How does SSL work? What is an SSL handshake?

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SECURITY TOPICS

How Does SSL/TLS Work?
What Is An SSL/TLS Handshake?

SSL/TLS are protocols used for encrypting information between two points. It is usually between server and client, but there are times when server to server and client to client encryption are needed. This article will focus only on the negotiation between server and client.

Server and Client Negotiation

For SSL/TLS negotiation to take place, the system administrator must prepare the minimum of 2 files: Private Key and Certificate. When requesting from a Certificate Authority such as DigiCert Trust Services, an additional file must be created. This file is called Certificate Signing Request, generated from the Private Key. The process for generating the files are dependent on the software that will be using the files for encryption. For a list of the server softwares DigiCert has, look at: DigiCert CSR Generation.

Note that although certificates requested from Certificate Authorities such as DigiCert are inherently trusted by most clients, additional certificates called Intermediate Certificate Authority Certificates and Certificate Authority Root Certificates may need to be installed on the server. This is again server software dependent. There is usually no need to install the Intermediate and Root CA files on the client applications or browsers.

Once the files are ready and correctly installed, just start the SSL/TLS negotiation by using the secured protocol. On browser applications it is usually https://www.DigiCert.com. Remember to use your secured website address. Above is just a sample address.

The Standard SSL Handshake

The following is a standard SSL handshake when RSA key exchange algorithm is used:

1. Client Hello

Information that the server needs to communicate with the client using SSL. This includes the SSL version number, cipher settings, session-specific data.

4. Decryption and Master Secret

Server uses its private key to decrypt the pre-master secret. Both Server and Client perform steps to generate the master secret with the agreed cipher.

2. Server Hello

Information that the server needs to communicate with the client using SSL. This includes the SSL version number, cipher settings, session-specific data.

5. Encryption with Session Key

Both client and server exchange messages to inform that future messages will be encrypted.

3. Authentication and Pre-Master Secret

Client authenticates the server certificate. (e.g. Common Name / Date / Issuer) Client (depending on the cipher) creates the pre-master secret for the session, Encrypts with the server's public key and sends the encrypted pre-master secret to the server.

Negotiation Tools

OpenSSL

Learn more about tools such as OpenSSL used during SSL/TLS negotiations.

Click below to view the sample code used in an SSL handshake.

LEARN MORE

Client Certificates vs. Server Certificates What’s the Difference?

Mention PKI or ‘Client Certificates’ to many people and it may well conjure up images of businesses busily protecting and completing their customers’ online transactions, yet such certificates are to be found throughout our daily lives, in any number of flavors; when we sign into a VPN; use a bank card at an ATM, or a card to gain access to a building; within Oyster public transport smart cards, used in central London.

Renewing SSL/TLS Certificates

One of the easiest ways you can protect your visitors’ information is to make sure you renew your SSL/TLS certificates on time.

What Is EV SSL?

DigiCert SSL/TLS Certificates with Extended Validation (EV) provide solutions that allow companies and consumers to engage in communications and commerce online with confidence.