The robustness principle postulates that when accepting input, you should be liberal in what you accept. In cyber security, and in particular in crypt

Abusing insecure defaults: Forging ciphertexts under Galois Counter Mode for the Node.js crypto module

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2024-04-18 13:30:09

The robustness principle postulates that when accepting input, you should be liberal in what you accept. In cyber security, and in particular in cryptography, the opposite is true. This blog post will cover one such instance, where an insecure default renders the Node.js crypto API prone to misuse: I will showcase how the permissibility of different authentication tag lengths in the Galois Counter Mode (GCM) NIST specification interacts with the unopinionated Decipher class of Node and, if used in its default configuration, allows an attacker to brute-force authentication tags or even key material, leading to loss of authenticity. Multiple high-profile organizations and popular open-source repositories were affected by implementation flaws stemming from the permissive APIs, both in standards and software.

Galois Counter Mode is a block cipher mode of operation that offers authenticated encryption, meaning the output of an encryption is not just the usual ciphertext but also an authentication tag that is used to check the integrity (whether the ciphertext has been tampered with).