How an error in ciphertext transmission affects the deciphered plaintext. It is often studied a 1-bit change ("bit flip") of the ciphertext. That could induce a bit flip in the plaintext, a larger plaintext alteration, or an impossibility to decipher. For a block cipher, error propagation is a characteristic of the mode of operation; e.g. a ciphertext bit flip affects 2 blocks of plaintext for CBC, all subsequent blocks for PCBC.