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# Security Analysis of Safe and Seldonian Reinforcement Learning Algorithms

NIPS 2020, (2020)

EI

摘要

We analyze the extent to which existing methods rely on accurate training data for a specific class of reinforcement learning (RL) algorithms, known as Safe and Seldonian RL. We introduce a new measure of security to quantify the susceptibility to perturbations in training data by creating an attacker model that represents a worst-case an...更多

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简介

- Reinforcement learning (RL) algorithms have been proposed for many high-risk applications, such as improving type 1 diabetes and sepsis treatments [44; 18].
- The safety test first computes estimates of the expected performance of a new policy from training data, using importance sampling (IS).
- The authors propose a new algorithm that is more robust to anomalies in training data, ensuring safety with high probability when an upper bound on the number of adversarially corrupt data points is known.

重点内容

- Reinforcement learning (RL) algorithms have been proposed for many high-risk applications, such as improving type 1 diabetes and sepsis treatments [44; 18]
- We focus on a worst-case setting, where an attacker modifies training data to maximize the probability that the Seldonian RL algorithm returns an unsafe policy
- In Corollary 1, we show that when k is chosen correctly, our algorithm meets a user-specified level of security against an attacker, whose optimal strategy does not change even if they know we are using Panacea
- When viewed as an Markov decision process (MDP), actions correspond to directions the agent can move, and states correspond to its current location on the grid
- Our results show that corrupting D collected from adult#003 within type 1 diabetes Mellitus simulator (T1DMS) can cause a Seldonian RL algorithm to select a bad policy, i.e., a new distribution over policies with lower return than πb
- We evaluated the number of trajectories that must to be added to D before φ incorrectly returns unsafe policies with probability more than δ

结果

- The authors focus on a worst-case setting, where an attacker modifies training data to maximize the probability that the Seldonian RL algorithm returns an unsafe policy.
- For a given k, the optimal attack is to create a trajectory that maximizes the value of the IS weight and return.
- The authors describe the algorithm Panacea, named after the Greek goddess of healing, that provides α-security, with a user-specified α, if the number of corrupt trajectories in D is upper bounded.
- In Corollary 1, the authors show that when k is chosen correctly, the algorithm meets a user-specified level of security against an attacker, whose optimal strategy does not change even if they know the authors are using Panacea.
- Let k denote the number of adversarial trajectories added by the attacker, and k denote the input provided to Panacea by the user.
- When this value is upper bounded correctly, k = k, and Panacea computes a clipping weight for the given estimator, denoted by c∗, , using Table 1.
- If the number of adversarial trajectories in D is upper bounded, rewriting (6) in terms of c∗, , and solving (6) for a clean expression for c∗, by substituting α , k and L∗, with the user-specified inputs, equals the clipping weights found in Table 1 for different estimators.

结论

- Instead of finding a trajectory with the largest IS weight and return, the optimal attack strategy is selecting a CR and CF such that the ratio of their joint probability under πe to that of πb is maximized, i.e., arg maxCR ∈[5,50] arg maxCF ∈[1,31] πe(CR , CF , θ3, θ4)/πb(CR , CF , θ1, θ2).
- For Panacea, the authors computed the clipping weights, found in Table 1 per estimator, using the userspecified α and the actual number of adversarial trajectories added by the attacker.
- When creating safe AI algorithms that can directly impact people’s lives, the authors should ensure performance guarantees with high probability, and the development of metrics that evaluate the “quality” of training data, which often reflect systemic biases and human error.

- Table1: α–security of current methods (center); settings for clipping weight, c, for α-security written in terms of a user-specified k and α (right). The minimum IS weight is denoted by imin. By Theorem 1, the security of Panacea is

相关工作

- Our paper arguably falls into the broad body of work aimed at creating algorithms that can withstand uncertainty introduced at any stage of the RL framework. Some works view a component as an adversary with stochastic behavior. For an overview of risk-averse methods, e.g., those that incorporate stochasticity into the system, refer to the work of Garcia and Fernandez [7].

Other works incorporate an adversary to model worst-case scenarios. In a model-free setting, Morimoto and Doya [32] introduced Robust RL that models the environment as an adversary to address parameter uncertainty in MDPs. Pinto et al [37] extend this work to non-linear policies that are represented as neural networks. Lim et al [23] consider MDPs with some adversarial state-action pairs. In model-based settings, i.e., those that build an explicit model of the system, although an adversary is not present, worst-case analyses assume different components of an MDP are unknown [34; 46; 39]. Using the definition of safety we have introduced, Ghavamzadeh et al [8] and Laroche et al [22] created algorithms for learning safe policies in a model-based setting. Although we are also interested in ensuring security for these approaches, we focus on a model-free setting that requires a different set of assumptions and attacker model.

基金

- This work was supported in part by NSF Award #2018372 and a gift from Adobe
- Research reported in this paper was also sponsored in part by the CCDC Army Research Laboratory under Cooperative Agreement W911NF-17-2-0196 (ARL IoBT CRA)

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