The kind of attack you are referring to is known as a known-plaintext attack. In this type of attack, the attacker has access to both the plaintext and the corresponding ciphertext, and the goal is to deduce the encryption key or algorithm used. By analyzing the patterns or relationships between the known plaintext and ciphertext, the attacker can potentially uncover vulnerabilities in the cryptosystem.

The result of encryption of plaintext is cyphertext. When cyphertext is translated back to plaintext, the process is called decryption.

Plaintext is easily readable or, to be more accurate, decrypted/unencrypted text.

This is opposed to ciphertext, which is encrypted.

If you used an encryption algorithm to encode your message of "Hello, there" to "4hgu28fhdjf83291".

The plaintext form would be: "Hello, there"

The ciphertext form would be: "4hgu28fhdjf83291"

with a convertor :P

The last ciphertext block of the previous record. It is is sometimes xor'd with the plaintext of the next record to ensure duplicate plaintext does not encrypt to duplicate cipher text.