In Magic the card game, are artifacts always in effect even if the creature blocks?

Example, I have a 5/5 creature with cloak and dagger artifact that gives the creature shroud (it cant be the target of spells or abilities).

A friend of mine likes oblivion ring which pretty much takes the card out of the game. His interpretation is that when I block, I loose the shroud ability? Therefore he is able to use the oblivion ring on the creature. Is that

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