EVP_PKEY-SM2(7ossl)

📦 version 3.5.0, in opensuse-leap 16.0

🌸 EVP_PKEY-SM2 💅

okay so bestie, welcome to the EVP_PKEY-SM2 glow-up — this is the 7ossl manual page, and it's literally all about the EVP_PKEY keytype support for the Chinese SM2 signature and encryption algorithms. also EVP_KEYMGMT-SM2 and plain SM2 are in the title gang, iykyk. let's get into it 🫶

✨ NAME ✨

EVP_PKEY-SM2, EVP_KEYMGMT-SM2, SM2 — EVP_PKEY keytype support for the Chinese SM2 signature and encryption algorithms. that's the whole vibe. 💖

🦋 DESCRIPTION 🦋

so the SM2 algorithm was first defined by the Chinese national standard GM/T 0003-2012, and then later got standardized by ISO as ISO/IEC 14888. and like — plot twist — SM2 is actually an elliptic curve based algorithm. no cap. the current implementation in OpenSSL supports both signature and encryption schemes via the EVP interface. slay. ✨

when you're doing the SM2 signature algorithm, it requires a distinguishing identifier to form the message prefix, and that prefix gets hashed before the real message is hashed. so it's a whole two-step hash situation, main character energy only. 🔥

🎀 Common SM2 parameters 🎀

SM2 uses the parameters defined in "Common EC parameters" in EVP_PKEY-EC(7). but the following ones are different, so pay attention bestie:

  • "cofactor" (OSSL_PKEY_PARAM_EC_COFACTOR) <unsigned integer> — this parameter is ignored for SM2. literally not invited to the party. 💀
  • (OSSL_PKEY_PARAM_DEFAULT_DIGEST) <UTF8 string> — a getter that returns the default digest name. (currently returns "SM3" as of OpenSSL 3.0). she's consistent, we love her. 💜

👑 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, except you call the 'DigestVerify' series of APIs instead. 🌈

⚠️ 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. like, mandatory mandatory. no public key, no signature. 😭

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);

and there is normally no need to pass a pctx parameter to EVP_DigestSignInit() or EVP_DigestVerifyInit() in such a scenario. so don't do extra work for no reason, bestie — we're efficient here. 💅

SM2 can be tested with the openssl-speed(1) application since version 3.0. currently, the only valid algorithm name is sm2. that's it. that's the list. one name. ⭐

since version 3.0, SM2 keys can be generated and loaded only when the domain parameters specify the SM2 elliptic curve. no substitutions, no swaps. 🧚

💖 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)

(and yes, that last line is exactly how it appears here — no trailing semicolon in the original, so we're keeping it exactly character for character. 🫶)

🌸 SEE ALSO 🌸

go read these next, bestie, they're all linked up:

Copyright 2018-2024 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>.

and that's the whole page, diva 💅 signed off sweetly — this little icon is from version 3.5.0, dated 2026-09-25. go forth and SM2 responsibly 🦋✨

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