If the message is intercepted on the way by a third party, they will only have unreadable data and will have gained nothing, unless they can figure out the decryption algorithm and obtain the key. This is why the key is never to be sent with the message, and has to be kept secret at all cost. If the key is compromised, the sender and the encrypted data is no longer safe. The sender and the receiver then usually agree on a new key to prevent any further damage.

In ancient Greece, around 550 Bc, messages were sent encoded to generals and could only be deco

Finally, one of the most useful uses of cryptography that we might all find use for is "Digicash". Without cryptography it is very close to impossible to implement a successful and convenient scheme for online money. And online money is something most online businesses and shoppers would love to have.

In France during 1585, members of the king's court liked to send romantic or gossip messages to each other and encrypt them for safety, which becomes almost a necessity. Blaise de Vigenere came up with a poly-alphabetic substitution known as the Vigenere cipher. Basically, the algorithm would encrypt messages several letters at a time instead of letter by letter. For example ab = fh, th = sq. To simplify the huge keys it would require, the key was broken into a table and a key, the table was fairly big but the key was small enough to be memorized, and the table was useless without the key. This cipher wasn't totally safe but no totally sure method to break it was developed before early in the 20th century.

1. Stealing the key! (and don't let them know you have it). This is the simplest and most radical way of breaking into someone's secret transmissions.

This is where digital signatures come in handy. They allow a person to sign a message in a way that certifies that the message was actually sent by them. This is done by using one other interesting property of the private and public keys in RSA: they can be reversed in the algorithm and it will still work. For example, if you encode something using the private key, it can be decoded with and only with the public key. So when Jack sends something to Bob, he takes "signed Jack" and encrypts it with his private key (note that this in no way reveals what his private key is) and adds that at the end of his message as a signature. When Bob receives the message from Jack and decrypts it, he will obtain a small encrypted piece of data at the end of the message, which is the encrypted signature Jack put there. Bob can decrypt it with Jack's public key, and if a real message comes out of it, (i.e: not a series of apparently random numbers) then he knows that Jack was indeed the person that sent him the message. Usually, people add the exact time and date inside their signature to make sure each signature can be used only once. That is, once Bob has Jack's signature at the end of the message, he can't send a message to Tom that says:

Monoalphabetic substitution is another simple step away from the ROT13 algorithm. In this algorithm, each letter correspond to another letter but in no particular order. For example a = d, d = x, f = e, etc for all 26 letters. This made it much harder to break but also made fairly big keys that couldn't be memorized, since they consisted of 26 pairs of letters.

Some common words found in the essay are:
Digital Money, Data Breaking, Key Cryptography, Stephen Vwhskhq, , Remember Internet, Michael Grubb's, Jack Joe, Note RSA, Algorithm RSA, public key, private key, digital signatures, third party, rsa algorithm, public key cryptography, decryption algorithm, key cryptography, digital money, sender receiver, sent message, digital signature encrypted, algorithm based prime, wuss signed jack, you're wuss signed,
Approximate Word count = 3131
Approximate Pages = 13 (250 words per page double spaced)