a virus) to capture the symmetric keys when they are generated.
Wireshark use certificate software#
Use specially crafted or malformed certificates to fool the browser (and its weak implementation) into thinking that a public key is signed by a trusted entity when it's really not.Ĭompromise the integrity of the client software (e.g. While there have been weak SSL algorithms (hence the succession of SSL protocol versions), these days the attacks are generally targeted to the implementations:
and not, say, some criminal's laptop in the next cafe table that is messing with the wireless connection. Since each public key was successively signed until we reached a trusted key, the client can now be certain that the server on the other end of the connection is indeed e.g. You might want to read a previous answer of mine for more on Root Certificates, or just read the Wikipedia articles. That certificate pair would be likewise be signed by another and so on, until the browser comes up to a public key that was signed with the private key that corresponds to one of the Root Certificates that were preinstalled with it. So when the browser contacts a server and receives its public key, that key should be signed with the private key from a certificate pair. The Certification Authorities use the corresponding private keys to sign other public keys available in the Internet and so on. Those belong to Certification Authorities (CA) that are entities (generally companies like Verisign, governments or even some Institutions) that are deemed trustworthy. When the browser is installed it has a relatively small number of public keys (commonly known as certificates) pre-installed. Essentially we sign the data so that if decrypts with the public key people will know the data came from the server. Now weĭo the opposite: We use the private key to encrypt data so that it can only be decrypted with the public key. Previously we used the public key to encrypt data so that only its intended destination could descrypt it. This is where another function of Public Key Cryptography comes in. It will have to retrieve them from the servers and then somehow make sure they belong to the server they are interested in.
The client cannot possibly know every single public key - there are millions of them. Is it? There is still one issue in the above scheme! How will the client get the server's public key? More specifically how does it know that it speaks with the server proper, and not some crook who managed to insert themselves in the middle (See Man In The Middle attack)? The server uses its private key to retrieve the session symmetric key and all is well. That means that it cannot be extracted from a captured network stream, and since it is used for the rest of the session, neither can any of the information that is transmitted later on. Since the symmetric key is encrypted like this, it can only be decrypted using the server's private key. The client uses the server's public key to encrypt a rather long random key for a symmetric algorithm at the start of each encrypted session. The server has a key pair that consists of a world-readable public key and a securely stored (and inaccessible to anyone but the server itself) private key. The public key is widely accessible to "everyone" while the private key is stored securely and only used by its owner. Assuming a sufficiently strong algorithm, whatever is encrypted with the public key can only be encrypted with the private one and vice versa. Those involve two keys, rather than one, a public key and a private key. Public Key Cryptography is based on asymmetric encryption algorithms. I will add some more information in layman terms, mostly ripped off from the two links above, to make things a bit more clear. See also the Wikipedia article on TLS for more information. You would need the private keys of the server in order to descrypt an SSL session and in normal situations it is quite hard to acquire those. Said public keys are accessible, but they cannot be used to decrypt the session packets because the encryption algorithm is not symmetric. What you have in your browser key-store is the certificates that will verify the validity of the public keys of the server. That is the whole point of Public Key Cryptography on which SSL is based.
No, you cannot decrypt HTTPS/SSL sessions from a network capture, even if you do have the certificates.
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