What term describes the property where a change in one bit of plaintext affects multiple characters in the ciphertext?

The term that describes the property where a change in one bit of plaintext affects multiple characters in the ciphertext is diffusion. This concept is crucial in encryption algorithms, as it ensures that even small changes to the plaintext result in significant and widespread changes in the ciphertext. This property enhances security by making it more difficult for an attacker to discern relationships between the plaintext and ciphertext.

When diffusion is effectively implemented in an encryption scheme, it means that the entire structure of the ciphertext can change dramatically with just a single bit modification in the plaintext. This characteristic acts to obscure any patterns that may exist in the plaintext, thereby reducing the likelihood of successful cryptanalysis.

In contrast, while the avalanche effect is related and sometimes used interchangeably with diffusion, it specifically refers to the concept whereby a small change in input results in a significant change in output, particularly focusing on the output of an encryption algorithm rather than the relationship between plaintext and ciphertext as a whole.