For some keys, an all-zero initialization vector may generate some block cipher modes (CFB-8, OFB-8) to get the internal state stuck at all-zero. For CFB-8, an all-zero IV and an all-zero plaintext, causes 1/256 of keys to generate no encryption, plaintext is returned as ciphertext. For OFB-8, using all zero initialization vector will generate no encryption for 1/256 of keys. OFB-8 encryption returns the plaintext unencrypted for affected keys.
For some keys, an all-zero initialization vector may generate some block cipher modes (CFB-8, OFB-8) to get the internal state stuck at all-zero. For CFB-8, an all-zero IV and an all-zero plaintext, causes 1/256 of keys to generate no encryption, plaintext is returned as ciphertext. For OFB-8 using all zero initialization vector will generate no encryption for 1/256 of keys. OFB-8 encryption returns the plaintext unencrypted for affected keys.