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#include <openssl/evp.h>
#include <openssl/rsa.h>
#include <iomanip>
#include <iostream>
#include <vector>
int main() {
auto ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_RSA, nullptr);
EVP_PKEY *pkey = NULL;
EVP_PKEY_keygen_init(ctx);
EVP_PKEY_CTX_set_rsa_keygen_bits(ctx, 2048);
EVP_PKEY_keygen(ctx, &pkey);
EVP_PKEY_CTX_free(ctx);
ctx = nullptr;
unsigned char cleartext[] = "abc";
int cleartext_size = sizeof(cleartext) / sizeof(cleartext[0]);
EVP_MD_CTX *md_ctx = EVP_MD_CTX_create();
EVP_DigestInit_ex(md_ctx, EVP_sha256(), NULL);
EVP_DigestUpdate(md_ctx, cleartext, cleartext_size);
unsigned char digest[EVP_MAX_MD_SIZE];
unsigned int digest_size;
EVP_DigestFinal_ex(md_ctx, digest, &digest_size);
EVP_MD_CTX_destroy(md_ctx);
md_ctx = nullptr;
std::cout << "SHA256 digest of 'abc' is: " << std::hex << std::setfill('0');
for (unsigned int i = 0; i < digest_size; i++) {
std::cout << std::setw(2) << (int)digest[i];
}
std::cout << std::endl;
std::vector<unsigned char> sig;
size_t sig_len;
ctx = EVP_PKEY_CTX_new(pkey, nullptr);
EVP_PKEY_sign_init(ctx);
EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING);
EVP_PKEY_sign(ctx, nullptr, &sig_len, digest, digest_size);
sig.resize(sig_len);
EVP_PKEY_sign(ctx, sig.data(), &sig_len, digest, digest_size);
EVP_PKEY_CTX_free(ctx);
std::cout << "Signature: " << std::hex << std::setfill('0');
for (auto c : sig) {
std::cout << std::setw(2) << static_cast<int>(c);
}
std::cout << std::endl;
ctx = EVP_PKEY_CTX_new(pkey, nullptr);
EVP_PKEY_verify_init(ctx);
EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING);
auto result = EVP_PKEY_verify(ctx, sig.data(), sig_len, digest, digest_size);
if (result == 1) {
std::cout << "Verification succeeded." << std::endl;
} else if (result == 0) {
std::cout << "Verification failed." << std::endl;
} else {
std::cerr << "Verification error." << std::endl;
}
return 0;
}
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