Is there any way that I can create a proof of a file downloaded using https? With proof I mean a cryptographic record of some sort that links the contents of a file to a site at a certain time. If I understand TLS correctly, the server certificate is only used as a basis to establish a session key that is known to both parties, so each request is not signed but just encrypted for transfer. Any ideas if this can be done and if so how?
In HTTPS the certificate is only used for authentication and with the obsolete RSA key exchange also for key exchange. Application data are only protected against modification by some man in the middle but they are not signed by the sender. While a HTTP server could be explicitly implemented to sign and timestamp the content, one can not enforce such operation against an arbitrary existing server.
For more see
Where in a TLS connection can I get the signature of the content sent by the server?
Why does HTTPS not support non-repudiation?
How to prove some server sent some file over HTTPS
Proving authenticity of data accessed over TLS by an untrusted third party
Related
For the purposes of secrecy and authenticity of communications I use SSL / TLS (https) with client certificate. If I log the entire SSL traffic on the server side, is the SSL log sufficient evidence that the communication between the server and the other side with client certificate was exactly as it is recorded in the log? At the beginning an asymmetric handshake is used but further communication continues with symmetric encryption. Symmetric encryption would not mind if one of the messages cannot be forged on the receiving side. As a server I know the symmetric key so it should be able for me to spoof one of the messages sent by the client, shouldn't it? What algorithm and what special settings shall I use, so that client could not say that he sent a different message than what I recorded in the log?
Logging anything (including data from SSL) does not proof the origin of the data. In theory you've could made up the data yourself. Even logging the complete SSL traffic including the necessary encryption key does not proof anything because in most cases this could have been made up too.
It might be acceptable as a proof if the whole SSL traffic is logged including the encryption key and if a client certificate was used for authentication (i.e. two-way SSL). The real client certificate owned by the client is a part you can not make up yourself. But there is still no guarantee that some judge would accept it as proof. And of course the client could try to deny that this is its own client certificate which was used.
We have a web server running on linux machine where we configured 'SSLVerifyClient' as 'require' in ssl.conf file.
Does this needs client who is utilizing the service from web browser(like firefox or chrome) needs a certificate.
If yes, then it is not possible to distribute client certificate to every user as there can be some thousands of users, how to overcome this problem.
If no, then how the data passed over network is secure? I know that certificate helps in encrypting data so that no one who don't have certificate can read data.
Please help me in clarifying my doubts
If you don't use client certificate, the https connection is still safe:
Only the client and the server can read/write the content
The identity of the server is assured by a certificate authority
Client certificate only give you client authentication in the beginning of the connection. To encrypt the data, the public key of the server is used in the beginning (See public key encryption).
If you identify the client with cookies set after login/password submit, it is still safe: you have identify the client.
When SSLVerifyClient is set to require, the client MUST pass a client certificate. You would generate these via OpenSSL, and sign them with a certificate authority that you install via SSLCACertificateFile.
How you distribute those certificates is an issue you'll have to solve yourself.
I want the ability to prove to a third party (not myself) that I received some given content from a given https server, or in other words, have a signature of that content that can be verified against the public key of the SSL certificate of a website.
According to this, it seems that a signature of the digest of the data is being sent and I am hoping that this is happening every time a page is loaded. If that is right, how/where can I see/extract that signature? (e.g. using curl, whatever command line, tool...)
If my last assumption is inaccurate, is there a way that I can produce the proof described above? And if so, how?
Thanks,
TLS uses data integrity control mechanism, but as the name suggests (TLS = Transport Layer Security), TLS is about protecting the data channel, not about "signing the data". TLS guarantees (or attempts to) that what has been sent via the protected channel remains unchanged in transit and it has not been altered by the third party. So you don't need to manually check any signatures besides the validation procedure performed by the TLS client on your behalf. If you trust your TLS client, then you trust the connection. You can perform additional checks of the certificate sent by the server, but you can't check the "signature of the digest of the data".
