(#) Weak RNG !!! WARNING: Weak RNG This is a warning. Id : `TrulyRandom` Summary : Weak RNG Severity : Warning Category : Security Platform : Any Vendor : Android Open Source Project Feedback : https://issuetracker.google.com/issues/new?component=192708 Since : Initial Affects : Class files Editing : This check runs on the fly in the IDE editor See : https://goo.gle/TrulyRandom See : https://android-developers.blogspot.com/2013/08/some-securerandom-thoughts.html Implementation : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/SecureRandomGeneratorDetector.java) Tests : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/SecureRandomGeneratorDetectorTest.java) Copyright Year : 2013 Key generation, signing, encryption, and random number generation may not receive cryptographically strong values due to improper initialization of the underlying PRNG on Android 4.3 and below. If your application relies on cryptographically secure random number generation you should apply the workaround described in https://android-developers.blogspot.com/2013/08/some-securerandom-thoughts.html . This lint rule is mostly informational; it does not accurately detect whether cryptographically secure RNG is required, or whether the workaround has already been applied. After reading the blog entry and updating your code if necessary, you can disable this lint issue. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/test/pkg/PrngCalls.java:13:Warning: Potentially insecure random numbers on Android 4.3 and older. Read https://android-developers.blogspot.com/2013/08/some-securerandom-thoughts.html for more info. [TrulyRandom] KeyGenerator generator = KeyGenerator.getInstance("AES", "BC"); ----------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/test/pkg/PrngCalls.java`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers package test.pkg; import java.security.KeyPairGenerator; import java.security.NoSuchAlgorithmException; import java.security.NoSuchProviderException; import java.security.SecureRandom; import javax.crypto.KeyAgreement; import javax.crypto.KeyGenerator; public class PrngCalls { public void testKeyGenerator() throws NoSuchAlgorithmException, NoSuchProviderException { KeyGenerator generator = KeyGenerator.getInstance("AES", "BC"); generator.init(128); KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA"); keyGen.initialize(512); KeyAgreement agreement = KeyAgreement.getInstance("DH", "BC"); agreement.generateSecret(); SecureRandom random = new SecureRandom(); byte bytes[] = new byte[20]; random.nextBytes(bytes); } } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/SecureRandomGeneratorDetectorTest.java) for the unit tests for this check to see additional scenarios. The above example was automatically extracted from the first unit test found for this lint check, `SecureRandomGeneratorDetector.testWithoutWorkaround`. To report a problem with this extracted sample, visit https://issuetracker.google.com/issues/new?component=192708. (##) Suppressing You can suppress false positives using one of the following mechanisms: * Using a special `lint.xml` file in the source tree which turns off the check in that folder and any sub folder. A simple file might look like this: ```xml <?xml version="1.0" encoding="UTF-8"?> <lint> <issue id="TrulyRandom" severity="ignore" /> </lint> ``` Instead of `ignore` you can also change the severity here, for example from `error` to `warning`. You can find additional documentation on how to filter issues by path, regular expression and so on [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html). * In Gradle projects, using the DSL syntax to configure lint. For example, you can use something like ```gradle lintOptions { disable 'TrulyRandom' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore TrulyRandom ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).