Checksum validation is the process of verifying the integrity of a mobile app to ensure that it has not been tampered with or modified in any way. The purpose of checksum validation is to protect mobile app users from malicious software and other security threats.
A checksum is a simple cryptographic value calculated from a block of data that can be used to verify the integrity and authenticity of that data. For example a checksum value calculated over image data can be used to verify the image has not been altered when transferred over the internet.
Checksums values are generated utilizing well known algorithms that produce unique non-overlapping values based on small changes to the input data. The most common algorithms used to calculate checksums include cyclic redundancy check (CRC), message digest (MD), and secure hash algorithms (SHA). These algorithms are designed to produce a unique checksum value for each set of data, making it difficult for someone to generate a false checksum value. For example, the MD5 algorithm creates a 128-bit hash value that is unique to the input data. SHA-256, which is another popular algorithm, creates a 256-bit hash value.
A checksum algorithm works by taking the data that needs to be checked and processing it through a set of operations to generate the checksum value. Checksum algorithms use a combination of operations such as addition, subtraction, and bitwise XOR to transform the data into a unique fixed-length value.
Checksums provide a fast and simple way to identify data corruption, verify integrity, and validate authenticity of data through cryptographic hash comparisons. Checksums are valuable for the following key reasons.
A mobile app can be configured perform checksum verification on itself by using a checksum algorithm to compute the checksum of the app's executable code and comparing it to a pre-computed checksum value, which would have been computed using the same algorithm when the app was created. If the two codes match, it means that the data has not been modified. If the checksums do not match, it indicates that the data has been altered.
Enabling a mobile app to perform checksum validation should be part of a Mobile RASP (Runtime Application Self-Protection) solution.
The following process outlines the steps that could be used to perform checksum verification in a mobile app.
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