It's possible to craft a server which will calculate the signature of the data and put the signature to the response headers, but out of the box I didn't see any server doing this (or any client verifying such signatures).
I'd like to run some encrypted connections between some of my own servers. One can use Curl (or some other mechanism) to connect using HTTPS without SSL certificate verification. I'm using PHP, but the language probably isn't significant for this question.
I'm assuming using HTTPS without a SSL certificate is atleast more secure than doing the exact same connection over plain HTTP, since atleast it's encrypted and an evildoer would have to make a much larger effort to intercept en decrypt the information.
As far as I know an SSL certificate only says "this trusted third party says the server you connect to is owned by the guys that claim to own it". If I connect using my own domainname or IP address, I know I'm the owner. What additional value does an SSL certificate provide if I'm the owner of both ends of a connection?
Not verifying the identity of the server you connect to leaves the connection open to potential MITM attacks. SSL/TLS can be used without certificates (with anonymous cipher suites), but they're insecure (and disabled by default); as the TLS RFC says: "Note that this mode is vulnerable to man-in-the-middle attacks and is therefore deprecated."
In addition, the HTTPS specification itself expects there to be an X.509 certificate.
Checking the identity of the remote party is a necessary element for securing your system. It's not very useful to exchange data secretly with a remote party who may not be who they claim they are (even if the secrecy is guaranteed).
This being said, you don't have to go via a commercial CA. You can either use self-signed certificates, which you would have to import individually into each client as trusted certificate, or create your own institutional CA. There are tools to do this, ranging from OpenSSL's CA.pl (see man-page), TinyCA or OpenCA amongst others. Some operating systems also provide their own small CA capabilities.
If I connect using my own domainname or IP address, I know I'm the
owner. What additional value does an SSL certificate provide if I'm
the owner of both ends of a connection?
The certificate assures you that you're indeed connecting to your machine and that the traffic hasn't been intercepted. That's why you need to check that it's a certificate that you recognise.
SSL certificates are more for the piece of mind of your customers or those using your site. In either case, the data is being transmitted over the same connections - it's just a matter of whether or not a third party is certifying you as being safe.
At my last job, we did all of our internal data transfers at my last job via https/ftps but did not have an SSL certificate until very recently. Since the data transfers were internal, it made no difference.
If one way SSL is used (Server Certificate authentication) then data sent from client gets encrypted using Public key of the server certificate. So privacy protection is available for data sent from client. My questions are
Does this mean that in One way SSL data sent from Server to client is not encrypted and sent as plain text ?
For both server to client and client to server communications the data/message is not signed and so tamper protection or data integrity is not assured. Are there any other means to achieve data integrity while using SSL based transport security and not Message security options ?
One way SSL just means that the server does not validate the identity of the client. It has no effect on any of the other security properties of SSL.
While the SSL protocol is a bit complex, the basic gist of what happens is this: The client generates a random key, encrypts it so that only the server can decrypt it, and sends it to the server. The server and client now have a shared secret that can be used to encrypt and validate the communications in both directions.
The server has no idea of the client's identity, but otherwise, the encryption and message validation is two way.
Update:
1) Yes, encryption both ways is symmetric and uses a shared secret generated during session setup.
2) With a shared secret, message integrity is trivial to assure. You just ensure the message has a particular form. For example, I can prefix every message I send with a sequence number and append a checksum onto it before encryption. You decrypt it with the shared secret and validate the sequence number and checksum. How can an attacker substitute or modify the message without knowing the shared secret and still keep the sequence number and checksum intact?
In SSL, two things happen:
First, a session key is negotiated using something like the
Diffie-Hellman method. That generates a shared session key but never
transmits the key between parties.
Second, that session key is used in a normal symmetric encryption for
the duration of the connection.
SSL does use public/private in one way, because an X509 certificate is
used to identify at least one end of the connection. Those certs are
signed using an asymmetric key pair.
Extracted from How can SSL secure a two-way communication with only one key-pair?