Premium Essay


In: Computers and Technology

Submitted By cantuz
Words 1827
Pages 8
Homework 5
4.2 Consider a "CCA-type" extension of the definition of secure message authentication codes where the adversary is provided with both a Mac and Vrfy oracle. (a) Provide a formal definition and explain why such a notion may make sense. (b) Show that when the Mac scheme is deterministic, your definition is equivalent to Definition 4.2. (c) Show that when the Mac scheme may be probabilistic, the definitions are not equivalent. (That is, show that there exists a probabilistic scheme that is secure by Definition 4.2 but not by your definition.) Consideration The message authentication experiment Mac-forge, Π(n):

1. A random key k ← {0, 1}n is chosen. 2. The adversary is given oracle access to Mack (·) and Vrfyk (·, ·) and outputs a pair (m , t ). Formally, (m , t ) ← Mack (·), Vrfyk (·,·) (1n ). Let Q denote the queries asked by during the execution. 3. The output of the experiment is defined to be 1 iff m ∈ Q and Vrfyk (m , t ) = 1. A message authentication code Π = (Gen, Mac, Vrfy) is existentially unforgeable under an adaptive chosen-message attack, or just secure, if for all probablistic polynomial-time adversaries , there exists a negligible function negl such that: Pr Mac-forge
,Π (n) = 1

≤ negl (n)

Access to Vrfyk (·, ·) may not be beneficial to the adversary . Let’s say the adversary somehow manages to generate a pair (m , t ) and attempts to query its Vrfy oracle to check its validity. This seems completely plausible but the adversary has to take wild guesses in exponentially many tag candidates, of which the probability of success is negligible. Also, the Vrfy oracle returns merely a single bit, so the adversary is unable to obtain any practical information on the scheme by querying its Vrfy oracle. Say, the Mac scheme is deterministic. There exists one unique tag corresponding to any specific message. Once the adversary obtains sufficient…...

Similar Documents

Free Essay


...aspe ans glos panno rula Asc ozo Le sum rum Thenus wo otia luviride bric lebo olh a lu Cytt s steopensis rcore Phy a llacti ria darw us Neo Blum nia g inii Amy b u loca ulgaria eria gra ttata Scle rpus e premn minis rotin ncep ophila Monia scle haloid ilinia rotio es ru Rhy Monilifructico m nia la la tis xa Cu ma sa Spa donia clicinum Lulwthulari onfusa a o Oph Magna rthia fuflavida Pse iocera porthe cicola udoh s lep to grise a Oph lonectr sporu a Oph iostom ia falca m iosto a pic ta m eae Oph P iosto esotum a bicolor ma frag Oph penicilla rans S io Oph porothri stoma tum iosto x sch ulmi m Op Ophio a sten enckii Ophiohiostomstoma oceras a cu aino sto Leuc ma euro cullatu ae ostom phio m a pers ides Cry En o Cryp phonecdothia gy onii tria ho ro Cry nectria cuben sa Cryp phonec havane sis Asco hone tria ra nsis vagin ctria d pa icalis o Cam spora sterasitica a Chaerops mic llipala tomiu rospo m ela ra So Ne rdaria fim tum Podourospora icola cr sp Melio ora anseassa la rin Melio niesslean a Kiono la jud a ch Kiono aeta ra diana chae mifera Kiono chae ta spissa Obola ta ivori rina d ensis Ro ry Xylasellinia ne ophila ria po lym catrix HypXylaria ca orpha oxylo rp n frag ophila Vertic iform ill Hypom Glomerelium dah e yces ch la cing liae ulat ry Hyp sosperm a Chaet ocrea luteus Nec opsina fu a Nectrtria aureof lva Mycoa ia ochrol ulva eu ra Spi chis inve ca Geosm cellum rose rsa um ithia Hamilt Geosmith lavendul on ia a Cordy aphis styr putterillii cepi aci sy Paecilo oideus......

Words: 13456 - Pages: 54

Free Essay

Medical Surgical Nursing or blond hair, fair skin, and blue eyes). NOTE Skin cancer is the most common form of cancer in the United States. CAUTION Remember the alphabet A B C D when assessing skin lesions. If the answer is yes to any of the questions listed here, it could indicate a possible malignant lesion: . A—Is the lesion asymmetrical in shape? . B—Are the borders of the lesion irregular? . C—Are there different colors within the lesion? . D—Is the diameter of the lesion more than 5mm? . Stomach—Risk factors include a diet high in smoked foods and lacking in fruits and vegetables, gastric ulcers, Helicobacter pylori bacteria, heredity, pernicious anemia, and chronic gastritis. . Testes—Risk factors include infections, genetic or endocrine factors, and cryp- torchidism. 10_078973706x_ch09.qxd 1/14/08 2:12 PM Page 137 137 Management of the Client with Cancer Cancer Prevention An early diagnosis can mean a better cure rate for a patient with cancer. Certain cancers can even be prevented by interventions. The nurse can make a substantial impact by the use of education in preventive teaching and early detection techniques. One way the incidence of cancer can be decreased is by a change in eating habits. For example, with colon cancer the risk is decreased by the avoidance of fatty, fried foods and increasing the intake of fruits, vegetables, and whole grains. Another way to decrease incidence is by staying away from carcinogens such as smoking, alcohol, and toxins. It is important......

Words: 177674 - Pages: 711

Premium Essay

As Good as It Gets

...friend, Gala, died. The two events sent him into a deep depression. He moved to Pubol, in a castle that he had purchased and remodeled for Gala, possibly to hide from the public or, as some speculate, to die. In 1984, Dalí was severely burned in a fire. Due to his injuries, he was confined to wheelchair. Friends, patrons and fellow artists rescued him from the castle and returned him to Figueres, making him comfortable at the Teatro-Museo. In November 1988, Salvador Dalí entered a hospital in Figueres with a failing heart. After a brief convalescence, he returned to the Teatro-Museo. On January 23, 1989, in the city of his birth, Dalí died of heart failure at the age of 84. His funeral was held at the Teatro-Museo, where he was buried in a cryp Od2...

Words: 2860 - Pages: 12