What type of certificates or keys are exchanged between a client and a server when it loads a webpage or website ?
Only the server's public key and the client's public key are exchanged.
The following occurs when a browser is connection to an HTTPS enabled website / service:
Client Hello
The client sends the SSL version number, cipher settings, session-specific data.
Server Hello
The server responds with the SSL version number, cipher settings, and the Server’s Certificate (Public Key).
Authentication and Pre-Master Secret
The client now authenticates the server certificate, and depending on the cipher the client creates a pre-master secret for the session.
The client encrypts data with the server's public key and sends the encrypted pre-master secret to the server.
Decryption and Master Secret
The server now uses its private key to decrypt the pre-master secret.
Both the server and client perform steps to generate the master secret with the agreed cipher.
Generate Session Keys
Both the client and the server now use the master secret to generate the session keys. The session keys are symmetric keys used to encrypt and decrypt information exchanged during the session.
Encryption with Session Key
At this point both server and client exchange messages to inform that future messages will be encrypted.
In short, there are 4 keys involved. The server's public and private key and the client's public and private key. The client gives it's public key to the server and the server gives it's public key to the client. The private keys are never transmitted or shared with anyone, they remain on the client and server, thus they are private.
Usually certificates are signed by a third party such as GoDaddy or Verisign. This gives the client reassurance that the server who issued the public key to the client is indeed who they say they are. (However beware, there is always the possibility of man in the middle attacks)
Related
I understand the use case of Asymmetric Encryption using a private and public key. A client side Web Application can encrypt a JWE using a servers public key and the server uses its private key to decrypt the encrypted message.
Is it possible for a Web client to receive an encrypted message from a server encrypted by the Web Clients public key and have its own private key to decrypt the servers encrypted message?
From what I understand about security the browser is not a safe place to hold keys since an experienced person can read them if they wanted.
So is the encryption and decryption with JWE only possible in one (server to client) direction? Or is it possible for a Web client to hold a private key for decryption for encrypted messages from a server safely?
I'm doing my best to understand mutual SSL. One question I can't find a good answer to is why you need to create a key pair on the client instead of just providing a public client certificate.
So far I understand the following (very oversimplified):
Regular SSL:
The server has a key pair and sends the public part (certificate) so the client can use that public key to encrypt messages so they can share a symmetric key and eventually secure all communication.
To verify that the server is actually the server the issuer of the certificate has to be trusted (in a truststore) of the client by default.
Mutual SSL:
Exactly the same, only this time the server asks the client to authenticate itself.
The client sends its public certificate, which is verified against some kind of list of "known certificates" on the server. If it matches, communication can continue.
I don't understand why I have to include the entire key pair (the private part as well) in the key store I use on the client side. Where is the client's private key used in the process?
The server has a key pair and sends the public part (certificate) so the client can use that public key to encrypt messages so they can share a symmetric key and eventually secure all communication.
That's not the main point of the server certificate and with modern key exchange methods (i.e. Diffie-Hellman) the certificate is not involved at all in the key exchange. What you describe is only true for the obsolete RSA key exchange.
The main point of the certificate is to be used for authentication. Authentication means that the server proves that it owns the provided certificate and then that the client verifies that the certificate matches its expectations, i.e. issued by a trusted CA, expected subject/SAN, not expired etc.
The proof of ownership is done by signing some data (which is at least in part provided by the peer, i.e. client) with the private key matching the public key in the certificate. The peer (client) then can verify this signature using the public key of the certificate and if the verification passes the other side (server) is obviously in possession of the secret private key which means it owns the certificate.
With a client certificate used in mutual authentication the procedure is exactly the same, only with switched roles. That's why the private key is needed on the client side.
I aks myself if it is possible to copy the server certificate to another server to misuse it. Example: An attacker visits https website X and copies the X.509 certificate. He placed the stolen X.509 certificate on his own server and would like being trustworthy.
Of course, the attacker does not have the private key, but the private key is only required to decrypt the encrypted message from the client. In terms of authentification there is no reason to be doubtfully. Or?
The server responses with the X.509 certificate. The client receives the certificate and validates successfully using the stored root certificates. Why should the server not be authentificated? Only when the client sends an encrypted message using the public key the server is not able to decrypt the message - because he does not own the private key.
It is right so far?
Only when the client sends an encrypted message using the public key the server is not able to decrypt the message - because he does not own the private key.
The server also needs the private key to sign messages being sent to the client.
The SSL/TLS handshake protocol itself effectively involves such an authenticated message being sent to the client. If the private key is unavailable then this step will fail before any 'real' payload message gets sent.
Why should the server not be authentificated?
The certificate is tied to a domain name.
