Besides dissimulation (noun, “The act of concealing the truth; hypocrisy or deception”), consider masquerade as a noun, “Acting or living under false pretenses; concealment of something by a false or unreal show; pretentious show; disguise”, or as a verb, “To frolic or disport in disguise; to make a pretentious show of being what one is not [eg] He masqueraded as my friend until the truth finally came out”.
Note, dissimulation occurred to me before I saw it in your question; it is ok; however, the word I thought of before that was verb dissemble (“To disguise or conceal something; to feign”). A related word is sham, which as an adjective, noun, or verb has meanings like intended to deceive; false; fake; an imitation that purports to be genuine; to deceive, cheat, lie. Another is counterfeit, with similar meanings.