openssl C++ ecdsa 签名和验签

ECDSA（Elliptic Curve Digital Signature Algorithm）是一种基于椭圆曲线密码学的数字签名算法。OpenSSL库提供了ECDSA签名和验签的函数。

ECDSA签名：

1. 生成ECDSA密钥对：

EC_KEY *key = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
EC_KEY_generate_key(key);

2. 计算消息的哈希值：

unsigned char *msg = "Hello World";
unsigned char digest[SHA256_DIGEST_LENGTH];
SHA256(msg, strlen(msg), digest);

3. 对消息哈希值进行签名：

unsigned char *signature;
unsigned int signature_len;
signature = (unsigned char *)malloc(ECDSA_size(key));
ECDSA_sign(0, digest, SHA256_DIGEST_LENGTH, signature, &signature_len, key);

4. 将签名结果进行编码：

unsigned char *encoded_signature;
unsigned int encoded_signature_len;
encoded_signature = (unsigned char *)malloc(signature_len * 2 + 1);
ECDSA_signature_encode(ECDSA_SIG_new(), signature, signature_len, encoded_signature, &encoded_signature_len);

ECDSA验签：

1. 解码签名结果：

ECDSA_SIG *ecdsa_sig = ECDSA_SIG_new();
unsigned char *encoded_signature = "304402202a24c7d48f6a..."; // 签名结果
unsigned int encoded_signature_len = strlen(encoded_signature);
ECDSA_signature_decode(ecdsa_sig, encoded_signature, encoded_signature_len);

2. 计算消息的哈希值：

unsigned char *msg = "Hello World";
unsigned char digest[SHA256_DIGEST_LENGTH];
SHA256(msg, strlen(msg), digest);

3. 进行验签：

int result = ECDSA_do_verify(digest, SHA256_DIGEST_LENGTH, ecdsa_sig, key);
if (result == 1) {
    printf("Signature verified successfully.\n");
} else if (result == 0) {
    printf("Signature verification failed.\n");
} else {
    printf("Error occurred during signature verification.\n");
}

完整的示例代码：

#include <openssl/ec.h>
#include <openssl/ecdsa.h>
#include <openssl/obj_mac.h>
#include <openssl/sha.h>

int main() {
    EC_KEY *key = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1); // 选择椭圆曲线
    EC_KEY_generate_key(key); // 生成密钥对

    // 签名
    unsigned char *msg = "Hello World";
    unsigned char digest[SHA256_DIGEST_LENGTH];
    SHA256(msg, strlen(msg), digest); // 计算哈希值

    unsigned char *signature;
    unsigned int signature_len;
    signature = (unsigned char *)malloc(ECDSA_size(key));
    ECDSA_sign(0, digest, SHA256_DIGEST_LENGTH, signature, &signature_len, key); // 进行签名

    unsigned char *encoded_signature;
    unsigned int encoded_signature_len;
    encoded_signature = (unsigned char *)malloc(signature_len * 2 + 1);
    ECDSA_signature_encode(ECDSA_SIG_new(), signature, signature_len, encoded_signature, &encoded_signature_len); // 编码签名结果

    // 验签
    ECDSA_SIG *ecdsa_sig = ECDSA_SIG_new();
    ECDSA_signature_decode(ecdsa_sig, encoded_signature, encoded_signature_len); // 解码签名结果

    int result = ECDSA_do_verify(digest, SHA256_DIGEST_LENGTH, ecdsa_sig, key); // 进行验签
    if (result == 1) {
        printf("Signature verified successfully.\n");
    } else if (result == 0) {
        printf("Signature verification failed.\n");
    } else {
        printf("Error occurred during signature verification.\n");
    }

    ECDSA_SIG_free(ecdsa_sig);
    EC_KEY_free(key);
    free(signature);
    free(encoded_signature);

    return 0;
}