Question

Hey guys! This is some homework I found from last year to help me prepare for our upcoming test.

Can yall help?

3-(20 points) We discussed a public key cryptographic system in class which allows two people who did not meet to exchange messages secretely. But the first step, obtaining each other's public key is at risk. For example, l can hispublish my public key on a billboard on highway 72 and say t it is the key of Kay Ivy and please send money. Someone wanting to give kay ivy money would send it to me. How is this prevented in today's world. That is, ifi was worried about someone publishing a false public key, how could i do it if I did not want to meet them in a secret place (like when you met your phone to give it a shared secret)

Answer 1

Answer)

Cryptography is the art of secret writing. In cryptography, the plain text is converted into non-human readable cipher text. There are 2 processes in cryptography such as encryption and decryption. Encryption means converting plain text to cipher text and decryption means converting the cipher text back to human readable and meaningful plain text. To make a message or content secure we apply cryptographic algorithms so that the message cannot be read or meaning cannot be understood by persons for which it is not meant to.

Only authorized persons will have the means of decrypting the cipher text back to plain text so that they can understand the meaning of it. When sending through an unsecured medium of transmission such as the internet cryptographic algorithms are used to secure the transfer of messages from the source to the destination.

There are generally 2 types of cryptographic techniques: symmetric key or private key cryptography and asymmetric key or public key cryptography. The private key cryptography means that a message has to be encrypted with a key from the sender to the receiver. The message will be encrypted using the key at the source and also be decrypted at the destination using the same key. Here the key sharing is the problem over the unsecured medium as much as message sharing. Thus there is a problem.

Another type of cryptography is the public key cryptography, where the sender and receiver have a public and private key. Here the public key is broadcasted while the private key is private to the party. Messages are encrypted with the receiver's public key, when the receiver receives the encrypted message the message is decrypted using the private key of the receiver.

Now the thing of the concern is if we could fake public keys, then we can pose to be another person and thus this will be an security issue. Here the security issue is overcome using a digital signature to identify the sender and the message. Then sender can combine the message with a private key to create a short digital signature on the message, and the intended receiver can combine a message, the digital signature which is received and the public key which is known to the public to verify that the signature was valid and thus the sender can be trusted. The authenticity of the message is kept authentic by the sender by the digital signature as the sender keeps the private key safe and secret. Changing the message or anything in the transmission will lead to a digital signature mismatch and thus we won't be able to fake it.