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=head1 NAME

i2d_ECPrivateKey, d2i_ECPrivate_key - Encode and decode functions for saving and
reading EC_KEY structures

=head1 SYNOPSIS

 #include <openssl/ec.h>

 EC_KEY *d2i_ECPrivateKey(EC_KEY **key, const unsigned char **in, long len);
 int i2d_ECPrivateKey(EC_KEY *key, unsigned char **out);

 unsigned int EC_KEY_get_enc_flags(const EC_KEY *key);
 void EC_KEY_set_enc_flags(EC_KEY *eckey, unsigned int flags);

=head1 DESCRIPTION

The ECPrivateKey encode and decode routines encode and parse an
B<EC_KEY> structure into a binary format (ASN.1 DER) and back again.

These functions are similar to the d2i_X509() functions, and you should refer to
that page for a detailed description (see L<d2i_X509(3)|d2i_X509(3)>).

The format of the external representation of the public key written by
i2d_ECPrivateKey (such as whether it is stored in a compressed form or not) is
described by the point_conversion_form. See L<EC_GROUP_copy(3)|EC_GROUP_copy(3)>
for a description of point_conversion_form.

When reading a private key encoded without an associated public key (e.g. if
EC_PKEY_NO_PUBKEY has been used - see below), then d2i_ECPrivateKey generates
the missing public key automatically. Private keys encoded without parameters
(e.g. if EC_PKEY_NO_PARAMETERS has been used - see below) cannot be loaded using
d2i_ECPrivateKey.

The functions EC_KEY_get_enc_flags and EC_KEY_set_enc_flags get and set the
value of the encoding flags for the B<key>. There are two encoding flags
currently defined - EC_PKEY_NO_PARAMETERS and EC_PKEY_NO_PUBKEY.  These flags
define the behaviour of how the  B<key> is converted into ASN1 in a call to
i2d_ECPrivateKey. If EC_PKEY_NO_PARAMETERS is set then the public parameters for
the curve are not encoded along with the private key. If EC_PKEY_NO_PUBKEY is
set then the public key is not encoded along with the private key.

=head1 RETURN VALUES

d2i_ECPrivateKey() returns a valid B<EC_KEY> structure or B<NULL> if an error
occurs. The error code that can be obtained by
L<ERR_get_error(3)|ERR_get_error(3)>.

i2d_ECPrivateKey() returns the number of bytes successfully encoded or a
negative value if an error occurs. The error code can be obtained by
L<ERR_get_error(3)|ERR_get_error(3)>.

EC_KEY_get_enc_flags returns the value of the current encoding flags for the
EC_KEY.

=head1 SEE ALSO

L<crypto(3)|crypto(3)>, L<ec(3)|ec(3)>, L<EC_GROUP_new(3)|EC_GROUP_new(3)>,
L<EC_GROUP_copy(3)|EC_GROUP_copy(3)>, L<EC_POINT_new(3)|EC_POINT_new(3)>,
L<EC_POINT_add(3)|EC_POINT_add(3)>,
L<EC_GFp_simple_method(3)|EC_GFp_simple_method(3)>,
L<d2i_ECPKParameters(3)|d2i_ECPKParameters(3)>,
L<d2i_ECPrivateKey(3)|d2i_ECPrivateKey(3)>

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