Modeling Resources in Permissionless Longest-chain Total-order Broadcast

Blockchain protocols implement total-order broadcast in a permissionless setting, where processes can freely join and leave. In such a setting, to safeguard against Sybil attacks, correct processes rely on cryptographic proofs tied to a particular type of resource to make them eligible to order transactions. For example, in the case of Proof-of-Work (PoW), this resource is computation, and the proof is a solution to a computationally hard puzzle. Conversely, in Proof-of-Stake (PoS), the resource corresponds to the number of coins that every process in the system owns, and a secure lottery selects a process for participation proportionally to its coin holdings. Although many resource-based blockchain protocols are formally proven secure in the literature, the existing security proofs fail to demonstrate why particular types of resources cause the blockchain protocols to be vulnerable to distinct classes of attacks. For instance, PoS systems are more vulnerable to long-range attacks, where an adversary corrupts past processes to re-write the history, than Proof-of-Work and Proof-of-Storage systems. Proof-of-Storage-based and Proof-of-Stake-based protocols are both more susceptible to private double-spending attacks than Proof-of-Work-based protocols; in this case, an adversary mines its chain in secret without sharing its blocks with the rest of the processes until the end of the attack. In this paper, we formally characterize the properties of resources through an abstraction called resource allocator and give a framework for understanding longest-chain consensus protocols based on different underlying resources. In addition, we use this resource allocator to demonstrate security trade-offs between various resources focusing on well-known attacks (e.g., the long-range attack and nothing-at-stake attacks)

Modeling Resources in Permissionless Longest-Chain Total-Order Broadcast

Blockchain protocols implement total-order broadcast in a permissionless setting, where processes can freely join and leave. In such a setting, to safeguard against Sybil attacks, correct processes rely on cryptographic proofs tied to a particular type of resource to make them eligible to order transactions. For example, in the case of Proof-of-Work (PoW), this resource is computation, and the proof is a solution to a computationally hard puzzle. Conversely, in Proof-of-Stake (PoS), the resource corresponds to the number of coins that every process in the system owns, and a secure lottery selects a process for participation proportionally to its coin holdings. Although many resource-based blockchain protocols are formally proven secure in the literature, the existing security proofs fail to demonstrate why particular types of resources cause the blockchain protocols to be vulnerable to distinct classes of attacks. For instance, PoS systems are more vulnerable to long-range attacks, where an adversary corrupts past processes to re-write the history, than PoW and Proof-of-Storage systems. Proof-of-Storage-based and PoS-based protocols are both more susceptible to private double-spending attacks than PoW-based protocols; in this case, an adversary mines its chain in secret without sharing its blocks with the rest of the processes until the end of the attack. In this paper, we formally characterize the properties of resources through an abstraction called resource allocator and give a framework for understanding longest-chain consensus protocols based on different underlying resources. In addition, we use this resource allocator to demonstrate security trade-offs between various resources focusing on well-known attacks (e.g., the long-range attack and nothing-at-stake attacks)

Long-term follow-up free of ventricular fibrillation recurrence after resuscitated cardiac arrest in a myotonic dystrophy type 1 patient

Cardiac involvement in myotonic dystrophy type 1 (DM1) is frequent with increased incidence of conduction disturbances and sudden cardiac death when compared with general population. We describe a 38-year-old man in whom the diagnosis of DM1 was made 8 years after occurrence of cardiac arrest owing to ventricular fibrillation and discuss management of DM1 patients at risk for sudden cardiac death

Restrictive respiratory sindrome in DM2 patients

Objectives: Respiratory involvement in myotonic dystrophy type 1 (DM1) is frequent. Respiratory insufficiency is, together with cardiac failure, the main cause of death in these patients. Reports on respiratory involvement in DM2 are limited. The aims of our study were to determine the frequency and severity of respiratory involvement and sleep apnoea in patients with DM2 compared to DM1. Methods: 20 patients with genetically determined DM2 (mean age 64.3 \ub1 8) and 40 patients with moderately severe age-matched DM1 (mean age 38.5 \ub1 11) were subjected to muscle strength assessment and: (1) subjective assessment of excessive daytime sleepiness (Epworth Sleepiness Scale-ESS); (2) spirometry and nocturnal polygraphy (PSG). Results: (1) 4 of 20 (20%) patients with DM2 and 12 of 40 (30%) patients with DM1 complained of daytime sleepiness; (2) 5 of 20 (25%) patients with DM2 and 14 patients with DM1 (35%) showed a restrictive respiratory impairment on respiratory function tests. Indication to nocturnal assisted ventilation (Bi-level) either due to nocturnal desaturation or sleep apnoeas was identified in 30% patients with DM1 subjected to PSG compared to 10% of patients with DM2 subjected to PSG. Conclusions: Although preliminary, our results indicate that respiratory involvement in DM2 is present and needs to be considered in patients with DM2 just like in DM1, because of the potentially treatable nature of the associated symptoms. Whether severity of respiratory involvement correlates with muscle impairment (MMRC) and disease duration needs to be further explored on a larger number of patients

Tolerability and safety of mexiletine in patients with myotonia dystrophy type 1 over time

Objectives: Although mexiletine is accepted as an antimyotonic agent in the non-dystrophic myotonias, there is still no general consensus S128 123 regarding safety in the dystrophic myotonias. In this study our primary aim was to assess tolerability and safety in patients with myotonic dystrophy type 1 (DM 1) over time. In addition our secondary aims were to determine of the effects of the drug on myotonia and muscle strength in these same patients. Methods: 36 patients with moderately-severe adult DM1 were treated with mexiletine 200 mg tid and compared to age-, diseaseduration and MRC- matched 34 untreated patients with moderatelysevere DM1. Manual muscle strength (MRC), myotonia self-assessment scales (0\u20135 scale) and cardiac parameters (PR interval; QRS duration,QRSD; heart rate, HR;ejection fraction, EF) were determined before and after long-term mexiletine treatment (DM1: mean treatment duration 7.5 years \ub1 3.7; DM2: 5.2 \ub1 3.5 years). All patients filled in a form of reporting on tolerability and side-effects of treatment. In a subgroup of patients fulfilling criteria for electrophysiological study. Results: Preliminary data suggest that initial and final PR, QRSD, HR, EF were similar in the treated and untreated DM1 groups. Sideeffects were minimal. Myotonia improved significantly in the treated DM1 compared to the untreated patients (p[0.0001).MRC decreased significantly in both treated and untreated DM1 patients Conclusion: Although preliminary, our data suggest that mexiletine is safe and well-tolerated in DM1 patients. There are indications that myotonia but not muscle strength may improve with prolonged treatment. To further confirm or refute our data, we are extending the study to a larger group of patients. In addition, the effects of intravenous mexiletine on the main electrophysiological functional parameters and on the arrhytmia inducibility will also be determined