EVP\_PKEY-SM2(7ossl) OpenSSL EVP\_PKEY-SM2(7ossl) # [NAME](#NAME) EVP\_PKEY-SM2, EVP\_KEYMGMT-SM2, SM2 - EVP\_PKEY keytype support for the Chinese SM2 signature and encryption algorithms # [DESCRIPTION](#DESCRIPTION) 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 an elliptic curve-based algorithm. Its implementation in OpenSSL supports both signature and encryption schemes via the EVP interface. Under the name "curveSM2" it also supports "ECDH over SM2" as described in [**EVP\_KEYEXCH-ECDH**(7)](/man/os/openssl-4.0/EVP_KEYEXCH-ECDH.7). The **SM2** signature algorithm takes an optional *distinguishing identifier* parameter (**OSSL\_PKEY\_PARAM\_DIST\_ID**), which is used as part of a message prefix before hashing with **SM3**. As specified in RFC 8998 <https://www.rfc-editor.org/rfc/rfc8998.html>, when **SM2** is used as part of the **sm2sig\_sm3** TLS signature scheme, this identifier must be set to the constant string "TLSv1.3+GM+Cipher+Suite". The OpenSSL TLS stack passes a protocol version parameter (**OSSL\_SIGNATURE\_PARAM\_TLS\_VERSION**) to the signature algorithm, which then in the case of **SM2** internally sets the distinguishing identifier to the expected constant. When **SM2** is used for other purposes (e.g. in certificate signing or verification), and no explicit value of the distinguishing identifier is specified, a default value of 1234567812345678 is used. An explicit empty distinguishing identifier value may need to be used to verify or create signatures that are compatible with versions of OpenSSL prior to 4.0. With the commandline tools an empty value can be specified with the use of either the **-pkeyopt** ([**openssl-pkeyutl**(1)](/man/os/openssl-4.0/openssl-pkeyutl.1)) or **-sigopt** ([**openssl-dgst**(1)](/man/os/openssl-4.0/openssl-dgst.1)) option with a value of "distid:". ## [Common SM2 parameters](#Common_SM2_parameters) SM2 uses the parameters defined in "Common EC parameters" in [**EVP\_PKEY-EC**(7)](/man/os/openssl-4.0/EVP_PKEY-EC.7). The following parameters are different: "cofactor" (**OSSL\_PKEY\_PARAM\_EC\_COFACTOR**) <unsigned integer> This parameter is ignored for **SM2**. (**OSSL\_PKEY\_PARAM\_DEFAULT\_DIGEST**) <UTF8 string> Getter that returns the default digest name. (Currently returns "SM3" as of OpenSSL 3.0). # [NOTES](#NOTES) **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. Note that the SM2 algorithm requires the presence of the public key for signatures, as such the **OSSL\_PKEY\_PARAM\_PUB\_KEY** option must be set on any key used in signature generation. Before computing an **SM2** signature, an **EVP\_PKEY\_CTX** needs to be created, and an **SM2** ID must be set for it, like this: ``` EVP_PKEY_CTX_set1_id(pctx, id, id_len); ``` Before calling the **EVP\_DigestSignInit()** or **EVP\_DigestVerifyInit()** functions, that **EVP\_PKEY\_CTX** should be assigned to the **EVP\_MD\_CTX**, like this: ``` EVP_MD_CTX_set_pkey_ctx(mctx, pctx); ``` There is normally no need to pass a **pctx** parameter to **EVP\_DigestSignInit()** or **EVP\_DigestVerifyInit()** in such a scenario. SM2 can be tested with the [**openssl-speed**(1)](/man/os/openssl-4.0/openssl-speed.1) application since version 3.0. Currently, the only valid algorithm name is **sm2**. Since version 3.0, SM2 keys can be generated and loaded only when the domain parameters specify the SM2 elliptic curve. # [EXAMPLES](#EXAMPLES) 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 /* obtain an EVP_PKEY using whatever methods... */ 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) ``` # [SEE ALSO](#SEE_ALSO) [**EVP\_PKEY\_CTX\_new**(3)](/man/os/openssl-4.0/EVP_PKEY_CTX_new.3), [**EVP\_DigestSignInit**(3)](/man/os/openssl-4.0/EVP_DigestSignInit.3), [**EVP\_DigestVerifyInit**(3)](/man/os/openssl-4.0/EVP_DigestVerifyInit.3), [**EVP\_PKEY\_CTX\_set1\_id**(3)](/man/os/openssl-4.0/EVP_PKEY_CTX_set1_id.3), [**EVP\_MD\_CTX\_set\_pkey\_ctx**(3)](/man/os/openssl-4.0/EVP_MD_CTX_set_pkey_ctx.3) # [HISTORY](#HISTORY) Support for the **sm2sig\_sm3** TLS signature scheme was added in OpenSSL 4.0. The default value of the SM2 distinguishing identifier changed from empty to 1234567812345678 as of OpenSSL 4.0. # [COPYRIGHT](#COPYRIGHT) Copyright 2018-2026 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 <https://www.openssl.org/source/license.html>. 2026-09-29 4.0.3 --- Document: SM2(7ossl) from openssl-4.0 4.0.3-r6 (Chainguard OS)