The signature is only relevant to ensure the authenticity of subsequent versions of an app or to identify related apps.) Any developer can create his or her own certificate to sign applications. (Note that Android is based on the principle of self-signing. At the time, Android relied entirely on the original JAR signature scheme to ensure the authenticity of the app. It adds more standardized structure with files like x for Dalvik bytecode and resources.arsc for resources. When Android came along, its APK format for distributing apps in turn built on the JAR format. A file like META-INF/CERT.SF contains further derived hashes and a file like META-INF/CERT.RSA contains the signing certificate and the actual cryptographic signature for the hashes. It is also the basis of the JAR signature scheme: it contains a cryptographic hash for each of the files in the archive. The META-INF/MANIFEST.MF file contains some basic headers, for example with the application name and with version numbers. A JAR file is essentially a ZIP archive that includes additional metadata in the form of META-INF/* files. Sun used the ZIP format as the foundation for the JAR format it introduced in the 1990s for distributing Java code. It also enabled the storage of large (more than 720 KB!) files on multiple floppy disks (multi-ZIP). The format provided practical solutions for problems with compression, checksums and redundant headers. It combines individual files and some metadata in a single file for convenient transfer and archival. In the 1980s, Phil Katz created the ZIP format. A bit of history: from ZIP over JAR to APK We zoom in on the new APK signature scheme v3, putting it into context and discussing the new opportunities it offers. While updates in the user interface catch the most attention, some security improvements under the hood are just as interesting. Android 9.0 ("Pie") introduced a lot of new functionality.
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