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.\" ========================================================================
.\"
.IX Title "SM2 7"
.TH SM2 7 "2023-09-11" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
SM2 \- Chinese SM2 signature and encryption algorithm support
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fB\s-1SM2\s0\fR algorithm was first defined by the Chinese national standard \s-1GM/T
0003\-2012\s0 and was later standardized by \s-1ISO\s0 as \s-1ISO/IEC 14888. \s0\fB\s-1SM2\s0\fR is actually
an elliptic curve based algorithm. The current implementation in OpenSSL supports
both signature and encryption schemes via the \s-1EVP\s0 interface.
.PP
When doing the \fB\s-1SM2\s0\fR signature algorithm, it requires a distinguishing identifier
to form the message prefix which is hashed before the real message is hashed.
.SH "NOTES"
.IX Header "NOTES"
\&\fB\s-1SM2\s0\fR signatures can be generated by using the 'DigestSign' series of APIs, for
instance, \fIEVP_DigestSignInit()\fR, \fIEVP_DigestSignUpdate()\fR and \fIEVP_DigestSignFinal()\fR.
Ditto for the verification process by calling the 'DigestVerify' series of APIs.
.PP
There are several special steps that need to be done before computing an \fB\s-1SM2\s0\fR
signature.
.PP
The \fB\s-1EVP_PKEY\s0\fR structure will default to using \s-1ECDSA\s0 for signatures when it is
created. It should be set to \fB\s-1EVP_PKEY_SM2\s0\fR by calling:
.PP
.Vb 1
\& EVP_PKEY_set_alias_type(pkey, EVP_PKEY_SM2);
.Ve
.PP
Then an \s-1ID\s0 should be set by calling:
.PP
.Vb 1
\& EVP_PKEY_CTX_set1_id(pctx, id, id_len);
.Ve
.PP
When calling the \fIEVP_DigestSignInit()\fR or \fIEVP_DigestVerifyInit()\fR functions, a
preallocated \fB\s-1EVP_PKEY_CTX\s0\fR should be assigned to the \fB\s-1EVP_MD_CTX\s0\fR. This is
done by calling:
.PP
.Vb 1
\& EVP_MD_CTX_set_pkey_ctx(mctx, pctx);
.Ve
.PP
And normally there is no need to pass a \fBpctx\fR parameter to \fIEVP_DigestSignInit()\fR
or \fIEVP_DigestVerifyInit()\fR in such a scenario.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
This example demonstrates the calling sequence for using an \fB\s-1EVP_PKEY\s0\fR to verify
a message with the \s-1SM2\s0 signature algorithm and the \s-1SM3\s0 hash algorithm:
.PP
.Vb 1
\& #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)
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIEVP_PKEY_CTX_new\fR\|(3),
\&\fIEVP_PKEY_set_alias_type\fR\|(3),
\&\fIEVP_DigestSignInit\fR\|(3),
\&\fIEVP_DigestVerifyInit\fR\|(3),
\&\fIEVP_PKEY_CTX_set1_id\fR\|(3),
\&\fIEVP_MD_CTX_set_pkey_ctx\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2018\-2020 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.