The web browser will download the certificate and validate it. One of the steps in the validation is to compare the domain the certificate is for to the domain that the browser actually downloaded it from. If there is a mismatch (and there will be, since the attacker is on their own domain, not the original site's domain) then the browser will present the user with a certificate error and ask them to make the call about whether or not to accept it.
You're probably used to seeing this in action on bad web server configurations. Ever seen an error saying, "This certificate was intended for www.example.com" when you were trying to visit "example.com"?
Of course, the attacker does not have the private key, but the private key is only required to decrypt the encrypted message from the client.
Public/private key pairs have other uses than that. In this case, the private key signs the certificate and the public key verifies it. There is no encryption involved. (What you described is more like a normal encryption scheme, like RSA.)
No, the certificate is a pubic element and it is just a way to bind a public key to a name (here, a DNS name). During the authentication process (in the TLS protocol) the server sends its certificate along with signs some data with the associated private key. In order to verify that the server is the legitimate owner of the certificate, the client have to verify the validity of this signature with the sent certificate. A rogue server can try to use the certificate but without the private key it cannot prove it is the real holder.
I have a tcp server and using cms/pkcs#7 to secure the message passed between the client and server. Would it be normal practice to pass the clients public key to the server, as part of initial session? As its the public key, when the session starts up, the initial clp command, would pass the key, along with other salient details that the server needs to know about the client. It's the public, so it doesn't need to be encrypted, it public.
The client/server communication is secured with ssl/tls.
Thanks.
Bob.
Don't you trust SSL/TLS or why do you encrypt again within the secure channel? That only makes sense if the server will pass the message on to other nodes and it will be decrypted somewhere else, thereby creating end-to-end security.
In any case, you should not have the client pass just the public key to the server. Instead it should pass a certificate to the server, which should authenticate the client based on a signature made with the private key matching the public key contained in the certificate. Also, the server will need to check the certificate itself (is it from a trusted CA, do the signatures in the chain verify, etc.).
If you can, you should do all this on the SSL/TLS layer by using SSL/TLS mutual authentication (client cert authentication). If you cannot, then make sure you design a secure application layer protocol for authenticating the client and it's public key. Otherwise it may be possible to impersonate other clients.
According to X.509 standard private key signature has to generate same encrypted message for ever?Am I right?
In order to avoid coping which data field in digital certificate will be changed?
they can't process the information of the user, but by coping the digital signature generated by private key and keeping along with the webpage attacker can say that I am certified by the CA and web browser will agree with that information.Is it true?
Version number,Serial number,Certificate algorithm identifier,Issuer name,Validity period,Subject name,Subject public key information Issuer unique identifier,Subject unique identifier,Extensions,Certification authority's digital signature.
These are the fields in digital certificate,if this fields don't change for ever,encrypted value will be same for ever.If I go to gmail it sends Encrypted digital certificate.If I use that Encrypted digital certificate in my webpage cant I say I am owner of gmail.but I can't use information send by the user since I won't have private key
A certificate must be signed by a CA in order to be considered as valid. The contents of the certificate is hashed, then encrypted by the CA's private key. Anyone can then validate whether the certificate is valid by decrypting the signature with the CA's public key, and verifying whether the hash matches.
The signature verifies that a particular name is associated with a particular public key - even if someone copied the certificate file verbatim, they wouldn't know the private key corresponding to that public key, and so they couldn't use it to impersonate the owner of the certificate.
I was wondering the same question.
Reading #Anon.'s answer led me to this: https://en.wikipedia.org/wiki/Transport_Layer_Security#Description
The handshake begins when a client connects to a TLS-enabled server
requesting a secure connection and the client presents a list of
supported cipher suites (ciphers and hash functions).
From this list, the server picks a cipher and hash function that it
also supports and notifies the client of the decision.
The server usually then sends back its identification in the form of a
digital certificate. The certificate contains the server name, the
trusted certificate authority (CA) that vouches for the authenticity
of the certificate, and the server's public encryption key.
The client confirms the validity of the certificate before proceeding.
To generate the session keys used for the secure connection, the
client either:
encrypts a random number with the server's public key
and sends the result to the server (which only the server should be
able to decrypt with its private key); both parties then use the
random number to generate a unique session key for subsequent
encryption and decryption of data during the session or
uses Diffie-Hellman key exchange to securely generate a random and unique
session key for encryption and decryption that has the additional
property of forward secrecy: if the server's private key is disclosed
in future, it cannot be used to decrypt the current session, even if
the session is intercepted and recorded by a third party.
It looks like in your forgery example (that I was wondered also) the client confirms the certificate successfully in paragraph 4. And then in paragraph 5 they fail to agree on session key as the server cannot read client's random number.