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smd:laboratoare:08 [2019/04/22 14:01] adriana.draghici [Task 2 - Signing configuration (3p)] |
smd:laboratoare:08 [2021/05/13 19:51] (current) adriana.draghici [Lab 8 - Cryptography 2] |
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| * Protect the app's APK using signing | * Protect the app's APK using signing | ||
| * Use Android's KeyStore to generate and store cryptographic keys and use them to sign an app | * Use Android's KeyStore to generate and store cryptographic keys and use them to sign an app | ||
| - | * Generate HMAC (hash-based message authentication code) to sign a message | + | * Verify message integrity using HMAC (hash-based message authentication code) |
| - | * Verify HMAC to check message integrity | + | * generate HMAC to sign a message |
| + | * verify HMAC to check that the received message was not modified | ||
| ===== Application signing ===== | ===== Application signing ===== | ||
| - | If you want to install an application on Android, the //apk// must be digitally signed with a certificate. For example, when you test your application on the emulator, Android Studio signs the apk with a debug certificate. The first time when you run or [[https://developer.android.com/studio/publish/app-signing#debug-mode|debug a project in Android Studio]], a debug keystore and certificate is automatically created using the Android SDK tools in **$HOME/.android/debug.keystore**. Also the keystore is initialized and the key password are set. | + | If you want to install an application on Android, the //apk// must be digitally signed with a certificate. For example, when you test your application on the emulator, Android Studio signs the apk with a debug certificate. The first time when you run or [[https://developer.android.com/studio/publish/app-signing#debug-mode|debug a project in Android Studio]], a debug keystore and certificate is automatically created using the Android SDK tools in **$HOME/.android/debug.keystore**. Also the keystore is initialized and the key password is set. |
| As a security measure the debug certificate needs to be used only for testing and for debug builds. This certificate is not secure for using on app stores. | As a security measure the debug certificate needs to be used only for testing and for debug builds. This certificate is not secure for using on app stores. | ||
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| Steps for generating and uploading key and keystore: | Steps for generating and uploading key and keystore: | ||
| - | - Go to **Build > Build > Generate Signed Bundle/APK** | + | - Go to **Build > Generate Signed Bundle/APK** |
| - | - Select **APK** | + | - Select **APK** |
| - | - Under Key store path choose **Create new** | + | - Under Key store path choose **Create new** |
| - | - Complete the fields and then continue with the signing steps below | + | - Complete the fields and then continue with the signing steps below |
| | | ||
| - | Sign app with key: | + | From here we continue to sign the app with the key stored in the newly created keystore. You can skip the first two steps if you are already in the window at the 3rd step: |
| - **Build -> Generate Signed Bundle/APK** | - **Build -> Generate Signed Bundle/APK** | ||
| - | - In the **Generate Signed Bundle/APK** choose **APK** | + | - In the **Generate Signed Bundle/APK** choose **APK** |
| - The app module should be selected if not choose it or choose a module from the drop down | - The app module should be selected if not choose it or choose a module from the drop down | ||
| - Enter the path to your keystore, the alias for the key and the passwords for keystore and key | - Enter the path to your keystore, the alias for the key and the passwords for keystore and key | ||
| - Enter destination folder for the signed app, enter the release build type, choose the flavor | - Enter destination folder for the signed app, enter the release build type, choose the flavor | ||
| - | - Choose the [[https://source.android.com/security/apksigning#v2|APK Signature version]] your app to support | + | - Choose the [[https://source.android.com/security/apksigning#v2|APK Signature version]] your app to support - v2 for Android 7.0+ |
| - Finish | - Finish | ||
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| In this task will create a signing configuration for different build types. | In this task will create a signing configuration for different build types. | ||
