Scan-based design for test(DFT) is a powerful and the most popular testing technique. However, while scanbased DFT improves test efficiency, it also leaves a side channel to the privacy information stored in the chip. This paper investigates the side channel and proposes a simple but powerful scan-based attack that can reveal the key and/or state stored in the chips that implement the state-of-the-art stream ciphers with less than 85 scan-out vectors. Scan-based design for test (DFT) is a powerful and the most popular testing technique. However, while scanbased DFT improves test efficiency, it also leaves a side channel to the privacy information stored in the chip. This paper investigates the side channel and a simple but powerful scan-based attack that can reveal the key and / or state stored in the chips that implement the state-of-the-art stream ciphers with less than 85 scan-out vectors.