EVP_PKEY-SM2¶

NAME¶

EVP_PKEY-SM2, EVP_KEYMGMT-SM2, SM2 - EVP_PKEY keytype support for the Chinese SM2 signature and encryption algorithms

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).

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, 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)) or -sigopt (openssl-dgst(1)) option with a value of distid:.

Common SM2 parameters¶

SM2 uses the parameters defined in "Common EC parameters" in 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¶

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) 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¶

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... */
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)

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¶

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.