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SM2 - Chinese SM2 signature and encryption algorithm support


The SM2 algorithm was first defined by the Chinese national standard GM/T 0003-2012 and was later standardized by ISO as ISO/IEC 14888. 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 SM2 signature algorithm, it requires a distinguishing identifier to form the message prefix which is hashed before the real message is hashed.


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 SM2 signature.

The EVP_PKEY structure will default to using ECDSA for signatures when it is created. It should be set to 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 preallocated EVP_PKEY_CTX should be assigned to the 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 pctx parameter to EVP_DigestSignInit() or EVP_DigestVerifyInit() in such a scenario.


This example demonstrates the calling sequence for using an 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)


EVP_PKEY_CTX_new(3), EVP_PKEY_set_alias_type(3), EVP_DigestSignInit(3), EVP_DigestVerifyInit(3), EVP_PKEY_CTX_set1_id(3), EVP_MD_CTX_set_pkey_ctx(3)


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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 <>.

2022-05-06 1.1.1o