Attribute-based encryption (ABE) is a promising technique for fine-grained access control of encrypted data in a cloud storage, however, decryption involved in the ABEs is usually too expensive for resource-constrained front-end users, which greatly hinders its practical popularity. In order to reduce the decryption overhead for a user to recover the plaintext, Green et al. suggested to outsource the majority of the decryption work without revealing actually data or private keys. To ensure the third-party service honestly computes the outsourced work, Lai et al. provided a requirement of verifiability to the decryption of ABE, but their scheme doubled the size of the underlying ABE ciphertext and the computation costs. Roughly speaking, their main idea is to use a parallel encryption technique, while one of the encryption components is used for the verification purpose. Hence, the bandwidth and the computation cost are doubled. In this paper, we investigate the same problem. In particular, we propose a more efficient and generic construction of ABE with verifiable outsourced decryption based on an attributebased key encapsulation mechanism, a symmetric-key encryption scheme and a commitment scheme. Then, we prove the security and the verification soundness of our constructed ABE scheme in the standard model. Finally, we instantiate our scheme with concrete building blocks. Compared with Lai et al.'s scheme, our scheme reduces the bandwidth and the computation costs almost by half. IndexTerms-Attribute-based encryption, outsourced decryption, verifiability, access control.

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The neurocognitive basis of the effect of long-term high altitude exposure on voluntary attention is unclear. Using event related potentials, the high altitude group (people born in low altitude but who had lived at high altitude for 3 years) and the low altitude group (living in low altitude only) were investigated using a voluntary spatial attention discrimination task under high and low perceptual load conditions. The high altitude group responded slower than the low altitude group, while bilateral N1 activity was found only in the high altitude group. The P3 amplitude was smaller in the high altitude compared to the low altitude group only under high perceptual load. These results suggest that long-term exposure to high altitudes causes hemispheric compensation during discrimination processes at early processing stages and reduces attentional resources at late processing stages. In addition, the effect of altitude during the late stage is affected by perceptual load. More than 140 million people live permanently at high altitudes (.2,500 m above sea level) in North, Central, and South America, East Africa, and Asia 1 . As of 2006, approximately 12 million people live permanently on the Qinghai-Tibetan Plateau, and 71.14% of them live between 2,500 to 4,500 m. In addition, hundreds of thousands of people travel from lowland China to the Tibetan plateau every year; about 6 million Han lowland immigrants now live there permanently 2,3 . The largest and most important impact of living in a high altitude is hypoxia, which is caused by a reduction of oxygen in the air, and affects cognition. Sustained exposure to high altitude leads to cognitive decrement, such as impairment in attention, memory, judgment, and emotion 4 . Research has demonstrated that cognitive impairment due to altitude starts at 2,500 m above sea level [5][6][7] , because brain vulnerability to hypoxia increases beginning at 2,500 m 8 . Spatial attention may be particularly affected by high altitude exposure. First, the attentional impairment caused by exposure to high altitudes has been found in behavioral tests of visual attention (e.g., the digit symbol substitution test and visual search task) 9,10 , with slowed reaction times at higher altitudes. Second, previous studies have provided neuroimaging and electrophysiological evidence of the impact of high altitude exposure on the human brain [11][12][13] . In the neuroimaging study, brain areas related to attention processing-including the occipital lobe, parietal lobe, sensory-perceptual regions and frontoparietal attentional networks-were found to be affected by high altitude exposure 13,14 . In the electrophysiological study, the parietal distributed P3, which is crucially involved in maintaining attention, was the event-related potential (ERP) component most significantly affected by hypoxia 11,15 . Specifically, smaller and later P3 component responses have been reported for participants at high altitude than in those at the low altitudes, suggesting that cognitive abilities are sensitiv...