OFB means you feed the output of the cipher back to the input. Hence if you have two character sequences that share a prefix e.g. "abc123" and "abcxyz" the firs

OFB means you feed the output of the cipher back to the input. Hence if you have two character sequences that share a prefix e.g. "abc123" and "abcxyz" the first three cipher stream bits will be identical and then deviate based on the feedback the cipher gets (assuming no IV and identical key). This is interesting for pseudonymization when you want to e.g. create cryptographically secure pseudonyms that preserve prefixes (think IP address pseudonyms that preserve subnet groupings).