source: vbox/trunk/src/libs/openssl-3.1.5/doc/man3/ECDSA_SIG_new.pod@ 104512

=pod

=head1 NAME

ECDSA_SIG_new, ECDSA_SIG_free,
ECDSA_SIG_get0, ECDSA_SIG_get0_r, ECDSA_SIG_get0_s, ECDSA_SIG_set0
- Functions for creating, destroying and manipulating ECDSA_SIG objects

=head1 SYNOPSIS

 #include <openssl/ecdsa.h>

 ECDSA_SIG *ECDSA_SIG_new(void);
 void ECDSA_SIG_free(ECDSA_SIG *sig);
 void ECDSA_SIG_get0(const ECDSA_SIG *sig, const BIGNUM **pr, const BIGNUM **ps);
 const BIGNUM *ECDSA_SIG_get0_r(const ECDSA_SIG *sig);
 const BIGNUM *ECDSA_SIG_get0_s(const ECDSA_SIG *sig);
 int ECDSA_SIG_set0(ECDSA_SIG *sig, BIGNUM *r, BIGNUM *s);

=head1 DESCRIPTION

B<ECDSA_SIG> is an opaque structure consisting of two BIGNUMs for the
I<r> and I<s> value of an Elliptic Curve Digital Signature Algorithm (ECDSA) signature
(see FIPS186-4 or X9.62).
The B<ECDSA_SIG> object was mainly used by the deprecated low level functions described in
L<ECDSA_sign(3)>, it is still required in order to be able to set or get the values of
I<r> and I<s> into or from a signature. This is mainly used for testing purposes as shown
in the L</EXAMPLES>.

ECDSA_SIG_new() allocates an empty B<ECDSA_SIG> structure.
Note: before OpenSSL 1.1.0, the I<r> and I<s> components were initialised.

ECDSA_SIG_free() frees the B<ECDSA_SIG> structure I<sig>.

ECDSA_SIG_get0() returns internal pointers the I<r> and I<s> values contained
in I<sig> and stores them in I<*pr> and I<*ps>, respectively.
The pointer I<pr> or I<ps> can be NULL, in which case the corresponding value
is not returned.

The values I<r>, I<s> can also be retrieved separately by the corresponding
function ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s(), respectively.

Non-NULL I<r> and I<s> values can be set on the I<sig> by calling
ECDSA_SIG_set0(). Calling this function transfers the memory management of the
values to the B<ECDSA_SIG> object, and therefore the values that have been
passed in should not be freed by the caller.

See L<i2d_ECDSA_SIG(3)> and L<d2i_ECDSA_SIG(3)> for information about encoding
and decoding ECDSA signatures to/from DER.

=head1 RETURN VALUES

ECDSA_SIG_new() returns NULL if the allocation fails.

ECDSA_SIG_set0() returns 1 on success or 0 on failure.

ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s() return the corresponding value,
or NULL if it is unset.

=head1 EXAMPLES

Extract signature I<r> and I<s> values from a ECDSA I<signature>
of size I<signaturelen>:

 ECDSA_SIG *obj;
 const BIGNUM *r, *s;

 /* Load a signature into the ECDSA_SIG object */
 obj = d2i_ECDSA_SIG(NULL, &signature, signaturelen);
 if (obj == NULL)
     /* error */

 r = ECDSA_SIG_get0_r(obj);
 s = ECDSA_SIG_get0_s(obj);
 if (r == NULL || s == NULL)
     /* error */

 /* Use BN_bn2binpad() here to convert to r and s into byte arrays */

 /*
  * Do not try to access I<r> or I<s> after calling ECDSA_SIG_free(),
  * as they are both freed by this call.
  */
 ECDSA_SIG_free(obj);

Convert I<r> and I<s> byte arrays into an ECDSA_SIG I<signature> of
size I<signaturelen>:

 ECDSA_SIG *obj = NULL;
 unsigned char *signature = NULL;
 size_t signaturelen;
 BIGNUM *rbn = NULL, *sbn = NULL;

 obj = ECDSA_SIG_new();
 if (obj == NULL)
     /* error */
 rbn = BN_bin2bn(r, rlen, NULL);
 sbn = BN_bin2bn(s, slen, NULL);
 if (rbn == NULL || sbn == NULL)
     /* error */

 if (!ECDSA_SIG_set0(obj, rbn, sbn))
     /* error */
 /* Set these to NULL since they are now owned by obj */
 rbn = sbn = NULL;

 signaturelen = i2d_ECDSA_SIG(obj, &signature);
 if (signaturelen <= 0)
     /* error */

 /*
  * This signature could now be passed to L<EVP_DigestVerify(3)>
  * or L<EVP_DigestVerifyFinal(3)>
  */

 BN_free(rbn);
 BN_free(sbn);
 OPENSSL_free(signature);
 ECDSA_SIG_free(obj);

=head1 CONFORMING TO

ANSI X9.62,
US Federal Information Processing Standard FIPS186-4
(Digital Signature Standard, DSS)

=head1 SEE ALSO

L<EC_KEY_new(3)>,
L<EVP_DigestSignInit(3)>,
L<EVP_DigestVerifyInit(3)>,
L<EVP_PKEY_sign(3)>
L<i2d_ECDSA_SIG(3)>,
L<d2i_ECDSA_SIG(3)>,
L<ECDSA_sign(3)>

=head1 COPYRIGHT

Copyright 2004-2022 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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