=pod

=head1 NAME

SM2 - Chinese SM2 signature and encryption algorithm support

=head1 DESCRIPTION

The B<SM2> algorithm was first defined by the Chinese national standard GM/T
0003-2012 and was later standardized by ISO as ISO/IEC 14888. B<SM2> is actually
an elliptic curve based algorithm. The current implementation in OpenSSL supports
both signature and encryption schemes via the EVP interface.

When doing the B<SM2> signature algorithm, it requires a distinguishing identifier
to form the message prefix which is hashed before the real message is hashed.

=head1 NOTES

B<SM2> signatures can be generated by using the 'DigestSign' series of APIs, for
instance, EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal().
Ditto for the verification process by calling the 'DigestVerify' series of APIs.

There are several special steps that need to be done before computing an B<SM2>
signature.

The B<EVP_PKEY> structure will default to using ECDSA for signatures when it is
created. It should be set to B<EVP_PKEY_SM2> by calling:

 EVP_PKEY_set_alias_type(pkey, EVP_PKEY_SM2);

Then an ID should be set by calling:

 EVP_PKEY_CTX_set1_id(pctx, id, id_len);

When calling the EVP_DigestSignInit() or EVP_DigestVerifyInit() functions, a
pre-allocated B<EVP_PKEY_CTX> should be assigned to the B<EVP_MD_CTX>. This is
done by calling:

 EVP_MD_CTX_set_pkey_ctx(mctx, pctx);

And normally there is no need to pass a B<pctx> parameter to EVP_DigestSignInit()
or EVP_DigestVerifyInit() in such a scenario.

=head1 EXAMPLE

This example demonstrates the calling sequence for using an B<EVP_PKEY> to verify
a message with the SM2 signature algorithm and the SM3 hash algorithm:

 #include <openssl/evp.h>

 /* obtain an EVP_PKEY using whatever methods... */
 EVP_PKEY_set_alias_type(pkey, EVP_PKEY_SM2);
 mctx = EVP_MD_CTX_new();
 pctx = EVP_PKEY_CTX_new(pkey, NULL);
 EVP_PKEY_CTX_set1_id(pctx, id, id_len);
 EVP_MD_CTX_set_pkey_ctx(mctx, pctx);;
 EVP_DigestVerifyInit(mctx, NULL, EVP_sm3(), NULL, pkey);
 EVP_DigestVerifyUpdate(mctx, msg, msg_len);
 EVP_DigestVerifyFinal(mctx, sig, sig_len)

=head1 SEE ALSO

L<EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_set_alias_type(3)>,
L<EVP_DigestSignInit(3)>,
L<EVP_DigestVerifyInit(3)>,
L<EVP_PKEY_CTX_set1_id(3)>,
L<EVP_MD_CTX_set_pkey_ctx(3)>

=head1 COPYRIGHT

Copyright 2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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>.

=cut
