CipherSharedPrefs

Additional

Language
Kotlin
Version
1.0.2 (Jun 20, 2018)
Created
Mar 24, 2017
Updated
Jun 20, 2018
Owner
Mykyta Sizyntsev (Ufkoku)
Contributor
Mykyta Sizyntsev (Ufkoku)
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CipherSharedPrefs

CipherSharedPrefs implements SharedPreferences with encryption layer and some new features.

repositories {
    maven { url 'https://dl.bintray.com/ufkoku/maven/' }
}

dependencies {
    compile 'com.ufkoku.cipher_sharedprefs:sharedprefs:version'
    //or
    compile 'com.ufkoku.cipher_sharedprefs:sharedprefs:version@aar'{
        transitive = true
    }
}

How it works

When you put value to CipherSharedPreferences it is transformed to String and encrypted by provided ICipherHolder object, encryped string is saved to SharedPreferences delegate.

new CipherSharedPreferences(
                context.getSharedPreferences(SHARED_PREFS, Context.MODE_PRIVATE),
                iCipherHolder,
                iCacheHolder, //optional
                iTransformer //optional
        )

Cipher

You must provide implementation of ICipherHolder to CipherSharedPreferences constructor. It is used for data encryption and decryption.

Library contains AES implementation AesCipher.

  • Default mode: ECB;
  • Supported modes: CBC, CFB, CTR, ECB, OFB;
  • IV requires modes: CBC, CFB, OFB, CTR;
  • Supported keys: Supported size 128/192/256 bits -> 16/24/32 bytes;
  • IV lenght: equals to key lenght;

IV - initialization vector

dependencies {
    compile 'com.ufkoku.cipher_sharedprefs:ciphers:version'
    //or
    compile 'com.ufkoku.cipher_sharedprefs:ciphers:version@aar'{
        transitive = true
    }
}

Cache (Optional)

You can provide ICacheHolder to CipherSharedPreferences.

If ICacheHolder exists, values WITHOUT encryption will be saved there, after get/put methods for key.
When you call get methods, CipherSharedPreferences checks cache, and if value exists - it will be returned, otherwise it will be decrypted from delegate, and saved to cache.
When you call put methods, CipherSharedPreferences saves value to cache WITHOUT encryption, and encrypted string to delegate.

PROS

  • When you getting value, that contains in cache, you are not spending time on decryption.

LIMITATIONS

  • If you use cache, you should use CipherSharedPreferences or ICacheHolder as singleton, cache won't be refreshed if you modify prefs from another instance.

There are already implemented cache holders, that you can use in module caches

dependencies {
    compile 'com.ufkoku.cipher_sharedprefs:caches:version'
    //or
    compile 'com.ufkoku.cipher_sharedprefs:caches:version@aar'{
        transitive = true
    }
}

Implementations:

  • SharedPrefsLruCache wrap over SizeBasedEnhancedLruCache, it limits cache by size in bytes.
  • SharedPrefsMapCache wrap over HashMap

Object saving (Optional)

CipherSharedPreferences can save objects and retrieve them back via methods

CipherSharedPreferences {
    
    //get object
    <T> getObject(key: String, defValue: T?, clazz: Class<T>): T?

    CipherEditor{
        //save object
        putObject(key: String, value: Any?): SharedPreferences.Editor
    }

}

To use this feature you need to provide ITransformer implementation to CipherSharedPreferences constructor.

//Example of ITransformer
//This transformer uses GSON to transform input objects to string and back.
transformer = new ITransformer() {
            private Gson gson = new Gson();

            @NotNull
            @Override
            public String toString(@NotNull Object o) {
                return gson.toJson(o);
            }

            @Override
            public <T> T fromString(@NotNull String string, @NonNull Class<T> clazz) {
                return gson.fromJson(string, clazz);
            }
            
        };

Example of usage

        Set<String> value = new HashSet<>();
        value.add("str1");
        value.add("str2");
        value.add("str3");
        
        preferences.edit().putObject(KEY_1, value).commit();
        preferences.getObject(KEY_1, null, value.getClass())