There are lots of ways to break the Caesar Cipher, but one way is to try out all 26 possible keys. PZAOL ILZAA OHAJV YWVYH SIVII FZOHM AVLJH UKVVU ZOVYA UVAPJ L Here's a Caesar Shift with a key of 7 (each letter is moved up in the alphabet 7 places): ISTHE BESTT HATCO RPORA LBOBB YSHAF TOECA NDOON SHORT NOTIC E In that case, the key is the number of places to shift letters and there are 26 possible keys (which is roughly like saying the Caesar Cipher has a roughly 5-bit key). When children use a Caesar Cipher (shifting each letter in the alphabet some fixed number of places) they are performing symmetric cryptography. Symmetric cryptography is the oldest form there is. In one case, a 128-bit key is used, in another a 256-bit key. Symmetric simply means that the same key is used to encipher and decipher the encrypted web traffic. The RC4_128 and AES_256_CBC schemes mentioned above are symmetric cryptographic schemes. To understand these key lengths it's necessary to understand a little about the actual encryption schemes they are used with. It's not uncommon to see RSA with a 1,024-bit key as well. For example, when I connect to the British Government portal gov.uk I get a TLS connection that uses AES_256_CBC (with a 256-bit key) set up using RSA with a 2,048-bit key. You might also have seen other key lengths in use. Key and an asymmetric cipher (ECDHE_RSA) with a 2,048-bit key. My connection above used a symmetric cipher (RC4_128) with a 128-bit This blog post will explain why a 128-bit symmetric key is, in fact, a bit more secure than a 2,048-bit asymmetric key you have to look at both the type of encryption being used (symmetric or asymmetric) and the key length to understand the strength of the encryption. And you'd be forgiven for wondering why a large key wasn't used throughout and whether a 128-bit key is weaker than a 2,048-bit key. If you're not familiar with the cryptographic protocols involved you might be wondering why one part uses a 128-bit key and another a 2,048-bit key. When I connect using Chrome I get an RC4_128 connection (with a 128-bit key) which used the ECDHE_RSA key exchange mechanism (with a 2,048-bit key) to set the connection up. If you connect to CloudFlare's web site using HTTPS the connection will be secured using one of the many encryption schemes supported by SSL/TLS.
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