Authors:
(1) Anna-Katharina Wickert, Technische Universität Darmstadt, Darmstadt, Germany (wickert@cs.tu-darmstadt.de);
(2) Lars Baumgärtner, Technische Universität Darmstadt, Darmstadt, Germany (baumgaertner@cs.tu-darmstadt.de);
(3) Florian Breitfelder, Technische Universität Darmstadt, Darmstadt, Germany (florian.breitfelder@tu-darmstadt.de);
(4) Mira Mezini, Technische Universität Darmstadt, Darmstadt, Germany (mezini@cs.tu-darmstadt.de). Table of Links Abstract and 1 Introduction 2 Background 3 Design and Implementation of Licma and 3.1 Design 3.2 Implementation 4 Methodology and 4.1 Searching and Downloading Python Apps 4.2 Comparison with Previous Studies 5 Evaluation and 5.1 GitHub Python Projects 5.2 MicroPython 6 Comparison with previous studies 7 Threats to Validity 8 Related Work 9 Conclusion, Acknowledgments, and References 2 BACKGROUND Crypto libraries enable developers to use crypto primitives, like symmetric key encryption or password-based encryption (PBE), in their application. However, studies have shown that developers struggle to use those APIs correctly and securely. For example, Krüger et al. [8] show that 95 % of the Android applications using crypto have at least one crypto misuse. In the remainder of the paper, we define a crypto misuse, in short misuse, as a usage of a crypto library which is a formally correct use of the API, e.g., not causing a crash, but is unsafe. In this paper, we focus on six commonly discussed crypto misuses [4, 13] which we will introduce next. For AES encryption, a block mode is used to combine several blocks for encryption and decryption. However, some block modes are considered insecure by experts. Rule 1 (§1) and rule 2 (§2) cover two insecure usages of block modes. §1 prohibits the usage of ECB which is deterministic and not secure. §2 focus on a nonrandom initialization vector (IV) for the block mode CBC. Due to the predictability of the IV, the usage of CBC is deterministic and not secure. Further, a key protects confidential information. Thus, rule 3 (§3) states that the key should be confidential and not a static one hard-coded in the source. For PBE, a salt and the number of iterations harden the password against dictionary attacks. Rule 4 (§4) highlights that a non-random salt reduces the security of the crypto primitive to using no salt, which is considered insecure. Rule 5 (§5) concentrates on the fact that several iterations are required to harden the crypto primitive against attacks. Thus, Egele et al. [4] suggest the minimum recommended value of 1,000 iterations as defined in the PBE standard PKCS#5. A seed can ensure that the output of a random number generator is non-deterministic. Rule 6 (§6) covers that static seeds lead to deterministic outputs. Common Java [4] and C/C++ [13] libraries expect a seed, while the analyzed Python APIs avoid this by design. This paper is available on arxiv under CC BY 4.0 DEED license. Authors: (1) Anna-Katharina Wickert, Technische Universität Darmstadt, Darmstadt, Germany (wickert@cs.tu-darmstadt.de); (2) Lars Baumgärtner, Technische Universität Darmstadt, Darmstadt, Germany (baumgaertner@cs.tu-darmstadt.de); (3) Florian Breitfelder, Technische Universität Darmstadt, Darmstadt, Germany (florian.breitfelder@tu-darmstadt.de); (4) Mira Mezini, Technische Universität Darmstadt, Darmstadt, Germany (mezini@cs.tu-darmstadt.de). Authors: Authors: (1) Anna-Katharina Wickert, Technische Universität Darmstadt, Darmstadt, Germany (wickert@cs.tu-darmstadt.de); (2) Lars Baumgärtner, Technische Universität Darmstadt, Darmstadt, Germany (baumgaertner@cs.tu-darmstadt.de); (3) Florian Breitfelder, Technische Universität Darmstadt, Darmstadt, Germany (florian.breitfelder@tu-darmstadt.de); (4) Mira Mezini, Technische Universität Darmstadt, Darmstadt, Germany (mezini@cs.tu-darmstadt.de). Table of Links Abstract and 1 Introduction Abstract and 1 Introduction 2 Background 2 Background 3 Design and Implementation of Licma and 3.1 Design 3 Design and Implementation of Licma and 3.1 Design 3.2 Implementation 3.2 Implementation 4 Methodology and 4.1 Searching and Downloading Python Apps 4 Methodology and 4.1 Searching and Downloading Python Apps 4.2 Comparison with Previous Studies 4.2 Comparison with Previous Studies 5 Evaluation and 5.1 GitHub Python Projects 5 Evaluation and 5.1 GitHub Python Projects 5.2 MicroPython 5.2 MicroPython 6 Comparison with previous studies 6 Comparison with previous studies 7 Threats to Validity 7 Threats to Validity 8 Related Work 8 Related Work 9 Conclusion, Acknowledgments, and References 9 Conclusion, Acknowledgments, and References 2 BACKGROUND Crypto libraries enable developers to use crypto primitives, like symmetric key encryption or password-based encryption (PBE), in their application. However, studies have shown that developers struggle to use those APIs correctly and securely. For example, Krüger et al. [8] show that 95 % of the Android applications using crypto have at least one crypto misuse. In the remainder of the paper, we define a crypto misuse, in short misuse, as a usage of a crypto library which is a formally correct use of the API, e.g., not causing a crash, but is unsafe. In this paper, we focus on six commonly discussed crypto misuses [4, 13] which we will introduce next. For AES encryption, a block mode is used to combine several blocks for encryption and decryption. However, some block modes are considered insecure by experts. Rule 1 (§1) and rule 2 (§2) cover two insecure usages of block modes. §1 prohibits the usage of ECB which is deterministic and not secure. §2 focus on a nonrandom initialization vector (IV) for the block mode CBC. Due to the predictability of the IV, the usage of CBC is deterministic and not secure. Further, a key protects confidential information. Thus, rule 3 (§3) states that the key should be confidential and not a static one hard-coded in the source. For PBE, a salt and the number of iterations harden the password against dictionary attacks. Rule 4 (§4) highlights that a non-random salt reduces the security of the crypto primitive to using no salt, which is considered insecure. Rule 5 (§5) concentrates on the fact that several iterations are required to harden the crypto primitive against attacks. Thus, Egele et al. [4] suggest the minimum recommended value of 1,000 iterations as defined in the PBE standard PKCS#5. A seed can ensure that the output of a random number generator is non-deterministic. Rule 6 (§6) covers that static seeds lead to deterministic outputs. Common Java [4] and C/C++ [13] libraries expect a seed, while the analyzed Python APIs avoid this by design. This paper is available on arxiv under CC BY 4.0 DEED license. This paper is available on arxiv under CC BY 4.0 DEED license. available on arxiv

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Addressing the Risks of Misusing Crypto Libraries

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