Loading a PEM format certificate - c++

Question

How do I load the PEM format certificate as an x509 in openssl c++?
int SSL_use_certificate(SSL *ssl, X509 *x);
int SSL_use_certificate_ASN1(SSL *ssl, unsigned char *d, int len);
int SSL_use_certificate_file(SSL *ssl, const char *file, int type);
These are the 3 functions available to add a certificate to a Handle. I have a certificate string inside the program(This is just a PEM formatted data). I want to add it to the handle. How do I proceed?
Will SSL_CTX_set_default_passwd_cb work with private keys that I am loading into and ssl handle and not a context?

Answer 1

How do I load the PEM format certificate as an x509 in openssl c++?
You should probably use SSL_CTX_use_certificate_chain_file and SSL_CTX_use_PrivateKey_file. You can use them and build a client or server context. The sample code is shown below. There are some nuances to using them, so take a look at OpenSSL's documentation at SSL_CTX_use_certificate(3).
I'm not sure what "as an x509" means. The certificate will be x509, but the private key will be PKCS #8. There are PEM_read_bio_X509 and PEM_read_X509, they return an X509*, and they may do what you want.
Will SSL_CTX_set_default_passwd_cb work with private keys that I am loading
It depends, but it should. The password callback is optional. Use it if you password protected the key. In the code below, I call it PasswordCallback, and its used for both reading and writing the key (only reading is shown below).
using SSL_CTX_ptr = std::unique_ptr<SSL_CTX, decltype(&::SSL_CTX_free)>;
SSL_CTX* CreateServerContext()
{
do
{
int rc;
unsigned long err;
const SSL_METHOD* method = SSLv23_server_method();
ASSERT(method != NULL);
if (method == NULL)
{
LogError("GetServerContext: SSLv23_server_method failed");
break; /* failed */
}
SSL_CTX_ptr t(SSL_CTX_new(method), ::SSL_CTX_free);
ASSERT(t.get() != NULL);
if (t.get() == NULL)
{
LogError("GetServerContext: SSL_CTX_new failed");
break; /* failed */
}
long flags = SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3;
flags |= SSL_OP_NO_COMPRESSION;
flags |= SSL_OP_SAFARI_ECDHE_ECDSA_BUG;
flags |= SSL_OP_CIPHER_SERVER_PREFERENCE;
/* Cannot fail */
SSL_CTX_set_options(t.get(), flags);
string ciphers = GetServerCipherSuites();
ASSERT(!ciphers.empty());
rc = SSL_CTX_set_cipher_list(t.get(), ciphers.c_str());
err = ERR_get_error();
ASSERT(rc == 1);
if (rc != 1)
{
LogError("GetServerContext: SSL_CTX_set_cipher_list failed");
break; /* failed */
}
string certFile = config.GetServerCertFile();
ASSERT(!certFile.empty());
rc = SSL_CTX_use_certificate_chain_file(t.get(), certFile.c_str());
err = ERR_get_error();
ASSERT(rc == 1);
if (rc != 1)
{
LogError("GetServerContext: SSL_CTX_use_certificate_chain_file failed");
break; /* failed */
}
/* These two do not return a value... cannot fail? */
SSL_CTX_set_default_passwd_cb(t.get(), PasswordCallback);
SSL_CTX_set_default_passwd_cb_userdata(t.get(), (void*) SERVER_KEY_LABEL);
string keyFile = config.GetServerKeyFile();
ASSERT(!keyFile.empty());
rc = SSL_CTX_use_PrivateKey_file(t.get(), keyFile.c_str(), SSL_FILETYPE_PEM);
err = ERR_get_error();
ASSERT(rc == 1);
if (rc != 1)
{
LogError("GetServerContext: SSL_CTX_use_PrivateKey_file failed");
break; /* failed */
}
rc = SSL_CTX_check_private_key(t.get());
err = ERR_get_error();
ASSERT(rc == 1);
if (rc != 1)
{
LogError("GetServerContext: SSL_CTX_check_private_key failed");
/* non-fatal, but everything will probably break */
}
/* These three do not return a value... cannot fail? */
SSL_CTX_set_tmp_dh_callback(t.get(), DhCallback);
SSL_CTX_set_tmp_ecdh_callback(t.get(), EcdhCallback);
SSL_CTX_set_tlsext_servername_callback(t.get(), ServerNameCallback);
return t.release();
} while (0);
return NULL;
}
The idea with the password callback is: OpenSSL provides you a buffer and a size. You fill the buffer, and return the size of how much you filled.
My password callback is somewhat involved. It performs a single hash of the raw password before passing it on to the library. That ensures a "plain text" password is not used (but does not slow down the customary attacks). Yours can prompt the user for a string, or it can return a hard coded string.
My password callback uses a label. The label allows me to derive different keys depending on usage (even though the same 'base' secret is used). By specifying a different usage or label, I get a different derivation of key bits. The label is provided through arg below, and you can set it with SSL_CTX_set_default_passwd_cb_userdata.
using EVP_MD_CTX_ptr = std::unique_ptr<EVP_MD_CTX, decltype(&::EVP_MD_CTX_destroy)>;
int PasswordCallback(char *buffer, int size, int rwflag, void *arg)
{
UNUSED(rwflag);
int rc;
unsigned long err;
ostringstream oss;
const char* label = (char*) arg;
size_t lsize = (label ? strlen(label) : 0);
SecureVector sv = config.GetMasterKey();
AC_ASSERT(!sv.empty());
if (sv.empty())
{
...
throw runtime_error(oss.str().c_str());
}
EVP_MD_CTX_ptr ctx(EVP_MD_CTX_create(), ::EVP_MD_CTX_destroy);
AC_ASSERT(ctx.get() != NULL);
const EVP_MD* hash = EVP_sha512();
AC_ASSERT(hash != NULL);
rc = EVP_DigestInit_ex(ctx.get(), hash, NULL);
err = ERR_get_error();
AC_ASSERT(rc == 1);
if (rc != 1)
{
...
throw runtime_error(oss.str().c_str());
}
rc = EVP_DigestUpdate(ctx.get(), sv.data(), sv.size());
err = ERR_get_error();
AC_ASSERT(rc == 1);
if (rc != 1)
{
...
throw runtime_error(oss.str().c_str());
}
if (label && lsize)
{
rc = EVP_DigestUpdate(ctx.get(), label, lsize);
err = ERR_get_error();
AC_ASSERT(rc == 1);
if (rc != 1)
{
...
throw runtime_error(oss.str().c_str());
}
}
int n = std::min(size, EVP_MD_size(hash));
if (n <= 0)
return 0;
rc = EVP_DigestFinal_ex(ctx.get(), (unsigned char*) buffer, (unsigned int*) &n);
err = ERR_get_error();
AC_ASSERT(rc == 1);
if (rc != 1)
{
...
throw runtime_error(oss.str().c_str());
}
return n;
}