Support encryption key in configuration

[desistefanova]

Support encryption key used to encrypt the entire [Realm].
Its length is forced to be 64bytes.
If null encryption is not enabled.
Fixes #88

[nirinchev]

Looks great, just a few suggestions and would like to see more tests.

[coveralls]

Pull Request Test Coverage Report for Build 3111528733

• 0 of 4 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+5.5%) to 93.128%

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Totals
Change from base Build 3097932778:	5.5%
Covered Lines:	393
Relevant Lines:	422

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 3218450209

• 11 of 11 (100.0%) changed or added relevant lines in 2 files are covered.
• 150 unchanged lines in 8 files lost coverage.
• Overall coverage increased (+4.5%) to 92.558%

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Files with Coverage Reduction	New Missed Lines	%
lib/src/list.dart	2	88.68%
lib/src/session.dart	2	89.66%
lib/src/subscription.dart	2	91.03%
lib/src/results.dart	3	91.53%
lib/src/scheduler.dart	3	61.54%
lib/src/realm_object.dart	5	85.85%
lib/src/realm_class.dart	13	91.71%
lib/src/native/realm_core.dart	120	88.45%

Totals
Change from base Build 3181931773:	4.5%
Covered Lines:	398
Relevant Lines:	430

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💛 - Coveralls

[nirinchev]

One final question from me, otherwise it looks good.

[richard457]

I am writing to request clarification on the encryption key when passed, when added to realm later will it encrypt the existing realm?

[richard457]

also the example from docs shows encrypting local realm

// Generate encryption key
--
final key = List<int>.generate(64, (i) => Random().nextInt(256));
 
final encryptedConfig = Configuration.local([Car.schema],
// Include the encryption key in the configuration
encryptionKey: key);
final encryptedRealm = Realm(encryptedConfig);

does it work on flexible sync as well @desistefanova

[nirinchev]

Yes, it works with flexible sync and no - you cannot change the encryption of a file after it was created. You can use Realm.writeCopy to create an encrypted copy of the file, but that only works for local files. For synchronized realms, you can just recreate the file and re-fetch the data.