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The RSA algorithm is used for encryption (plain text to cipher text) and decryption (cipher text to plain text) of data. What is the need for using public keys in these sites; why is data is encrypted as everything is viewed by everyone?

Why do we need to use public key cryptography in Google; how does it provide security?

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Welcome to Cryptography.SE. You question would be clearer if you described which uses of RSA by Google you are talking about (i.e. are you discussing it's use in HTTPS/TLS, or other uses?). –  archie Jul 16 '13 at 1:12
    
Why is this tagged post-quantum-cryptography –  user93353 Jul 16 '13 at 11:56

2 Answers 2

[I assume you're talking about Google's web search service, and not Gmail.]

Google doesn't encrypt the web page data in storage, because it's not secret data. Encryption is optionally used by users to securely communicate with Google, and that's different.

Using certificate based keys and encryption assures the users that they are communicating with the Real Google and not a Fake Google that could give them false results. It also protects the users' privacy from eavesdroppers; so if someone was searching for 'cancer' their employer or family wouldn't know.

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When you go to google.com - it seems to redirect it to google.com - I think OP is referring to that. - ghacks.net/2011/10/23/… –  user93353 Jul 16 '13 at 10:38

Google explains here why they redirect your search to https.

As search becomes an increasingly customized experience, we recognize the growing importance of protecting the personalized search results we deliver. As a result, we’re enhancing our default search experience for signed-in users. Over the next few weeks, many of you will find yourselves redirected to https://www.google.com (note the extra “s”) when you’re signed in to your Google Account. This change encrypts your search queries and Google’s results page. This is especially important when you’re using an unsecured Internet connection, such as a WiFi hotspot in an Internet cafe.

Facebook, GMail etc have a login username/password. So there one of the reasons for https is so that your password doesn't go in clear text. As to why these sites do end to end https rather than using just https for the username/password part - you can see this Q & A here.

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