Crunching the numbersįirst, I find two huge (at least 100 digits each!) prime numbers p and q, and then I multiply them together to get the even bigger number N. The mathematical difficulty of the above problem is what ensures the strength of our encryption (or lock). Which two prime numbers did I multiply together to get 194477? A computer can probably unlock this number easily, but not if the prime numbers I use are much larger. This is called a trapdoor, meaning it’s easy to go one way, but very hard to go the other. It’s easy for a computer to multiply two large prime numbers together (Google will do this without breaking a sweat).īut let’s say you multiply two large prime numbers together to get a resulting number: if you gave this new number to a computer and asked it to tell you what prime numbers you multiplied to construct it, the computer would struggle. The algorithm’s design and strength are the work of historic results in number theory, and its security is guaranteed by the following fact: Now we get into the RSA algorithm, which is the strongest possible way to encrypt and decrypt information online. So how do we know Alice and Bob’s online communications aren’t being monitored by Eve? These days, of course, more people opt for email rather than snail mail. This will be a safe transmission, seeing as Bob is the only one with the key.īut what a complicated way of securing information: for people to receive secret messages, they need to have public padlocks available to everybody! If Alice wants to send Bob a secret message, she simply needs to go to Bunnings and get one of these open padlocks, then use it on the box she wants to send Bob. Bob unlocks all of these padlocks and makes them available at, say, Bunnings. One solution to this problem runs in parallel with the RSA algorithm.īob knows people (Alice, in particular) want to send him secret messages, so he goes out and buys a stack of identical padlocks, all of which open with a single key he keeps hidden in his left shoe.
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