Compute SM2 encryption and decryption by invoking EVP interface in OpenSSL 1.1.1

    How to compute SM2 signature and verify it is introduced in the previous article. In this post a demo of performing SM2 encryption and decryption by invoking EVP interface in OpenSSL 1.1.1 is provided:

/**************************************************
* File name: EVP_sm2_encrypt_and_decrypt.c
* Author: HAN Wei
* Author's blog: https://blog.csdn.net/henter/
* Date: May 1st, 2020
* Description: demonstrate how to compute SM2 encryption
	   and decryption by invoking EVP interface
	   in OpenSSL 1.1.1
**************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "openssl/ec.h"
#include "openssl/evp.h"

/**************************************************
* Main function return value:
	0:   main function executes successfully
	-1:  an error occurs
**************************************************/
int main(void)
{
	int ret = -1, i;
	EVP_PKEY_CTX *pctx = NULL, *ectx = NULL;
	EVP_PKEY *pkey = NULL;
	unsigned char message[16] = { 0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7,
				  0x8, 0x9, 0xA, 0xB, 0xC, 0xD, 0xE, 0xF };
	size_t message_len = sizeof(message);
	unsigned char *ciphertext = NULL, *plaintext = NULL;
	size_t ciphertext_len, plaintext_len;
	EC_KEY *key_pair = NULL;
	const BIGNUM *priv_key = NULL;
	char *priv_key_str = NULL;

	const EC_GROUP *group = NULL;
	const EC_POINT *pub_key = NULL;
	BN_CTX *ctx = NULL;
	BIGNUM *x_coordinate = NULL, *y_coordinate = NULL;
	char *x_coordinate_str = NULL, *y_coordinate_str = NULL;

/* create SM2 Ellipse Curve parameters and key pair */
	if ( !(pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_EC, NULL)) )
	{
		goto clean_up;
	}

	if ( (EVP_PKEY_paramgen_init(pctx)) != 1 )
	{
		goto clean_up;
	}

	if ( (EVP_PKEY_CTX_set_ec_paramgen_curve_nid(pctx, NID_sm2)) <= 0 )
	{
		goto clean_up;
	}

	if ( (EVP_PKEY_******_init(pctx)) != 1 )
	{
		goto clean_up;
	}

	if ( (EVP_PKEY_******(pctx, &pkey)) != 1 )
	{
		goto clean_up;
	}

/* print SM2 key pair */
	if ( !(key_pair = EVP_PKEY_get0_EC_KEY(pkey)) )
	{
		goto clean_up;
	}

	if ( !(priv_key = EC_KEY_get0_private_key(key_pair)) )
	{
		goto clean_up;
	}

	if ( !(priv_key_str = BN_bn2hex(priv_key)) )
	{
		goto clean_up;
	}
	printf("SM2 private key (in hex form):\n");
	printf("%s\n\n", priv_key_str);

	if ( !(pub_key = EC_KEY_get0_public_key(key_pair)) )
	{
		goto clean_up;
	}

	if ( !(group = EC_KEY_get0_group(key_pair)) )
	{
		goto clean_up;
	}

	if ( !(ctx = BN_CTX_new()) )
	{
		goto clean_up;
	}
	BN_CTX_start(ctx);
	x_coordinate = BN_CTX_get(ctx);
	y_coordinate = BN_CTX_get(ctx);
	if ( !(y_coordinate) )
	{
		goto clean_up;
	}
	if ( !(EC_POINT_get_affine_coordinates(group, pub_key, x_coordinate, y_coordinate, ctx)) )
	{
		goto clean_up;
	}
	if ( !(x_coordinate_str = BN_bn2hex(x_coordinate)) )
	{
		goto clean_up;
	}
	printf("x coordinate in SM2 public key (in hex form):\n");
	printf("%s\n\n", x_coordinate_str);

	if ( !(y_coordinate_str = BN_bn2hex(y_coordinate)) )
	{
		goto clean_up;
	}
	printf("y coordinate in SM2 public key (in hex form):\n");
	printf("%s\n\n", y_coordinate_str);

/* compute SM2 encryption */
	if ( (EVP_PKEY_set_alias_type(pkey, EVP_PKEY_SM2)) != 1 )
	{
		goto clean_up;
	}

	if ( !(ectx = EVP_PKEY_CTX_new(pkey, NULL)) )
	{
		goto clean_up;
	}

	if ( (EVP_PKEY_encrypt_init(ectx)) != 1 )
	{
		goto clean_up;
	}

	if ( (EVP_PKEY_encrypt(ectx, NULL, &ciphertext_len, message, message_len)) != 1 )
	{
		goto clean_up;
	}

	if ( !(ciphertext = (unsigned char *)malloc(ciphertext_len)) )
	{
		goto clean_up;
	}

	if ( (EVP_PKEY_encrypt(ectx, ciphertext, &ciphertext_len, message, message_len)) != 1 )
	{
		goto clean_up;
	}

	printf("Message length: %d bytes.\n", message_len);
	printf("Message:\n");
	for (i = 0; i < (int)message_len; i++)
	{
		printf("0x%x  ", message[i]);
	}
	printf("\n\n");

	printf("Ciphertext length: %d bytes.\n", ciphertext_len);
	printf("Ciphertext (ASN.1 encode):\n");
	for (i = 0; i < (int)ciphertext_len; i++)
	{
		printf("0x%x  ", ciphertext[i]);
	}
	printf("\n\n");

/* compute SM2 decryption */
	if ( (EVP_PKEY_decrypt_init(ectx)) != 1 )
	{
		goto clean_up;
	}

	if ( (EVP_PKEY_decrypt(ectx, NULL, &plaintext_len, ciphertext, ciphertext_len)) != 1 )
	{
		goto clean_up;
	}

	if ( !(plaintext = (unsigned char *)malloc(plaintext_len)) )
	{
		goto clean_up;
	}

	if ( (EVP_PKEY_decrypt(ectx, plaintext, &plaintext_len, ciphertext, ciphertext_len)) != 1 )
	{
		goto clean_up;
	}

	printf("Decrypted plaintext length: %d bytes.\n", plaintext_len);
	printf("Decrypted plaintext:\n");
	for (i = 0; i < (int)plaintext_len; i++)
	{
		printf("0x%x  ", plaintext[i]);
	}
	printf("\n\n");

	if ( plaintext_len != message_len )
	{
		printf("Decrypted data length error!\n");
		goto clean_up;
	}

	if ( memcmp(plaintext, message, message_len) )
	{
		printf("Decrypt data failed!\n");
		goto clean_up;
	}
	else
	{
		printf("Encrypt and decrypt data succeeded!\n");
	}

	ret = 0;
clean_up:
	if (pctx)
	{
		EVP_PKEY_CTX_free(pctx);
	}

	if (pkey)
	{
		EVP_PKEY_free(pkey);
	}

	if (priv_key_str)
	{
		OPENSSL_free(priv_key_str);
	}

	if (ctx)
	{
		BN_CTX_end(ctx);
		BN_CTX_free(ctx);
	}

	if (x_coordinate_str)
	{
		OPENSSL_free(x_coordinate_str);
	}

	if (y_coordinate_str)
	{
		OPENSSL_free(y_coordinate_str);
	}

	if (ectx)
	{
		EVP_PKEY_CTX_free(ectx);
	}

	if (ciphertext)
	{
		free(ciphertext);
	}

	if (plaintext)
	{
		free(plaintext);
	}

#if defined(_WIN32) || defined(_WIN64)
	system("pause");
#endif
	return ret;
}

    The result is as below: