README.md
1# apksig
2
3apksig is a project which aims to simplify APK signing and checking whether APK signatures are
4expected to verify on Android. apksig supports
5[JAR signing](https://docs.oracle.com/javase/8/docs/technotes/guides/jar/jar.html#Signed_JAR_File)
6(used by Android since day one) and
7[APK Signature Scheme v2](https://source.android.com/security/apksigning/v2.html) (supported since
8Android Nougat, API Level 24). apksig is meant to be used outside of Android devices.
9
10The key feature of apksig is that it knows about differences in APK signature verification logic
11between different versions of the Android platform. apksig thus thoroughly checks whether an APK's
12signature is expected to verify on all Android platform versions supported by the APK. When signing
13an APK, apksig chooses the most appropriate cryptographic algorithms based on the Android platform
14versions supported by the APK being signed.
15
16The project consists of two subprojects:
17
18 * apksig -- a pure Java library, and
19 * apksigner -- a pure Java command-line tool based on the apksig library.
20
21
22## apksig library
23
24apksig library offers three primitives:
25
26 * `ApkSigner` which signs the provided APK so that it verifies on all Android platform versions
27 supported by the APK. The range of platform versions can be customized.
28 * `ApkVerifier` which checks whether the provided APK is expected to verify on all Android
29 platform versions supported by the APK. The range of platform versions can be customized.
30 * `(Default)ApkSignerEngine` which abstracts away signing APKs from parsing and building APKs.
31 This is useful in optimized APK building pipelines, such as in Android Plugin for Gradle,
32 which need to perform signing while building an APK, instead of after. For simpler use cases
33 where the APK to be signed is available upfront, the `ApkSigner` above is easier to use.
34
35_NOTE: Some public classes of the library are in packages having the word "internal" in their name.
36These are not public API of the library. Do not use \*.internal.\* classes directly because these
37classes may change any time without regard to existing clients outside of `apksig` and `apksigner`._
38
39
40## apksigner command-line tool
41
42apksigner command-line tool offers two operations:
43
44 * sign the provided APK so that it verifies on all Android platforms supported by the APK. Run
45 `apksigner sign` for usage information.
46 * check whether the provided APK's signatures are expected to verify on all Android platforms
47 supported by the APK. Run `apksigner verify` for usage information.
48
49The tool determines the range of Android platform versions (API Levels) supported by the APK by
50inspecting the APK's AndroidManifest.xml. This behavior can be overridden by specifying the range
51of platform versions on the command-line.
52