The WEP secure channel works by sending $$IV||(m||CRC(m) \oplus RC_4(K,IV)$$ where IV is an asynchronous initial vector, K is an encryption key and CRC is a cyclic redundancy check function.
I know there are lots of attacks on this scheme. I also know that this scheme does not protect confidentiality, integrity or sequentiality. However what is meant when we say that in certain way it protects authenticity? The text I'm reading says:
Message authenticity in WEP is not specically protected by a message authentication code. It is protected in the sense that an adversary cannot push a message which makes sense with an unused IV without knowing K. It is enough to know one plaintext and ciphertext to reuse the IV.
Why is authenticity protected in some sense but not integrity? To be honest the last two sentences of the last quotation make no sense to me.