MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL if the output buffer
+ * is too small to hold the point.
+ * \return #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the point format
+ * or the export for the given group is not implemented.
+ * \return Another negative error code on other kinds of failure.
+ */
+int mbedtls_ecp_write_public_key(mbedtls_ecp_keypair *key,
+ int format, size_t *olen,
+ unsigned char *buf, size_t buflen);
+
+/**
* \brief This function checks that the keypair objects
* \p pub and \p prv have the same group and the
* same public point, and that the private key in