OpenSSL Crypto Library

#include <stdio.h>
#include <openssl/hmac.h>

void dumphex(const unsigned char *src, size_t len)
{
    size_t i;
    for (i = 0; i < len; i++) {
        fprintf(stderr, "%02x", src[i]);
    }
    printf("\n");
}

int main() {
    unsigned char input[3] = {'a', 'b', 'c'};
    unsigned char key[4] = {'k', 'e', 'y', '1'};
    unsigned char hash_outbuf[EVP_MAX_MD_SIZE];
    unsigned int hash_len;
    const EVP_MD *evp_md = EVP_sha256();

    HMAC(evp_md, key, 4, input, 3, hash_outbuf, &hash_len);
    fprintf(stderr, "msg=abc, key=key1, sha256: ");
    dumphex(hash_outbuf, hash_len); // 8ca63d43eee01f745de3fc6c2b2cdf1824b6ef81b1179bc3ca650d4288d3f445
    return 0;
}

// From https://github.com/openssl/openssl/blob/master/crypto/hmac/hmac.c
unsigned char *HMAC(const EVP_MD *evp_md, const void *key, int key_len,
                    const unsigned char *d, size_t n, unsigned char *md,
                    unsigned int *md_len)
{
    HMAC_CTX *c = NULL;
    static unsigned char m[EVP_MAX_MD_SIZE];
    static const unsigned char dummy_key[1] = {'\0'};

    if (md == NULL)
        md = m;
    if ((c = HMAC_CTX_new()) == NULL)
        goto err;

    /* For HMAC_Init_ex, NULL key signals reuse. */
    if (key == NULL && key_len == 0) {
        key = dummy_key;
    }

    if (!HMAC_Init_ex(c, key, key_len, evp_md, NULL))
        goto err;
    if (!HMAC_Update(c, d, n))
        goto err;
    if (!HMAC_Final(c, md, md_len))
        goto err;
    HMAC_CTX_free(c);
    return md;
 err:
    HMAC_CTX_free(c);
    return NULL;
}

#include <stdio.h>
#include <openssl/ec.h>
#include <openssl/objects.h>

int CURVE_NAME = NID_secp256k1;

void dumpBN(const BIGNUM *bn) {
    char *buf;
    if ((buf = BN_bn2hex(bn)) == NULL) {
        return;
    }
    fprintf(stderr, "%s\n", buf);
    OPENSSL_free(buf); // must free memory allocated by BN_bn2hex
}

void dumpPoint(const EC_POINT *point) {
    EC_GROUP *group;
    char *hex;

    if ((group=EC_GROUP_new_by_curve_name(CURVE_NAME)) == NULL) {
        return;
    }
    hex = EC_POINT_point2hex(group, point, POINT_CONVERSION_UNCOMPRESSED, NULL);
    fprintf(stderr, "%s\n", hex);
    OPENSSL_free(hex); // must free memory allocated by EC_POINT_point2hex
}

int main() {
    EC_KEY *key;
    const BIGNUM *privateKey; // 私钥是一个大整数
    const EC_POINT *publicKey; // 公钥是椭圆曲线上的一个点

    // 创建 key 对象
    if (( key = EC_KEY_new_by_curve_name(CURVE_NAME)) == NULL) {
        return 1;
    }
    // 随机生成一个 key
    EC_KEY_generate_key(key);

    // 从 key 中得到私钥
    privateKey = EC_KEY_get0_private_key(key);
    dumpBN(privateKey);

    // 从 key 中得到公钥
    publicKey = EC_KEY_get0_public_key(key);
    dumpPoint(publicKey);

    return 0;
}