Fix EC_KEY_set_private_key() NULL priv_key docs

Updates the docs to describe EC_KEY_set_private_key() function behavior
when a NULL priv_key argument is passed.

Reviewed-by: Nicola Tuveri <nic.tuv@gmail.com>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from https://github.com/openssl/openssl/pull/18942)

1 files changed, 12 insertions, 6 deletions

diff --git a/doc/man3/EC_KEY_new.pod b/doc/man3/EC_KEY_new.pod
index ce5f5e491f..98c9adc8ae 100644
--- a/doc/man3/EC_KEY_new.pod
+++ b/doc/man3/EC_KEY_new.pod
@@ -43,7 +43,7 @@ see L<openssl_user_macros(7)>:
  const EC_GROUP *EC_KEY_get0_group(const EC_KEY *key);
  int EC_KEY_set_group(EC_KEY *key, const EC_GROUP *group);
  const BIGNUM *EC_KEY_get0_private_key(const EC_KEY *key);
- int EC_KEY_set_private_key(EC_KEY *key, const BIGNUM *prv);
+ int EC_KEY_set_private_key(EC_KEY *key, const BIGNUM *priv_key);
  const EC_POINT *EC_KEY_get0_public_key(const EC_KEY *key);
  int EC_KEY_set_public_key(EC_KEY *key, const EC_POINT *pub);
  point_conversion_form_t EC_KEY_get_conv_form(const EC_KEY *key);
@@ -136,7 +136,9 @@ that it is valid.
 The functions EC_KEY_get0_group(), EC_KEY_set_group(),
 EC_KEY_get0_private_key(), EC_KEY_set_private_key(), EC_KEY_get0_public_key(),
 and EC_KEY_set_public_key() get and set the EC_GROUP object, the private key,
-and the EC_POINT public key for the I<key> respectively.
+and the EC_POINT public key for the B<key> respectively. The function
+EC_KEY_set_private_key() accepts NULL as the priv_key argument to securely clear
+the private key component from the EC_KEY.
 
 The functions EC_KEY_get_conv_form() and EC_KEY_set_conv_form() get and set the
 point_conversion_form for the I<key>. For a description of
@@ -197,10 +199,14 @@ EC_KEY_copy() returns a pointer to the destination key, or NULL on error.
 
 EC_KEY_get0_engine() returns a pointer to an ENGINE, or NULL if it wasn't set.
 
-EC_KEY_up_ref(), EC_KEY_set_group(), EC_KEY_set_private_key(),
-EC_KEY_set_public_key(), EC_KEY_precompute_mult(), EC_KEY_generate_key(),
-EC_KEY_check_key(), EC_KEY_set_public_key_affine_coordinates(),
-EC_KEY_oct2key() and EC_KEY_oct2priv() return 1 on success or 0 on error.
+EC_KEY_up_ref(), EC_KEY_set_group(), EC_KEY_set_public_key(),
+EC_KEY_precompute_mult(), EC_KEY_generate_key(), EC_KEY_check_key(),
+EC_KEY_set_public_key_affine_coordinates(), EC_KEY_oct2key() and
+EC_KEY_oct2priv() return 1 on success or 0 on error.
+
+EC_KEY_set_private_key() returns 1 on success or 0 on error except when the
+priv_key argument is NULL, in that case it returns 0, for legacy compatibility,
+and should not be treated as an error.
 
 EC_KEY_get0_group() returns the EC_GROUP associated with the EC_KEY.