Blood pressure (BP) is usually measured either invasively, by an intra-arterial catheter, or noninvasively, by a cuff-based sphygmomanometer. While the invasive method is continuous and more accurate, it has the risk of infection and generally is not comfortable for the patient. On the other hand, the cuff-based measurement is safer but less reliable and infrequent. Therefore, a reliable continuous noninvasive BP measurement is highly desirable. In this work, we propose a remote optical system, based on temporal analysis of secondary reflected speckle patterns, for computing a subject's pulse transit time (PTT). Afterward, a model is proposed and clinically validated for converting the PTT value into systolic and diastolic blood pressure. A full statistical analysis is performed over a comparison to a reference device (SOMNOtouch).