How to convert openssl_pkey_get_public and openssl_verify to C

Question

Now I'm looking for a way to verify the signature from 'Google inapp billing' system. I've found 'openssl_pkey_get_public' and 'openssl_verify' functions in php(it is very easy and simple!!), but no example or document for C or C++;;;(I spend last two days for searching it..OTL...)

now I have :
- public key
- signature
- purchase data from google
I want to implement verifying code using C or C++

Is there someone who knows how I can get it?

I've searched belows.. - http://www.nlnetlabs.nl/downloads/publications/hsm/hsm_node21.html It deals with 'openssl EVP'..but it tells about HSM(hardware security module)

thanks!

Answer 1

below is the answer about what I've asked.. 1 means success, 0 is fail.. thanks..

int Verify_GoogleInappBilling_Signature(const char* data, const char* signature, const char* pub_key_id)
{
    std::shared_ptr<EVP_MD_CTX> mdctx = std::shared_ptr<EVP_MD_CTX>(EVP_MD_CTX_create(), EVP_MD_CTX_destroy);
    const EVP_MD* md = EVP_get_digestbyname("SHA1");
    if(NULL == md)
    {
        return -1;
    }
    if(0 == EVP_VerifyInit_ex(mdctx.get(), md, NULL))
    {
        return -1;
    }

    if(0 == EVP_VerifyUpdate(mdctx.get(), (void*)data, strlen(data)))
    {
        return -1;
    }

    std::shared_ptr<BIO> b64 = std::shared_ptr<BIO>(BIO_new(BIO_f_base64()), BIO_free);
    BIO_set_flags(b64.get(),BIO_FLAGS_BASE64_NO_NL);

    std::shared_ptr<BIO> bPubKey = std::shared_ptr<BIO>(BIO_new(BIO_s_mem()), BIO_free);
    BIO_puts(bPubKey.get(),pub_key_id);
    BIO_push(b64.get(), bPubKey.get());

    std::shared_ptr<EVP_PKEY> pubkey = std::shared_ptr<EVP_PKEY>(d2i_PUBKEY_bio(b64.get(), NULL), EVP_PKEY_free);

    std::string decoded_signature = Base64Decode(std::string(signature));
    return EVP_VerifyFinal(mdctx.get(), (unsigned char*)decoded_signature.c_str(), decoded_signature.length(), pubkey.get());
}