| - Create a release signing configuration with the data from Task 1. [[https://developer.android.com/studio/publish/app-signing#sign-auto|Auto sign]] | - Create a release signing configuration with the data from Task 1. [[https://developer.android.com/studio/publish/app-signing#sign-auto|Auto sign]] | ||
| - | - Build a release version when pressing Run. Check **Build Variants** view from Android Studio. | + | - Build a release version when pressing Run. Check **Build** -> **Select Build Variant** view from Android Studio. |
| - Create a release signing configuration using a new key. | - Create a release signing configuration using a new key. | ||
| - Sign the application wth the new release config and use adb to install the signed apk. You should install the new signed apk on top of the one from item #2. What happens with the application? | - Sign the application wth the new release config and use adb to install the signed apk. You should install the new signed apk on top of the one from item #2. What happens with the application? | ||
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| ==== Task 3 - Generate and Verify HMAC (4p) ==== | ==== Task 3 - Generate and Verify HMAC (4p) ==== | ||
| + | |||
| + | <note tip> | ||
| + | Hash-based message authentication code (HMAC) is a mechanism for verifying the authenticity and integrity of a message. | ||
| + | You can compute it using a hashing crypto algorithm (e.g. SHA-2 family HMAC) and a secret symmetric key. In Android you can use the standard Java API (javax.crypto) for computing it. | ||
| + | </note> | ||
| Add an activity to the project. Include an **EditText** and a **Button** in the first activity. When the user types a text and presses the button, it will send the text to the second activity through an intent (**putExtra**). In the second activity, get the message from the Intent and display it in the **TextView**. | Add an activity to the project. Include an **EditText** and a **Button** in the first activity. When the user types a text and presses the button, it will send the text to the second activity through an intent (**putExtra**). In the second activity, get the message from the Intent and display it in the **TextView**. | ||
| - | In the first activity generate a symmetric key using [[https://developer.android.com/reference/javax/crypto/KeyGenerator|KeyGenerator]] for //HmacSha256// algorithm. Save this key in a Singleton (that can be accessed from both activities). Then generate the HMAC of the text introduced by the user (using **Hmac** with HmacSha256 algorithm) and send the HMAC along with the initial message (through the Intent). In the second activity, obtain the HMAC from the Intent, obtain the Singleton, get the symmetric key and recompute the HMAC. If the HMAC is valid (equal with the recomputed one), Display the message "Data is unmodified". | + | In the first activity generate a symmetric key using [[https://developer.android.com/reference/javax/crypto/KeyGenerator|KeyGenerator]] for //HmacSha256// algorithm. Save this key in a Singleton (that can be accessed from both activities). Then generate the HMAC of the text introduced by the user (using [[https://developer.android.com/reference/javax/crypto/Mac.html|MAC]] with HmacSha256 algorithm) and send the HMAC along with the initial message (through the Intent). In the second activity, obtain the HMAC from the Intent, obtain the Singleton, get the symmetric key and recompute the HMAC. If the HMAC is valid (equal with the recomputed one), Display the message "Data is unmodified". |
| + | |||
| + | Send the data and HMAC as byte arrays in the Intent. Use Arrays.equals() for byte arrays comparison. | ||
| + | |||
| + | <code Java> | ||
| + | String secret = "secret"; | ||
| + | String message = "important message"; | ||
| + | |||
| + | Mac sha256HMAC = Mac.getInstance("HmacSHA256"); | ||
| + | SecretKeySpec secretKey = new SecretKeySpec(secret.getBytes(),"HmacSHA256"); | ||
| + | sha256HMAC.init(secretkey); | ||
| + | byte[] secretMessageBytes = sha256HMAC.doFinal(message.getBytes()) | ||
| + | </code> | ||
| + | |||
| + | |||
| + | |||
| + | |||
| + | ==== Useful Links ==== | ||
| + | * [[smd:laboratoare:07|Lab 7]] | ||
| + | * [[smd:cursuri:06|Lecture 6 - Cryptographic Providers Section]] | ||
| + | * [[https://proandroiddev.com/security-best-practices-symmetric-encryption-with-aes-in-java-7616beaaade9|Security Best Practices: Symmetric Encryption with AES in Java and Android]] | ||
| - | Hint: Send data and HMAC as byte arrays in the Intent.\\ | ||
| - | Hint: Use Arrays.equals() for byte arrays comparison.\\ | ||
| - | Hint: Examples and details about using KeyStore: [[smd:laboratoare:07|Lab 7]] and [[smd:cursuri:06|Lecture 6 - Cryptographic Providers Section]] | ||
