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Proofreading fixes part 2 0x05a #2292

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Oct 20, 2022
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Proofreading fixes part 2 0x05a #2292

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Proofreading fixes 0x05a-Platform-Overview.md
Laancelot Oct 20, 2022
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Update Document/0x05a-Platform-Overview.md
cpholguera Oct 20, 2022
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16 changes: 8 additions & 8 deletions Document/0x05a-Platform-Overview.md
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Expand Up @@ -660,17 +660,17 @@ It is no longer possible to sign APKs independently, because the proof-of-rotati

#### APK Signature Scheme (v4 Scheme)

The APK Signature Scheme v4 was introduced along with Android 11 (API level 30). which requires all devices launched with it to have [fs-verity](https://kernel.org/doc/html/latest/filesystems/fsverity.html) enabled by default. fs-verity is a Linux kernel feature that is primarily used for file authentication (detection of malicious modifications) due to its extremely efficient file hash calculation. Read requests only will succeed if the content verifies against trusted digital certificates that were loaded to the kernel keyring during boot time.
The APK Signature Scheme v4 was introduced along with Android 11 (API level 30) and requires all devices launched with Android 11 and up to have [fs-verity](https://www.kernel.org/doc/html/latest/filesystems/fsverity.html) enabled by default. fs-verity is a Linux kernel feature that is primarily used for file authentication (detection of malicious modifications) due to its extremely efficient file hash calculation. Read requests only will succeed if the content verifies against trusted digital certificates that were loaded to the kernel keyring during boot time.

The v4 signature requires a complementary v2 or v3 signature and in contrast to previous signature schemes, the v4 signature is stored in a separate file `<apk name>.apk.idsig`. Remember to specify it using the `--v4-signature-file` flag when verifying a v4-signed APK with `apksigner verify`.

You can find more detailed information in the [Android developer documentation](https://source.android.com/security/apksigning/v4).

#### Creating Your Certificate

Android uses public/private certificates to sign Android apps (.apk files). Certificates are bundles of information; in terms of security, keys are the most important type of this information Public certificates contain users' public keys, and private certificates contain users' private keys. Public and private certificates are linked. Certificates are unique and can't be re-generated. Note that if a certificate is lost, it cannot be recovered, so updating any apps signed with that certificate becomes impossible.
Android uses public/private certificates to sign Android apps (.apk files). Certificates are bundles of information; in terms of security, keys are the most important part of that bundle. Public certificates contain users' public keys, and private certificates contain users' private keys. Public and private certificates are linked. Certificates are unique and can't be re-generated. Note that if a certificate is lost, it cannot be recovered, so updating any apps signed with that certificate becomes impossible.
App creators can either reuse an existing private/public key pair that is in an available KeyStore or generate a new pair.
In the Android SDK, a new key pair is generated with the `keytool` command. The following command creates a RSA key pair with a key length of 2048 bits and an expiry time of 7300 days = 20 years. The generated key pair is stored in the file 'myKeyStore.jks', which is in the current directory):
In the Android SDK, a new key pair is generated with the `keytool` command. The following command creates a RSA key pair with a key length of 2048 bits and an expiry time of 7300 days = 20 years. The generated key pair is stored in the file 'myKeyStore.jks', which is in the current directory:

```bash
keytool -genkey -alias myDomain -keyalg RSA -keysize 2048 -validity 7300 -keystore myKeyStore.jks -storepass myStrongPassword
Expand All @@ -694,7 +694,7 @@ In this example, an unsigned app ('myUnsignedApp.apk') will be signed with a pri

##### Zipalign

The `zipalign` tool should always be used to align the APK file before distribution. This tool aligns all uncompressed data (such as images, raw files, and 4-byte boundaries) within the APK that helps improve memory management during app runtime.
The `zipalign` tool should always be used to align the APK file before distribution. This tool aligns all uncompressed data (such as images, raw files, and 4-byte boundaries) within the APK, which helps improve memory management during app runtime.

> Zipalign must be used before the APK file is signed with apksigner.

Expand All @@ -706,15 +706,15 @@ Apps can be installed on an Android device from a variety of sources: locally vi

Whereas other vendors may review and approve apps before they are actually published, Google will simply scan for known malware signatures; this minimizes the time between the beginning of the publishing process and public app availability.

Publishing an app is quite straightforward; the main operation is making the signed APK file downloadable. On Google Play, publishing starts with account creation and is followed by app delivery through a dedicated interface. Details are available at [the official Android documentation](https://developer.android.com/distribute/googleplay/start.html "Review the checklists to plan your launch").
Publishing an app is quite straightforward; the main operation is making the signed APK file downloadable. On Google Play, publishing starts with account creation and is followed by app delivery through a dedicated interface. Details are available at [the official Android documentation](https://play.google.com/console/about/guides/releasewithconfidence/ "Review the checklists to plan your launch").

## Android Application Attack Surface

The Android application attack surface consists of all components of the application, including the supportive material necessary to release the app and to support its functioning. The Android application may be vulnerable to attack if it does not:

- Validate all input by means of IPC communication or URL schemes, see also:
- [Testing for Sensitive Functionality Exposure Through IPC](0x05h-Testing-Platform-Interaction.md#testing-for-sensitive-functionality-exposure-through-ipc-mstg-platform-4)
- [Testing Custom URL Schemes](0x05h-Testing-Platform-Interaction.md#testing-custom-url-schemes-mstg-platform-3)
- [Testing Custom URL Schemes](0x05h-Testing-Platform-Interaction.md#testing-deep-links-mstg-platform-3)
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- Validate all input by the user in input fields.
- Validate the content loaded inside a WebView, see also:
- [Testing JavaScript Execution in WebViews](0x05h-Testing-Platform-Interaction.md#testing-javascript-execution-in-webviews-mstg-platform-5)
Expand All @@ -724,6 +724,6 @@ The Android application attack surface consists of all components of the applica
- [Testing Network Communication](0x04f-Testing-Network-Communication.md#testing-network-communication)
- [Android Network Communication](0x05g-Testing-Network-Communication.md)
- Securely stores all local data, or loads untrusted data from storage, see also:
- [Data Storage on Android](0x05d-Testing-Data-Storage.md#data-storage-on-android)
- [Data Storage on Android](0x05d-Testing-Data-Storage.md)
- Protect itself against compromised environments, repackaging or other local attacks, see also:
- [Android Anti-Reversing Defenses](0x05j-Testing-Resiliency-Against-Reverse-Engineering.md#android-anti-reversing-defenses)
- [Android Anti-Reversing Defenses](0x05j-Testing-Resiliency-Against-Reverse-Engineering.md)