1) The task for which you would not use cryptography is "Plotting data". Cryptography is a technique of secure communication, which includes techniques like encryption, decryption, digital signatures, and user authentication, but it is not related to plotting data.
2) An email application that verifies the sender of an encrypted message is most likely to use asymmetric encryption. Asymmetric encryption is also known as public-key encryption and is commonly used for secure communication over the internet. In this scenario, the sender may encrypt the message with their private key, and the receiver can verify the sender's identity using the sender's public key.
3) Increasing the byte length of a key makes the encryption more secure by increasing the amount of time needed to crack the key. The larger the key length, the more possible combinations there are for the key, making it more difficult for an attacker to guess or crack the key. This is because the larger the key size, the more computational effort is required to try all possible combinations of the key, making it infeasible to crack the key within a reasonable time frame.