Pre-Processing Power Traces to Defeat Random Clocking Countermeasures

We describe a pre-processing correlation attack on an FPGA implementation of AES, protected with a random clocking countermeasure that exhibits complex variations in both the location and amplitude of the power consumption patterns of the AES rounds. It is demonstrated that the merged round patterns can be pre-processed to identify and extract the individual round amplitudes, enabling a successful power analysis attack. We show that the requirement of the random clocking countermeasure to provide a varying execution time between processing rounds can be exploited to select a sub-set of data where sufficient current decay has occurred, further improving the attack. In comparison with the countermeasure's estimated security of 3 million traces from an integration attack, we show that through application of our proposed techniques that the countermeasure can now be broken with as few as 13k traces.

Narrative of the suffering and defeat, of the North-Western Army under General Winchester : massacre of the prisoners, sixteen months imprisonment of the writer and others with the Indians and British

Printed by A.G. Hodges

Coping with defeat : acute glucocorticoid and forebrain responses to social defeat vary with defeat episode behaviour

Individuals vary in the way in which they cope with stressful situations. It has been suggested that ‘active’ coping behaviour, characterised by aggression and territorial control, is more effective in moderating the stress associated with social defeat than ‘passive’ coping behaviour, as characterised by immobility, decreased reactivity, and low aggression. We used the rodent ‘resident/intruder’ paradigm to determine whether individual differences in coping behaviour modulate the acute adrenocortical response to social defeat. During the 10 min conflict episode, behaviours displayed by the intruder were recorded and subsequently scored. Intruders that engaged in large numbers of fights and/or frequently used physical structures to block the resident's approach (a behaviour referred to as ‘guarding’), displayed smaller corticosterone responses to defeat than other intruders. Corticosterone responses to defeat were unrelated to a measure of coping style preferences (defensive burying test) obtained prior to the defeat encounter. We further chose to investigate the neurobiological basis of this observation by comparing the patterns of defeat-induced neuronal activation in the forebrains of intruders that displayed high versus low numbers of defensive behaviours during the defeat episode. The results of this analysis indicated that ‘low fight’ and ‘low guard’ intruders, i.e. those that achieved a fight or a guard score below the 20th percentile, had significantly higher numbers of Fos-positive neurons in forebrain regions such as the medial prefrontal cortex and the amygdala than did control animals exposed to an empty resident's cage. In summary, the present data suggest that ‘active’ coping behaviour is associated with both a smaller adrenocortical response and a lower level of ‘neural activation’ following social defeat. This outcome differs from that of earlier studies, a difference that we suggest is due to the fact that the present study is the first to assess coping on the basis of behaviour actually displayed during the conflict interaction.

The effect of social defeat on tyrosine hydroxylase phosphorylation in the rat brain and adrenal gland

Tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, is regulated acutely by protein phosphorylation and chronically by protein synthesis. No studies have systematically investigated the phosphorylation of these sites in vivo in response to stressors. We specifically investigated the phosphorylation of TH occurring within the first 24 h in response to the social defeat stress in the rat adrenal, the locus coeruleus, substantia nigra and ventral tegmental area. Five groups were investigated; home cage control (HCC), two groups that underwent social defeat (SD+) which were sacrificed either 10 min or 24 h after the end of the protocol and two groups that were put into the cage without the resident being present (SD−) which were sacrificed at time points identical to the SD+. We found at 10 min there were significant increases in serine 40 and 31 phosphorylation levels in the locus coeruleus in SD+ compared to HCC and increases in serine 40 phosphorylation levels in the substantia nigra in SD+ compared to SD−. We found at 24 h there were significant increases in serine 19 phosphorylation levels in the ventral tegmental area in SD+ compared to HCC and decreases in serine 40 phosphorylation levels in the adrenal in SD+ compared to SD−. These findings suggest that the regulation of TH phosphorylation in different catecholamine-producing cells varies considerably and is dependent on both the nature of the stressor and the time at which the response is analysed.

Repeated social defeat selectively increases ΔFosB expression and histone H3 acetylation in the infralimbic medial prefrontal cortex

Exposure to social stress has been linked to the development and maintenance of mood-related psychopathology; however, the underlying neurobiological changes remain uncertain. In this study, we examined numbers of ΔFosB-immunoreactive cells in the forebrains of rats subjected to 12 episodes of social defeat. This was achieved using the social conflict model whereby animals are introduced into the home cage of older males (“residents”) trained to attack and defeat all such “intruders”; importantly, controls were treated identically except that the resident was absent. Our results indicated that the only region in which ΔFosB-positive cells were found in significantly higher numbers in intruders than in controls was the infralimbic medial prefrontal cortex (mPFC). This same effect was not apparent using another psychological stressor, noise stress. Cells of the infralimbic mPFC also displayed evidence of chromatin remodeling. We found that exposure to repeated episodes of social defeat increased numbers of cells immunoreactive for histone H3 acetylation, but not for histone H3 phosphoacetylation, in the infralimbic mPFC. Collectively, these findings highlight the importance of the infralimbic mPFC in responding to social stress—a finding that provides insight into the possible neurobiological alterations associated with stress-induced psychiatric illness.

Social defeat stress in rats: escalation of cocaine and speedball binge self-administration, but not heroin

Exposure to intermittent episodes of social defeat stress can increase drug seeking and leads to intense drug taking in rats.This study investigated the consequences of repeated, intermittent social defeat stress on patterns of drug self-administration in rats with access to heroin, cocaine, or a heroin-cocaine combination (speedball).Male Long-Evans rats were either handled (controls) or subjected to 25-min social defeat stress episodes on days 1, 4, 7, and 10 during confrontations with an aggressive resident. Ten days following the last defeat, rats were assessed for locomotor cross-sensitization in response to heroin or cocaine. Animals were then prepared with intrajugular catheters for drug self-administration. Separate groups of controls and defeated rats were examined for self-administration of heroin (experiment 1), a heroin-cocaine combination (experiment 2), or cocaine (experiment 3). Drug self-administration patterns were evaluated using fixed or progressive ratio schedules of reinforcement during limited access sessions or a 24-h unlimited access binge.Rats with a history of intermittent social defeat stress showed sensitized locomotor behavior when challenged with heroin or cocaine relative to controls. During the 24-h binge session, defeated rats escalated cocaine-taking behavior (ca. 110 mg/kg vs. 66 mg/kg in controls), persisted in self-administering cocaine or the heroin-cocaine mixture for more hours, and showed a tendency for increased heroin-cocaine intake, but no effects on heroin taking.A history of social defeat stress seems to preferentially promote escalated intake of cocaine but not heroin, unless a heroin-cocaine combination is available.