Hello list,
I am trying to use OpenSSL to provide SSH-like trust model, by using TLS.
That means that the two peers have an RSA key pair stored, no certificate.
They have also exchanged their public keys in a secure manner. Here is the
way I do it, I would appreciate all opinions on this:
* During initialisation peers generate an in-memory, temporary x509
certificate. It contains the minimal dummy data I could get away with,
i.e. a dummy CN, issuer, and 100 years lifetime before expiring. These are
never checked anyway.
* The important step is that the certificate contains the peer's public
key and it is signed using the peer's private key:
EVP_PKEY *pkey = EVP_PKEY_new();
EVP_PKEY_assign_RSA(pkey, PRIVKEY);
X509_set_pubkey(x509, pkey);
X509_sign(x509, pkey, EVP_sha384());
* The x509 certificate is then assigned to SSL_CTX
(SSL_CTX_use_certificate()) and is used for the whole application
lifetime.
* For trust establishment I disable the callback mechanism
(SSL_CTX_set_cert_verify_callback(always_success_callback)) mainly because
I had issues with multiple threads. I also set the option to request
certificate both ways (SSL_CTX_set_verify(SSL_VERIFY_PEER) in both peers).
Immediately after each TLS session is established I do the following:
X509 *received_cert = SSL_get_peer_certificate(ssl);
EVP_PKEY *received_pubkey = X509_get_pubkey(received_cert);
// expected_rsa_key is the foreign peer's public key, we assume it has been
safely exchanged
EVP_PKEY expected_pubkey = { 0 };
ret = EVP_PKEY_assign_RSA(&expected_pubkey, expected_rsa_key);
ret = EVP_PKEY_cmp(received_pubkey, &expected_pubkey);
if (ret == 1)
return 1; // THE SESSION IS SECURE!
else
return 0; // WATCH-OUT!
That means I ignore all of the certificate besides the public key, which I
compare to the stored one. The in-memory certificate is re-generated from
the stored RSA key every time the application starts.
Do you think this is a secure design/implementation for my requirements?
Can you identify any flaws?
Thank you in advance,
Dimitris
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