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.

with a convertor :P

In diffusion, the statistical structure of the plaintext is dissipated into long-range statistics of the ciphertext. This is achieved by having each plaintext digit affect the value of many ciphertext digits, which is equivalent to saying that each ciphertext digit is affected by many plaintext digits. Confusion seeks to make the relationship between the statistics of the ciphertext and the value of the encryption key as complex as possible, again to thwart attempts to discover the key. Thus, even if the attacker can get some handle on the statistics of the ciphertext, the way in which the key was used to produce that ciphertext is so complex as to make it difficult to deduce the key. This is achieved by the use of a complex substitution algorithm.

Ciphertext is another name for Encrypted