Error Free Perfect Secrecy Systems

Shannon's fundamental bound for perfect secrecy says that the entropy of the secret message cannot be larger than the entropy of the secret key initially shared by the sender and the legitimate receiver. Massey gave an information theoretic proof of this result, however this proof does not require independence of the key and ciphertext. By further assuming independence, we obtain a tighter lower bound, namely that the key entropy is not less than the logarithm of the message sample size in any cipher achieving perfect secrecy, even if the source distribution is fixed. The same bound also applies to the entropy of the ciphertext. The bounds still hold if the secret message has been compressed before encryption. This paper also illustrates that the lower bound only gives the minimum size of the pre-shared secret key. When a cipher system is used multiple times, this is no longer a reasonable measure for the portion of key consumed in each round. Instead, this paper proposes and justifies a new measure for key consumption rate. The existence of a fundamental tradeoff between the expected key consumption and the number of channel uses for conveying a ciphertext is shown. Optimal and nearly optimal secure codes are designed.Comment: Submitted to the IEEE Trans. Info. Theor

Influence of Baseball Catcher Mask Design, Impact Location and Ball Trajectory on Head Acceleration

International Journal of Exercise Science 9(5): 567-575, 2016. The general aim was to contrast accelerations caused by baseball impacts for different catcher mask designs. Study1 focused on impact locations for a perpendicular ball trajectory. Study2 examined perpendicular and oblique trajectories striking a single mask location. A 5.9 kg head model instrumented with a 3-d accelerometer recording at 512 Hz was mounted upright with springs in a shallow ball joint. A pitching machine fired a standard baseball at ~28 m/s for all tests. Transverse plane resultant peak acceleration was gathered from 5 trials in each experimental combination. In Study1, effects of mask design (T=traditional, H=hockey, and M=modified traditional) and impact location (high or low and center or lateral) effects were examined via 3x2x2 ANOVA. For Study2, design and ball trajectory effects were analyzed via 3x2 ANOVA. In Study1, the triple interaction was significant. For high/center collisions, T & H were 41% lower than M; for low/center impacts, H was 40% less than T & M; for high/side strikes, H was 33% less than T which was 32% less than M; and all 3 designs were equivalent for low/side contacts. T and H utilized different protection schemes. For T, energy transfer was reduced when equipment was displaced. For H, the more angled mask deflected the ball’s energy. Both mechanisms were impaired for M. In Study2, no significant effects were identified. The trajectory conditions may have relied solely on the mask padding. Both the T and H designs offer protection, with the H performing somewhat better for the conditions tested here

Screening for Gynecologic Conditions With Pelvic Examination US Preventive Services Task Force Recommendation Statement

IMPORTANCE Many conditions that can affect women\u27s health are often evaluated through pelvic examination. Although the pelvic examination is a common part of the physical examination, it is unclear whether performing screening pelvic examinations in asymptomatic women has a significant effect on disease morbidity and mortality. OBJECTIVE To issue a new US Preventive Services Task Force(USPSTF) recommendation on screening for gynecologic conditions with pelvic examination for conditions other than cervical cancer, gonorrhea, and chlamydia, for which the USPSTF has already made specific recommendations. EVIDENCE REVIEW The USPSTF reviewed the evidence on the accuracy, benefits, and potential harms of performing screening pelvic examinations in asymptomatic, nonpregnant adult women 18 years and older who are not at increased risk for any specific gynecologic condition. FINDINGS Overall, the USPSTF found inadequate evidence on screening pelvic examinations for the early detection and treatment of a range of gynecologic conditions in asymptomatic, nonpregnant adult women. CONCLUSIONS AND RECOMMENDATION The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of performing screening pelvic examinations in asymptomatic, nonpregnant adult women. (I statement) This statement does not apply to specific disorders for which the USPSTF already recommends screening (ie, screening for cervical cancer with a Papanicolaou smear, screening for gonorrhea and chlamydia)