Add KeyStoreBackedSecretKeyProvider, Fixes AB#3274176

[p3dr0rv]

Summary

This PR has two main goals: to seamlessly update the encryption padding used in the Android KeyStore, and to lay the groundwork for integrating future cryptographic requirements with minimal changes.

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Phase 1: Replace AndroidWrappedKeyProvider with KeyStoreBackedSecretKeyProvider

• Controller Flag: ENABLE_KEYSTORE_BACKED_SECRET_KEY_PROVIDER

• Behavior When Enabled:

  • The factory will return KeyStoreBackedSecretKeyProvider instead of AndroidWrappedKeyProvider.
  • The new class behaves similarly to the previous one but introduces the ability to:
    • Retrieve the paddings supported by the KeyStore KeyPair
  • Maintain a list of available ciphers (oaepCipherSpec and pkcs1CipherSpec)
  • Select a compatible cipher for encryption/decryption based on what the KeyPair supports.
    • In this case, if the KeyPair only supports PKCS1, then all keys will be encrypted and decrypted using PKCS1.

• Goal:

  • Validate that the new provider functions equivalently to the existing one.

  Note: No encryption changes are introduced in this phase.

Tests

• AndroidWrappedKeyProviderTest has been parameterized to confirm both providers behave identically.
• KeyStoreBackedSecretKeyProviderRolloutTest.java includes test to validate migration and rollback

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Phase 2: Enable New Wrapped Secret Key Format with Metadata Support

Before introducing new key types, we need to ensure that all new keys include additional metadata that specifies how they were encrypted.

• Controller Flag: ENABLE_NEW_WRAPPED_SECRET_KEY_FORMAT

• Behavior When Enabled:

  • WrappedSecretKey will use an enhanced binary format with the following structure:
    • MAGIC BYTES (4 bytes)
    • SERIALIZER ID (4bytes)
    • Metadata length (4 bytes)
    • Metadata (format is decided by the serializer)
    • Raw encrypted key bytes

• Goal:

  • Future-proof the wrapped key by including metadata that specifies:
    • Key size
    • Algorithm
    • Transformation used for encryption
    • Key version
  • This allows the system to handle multiple key types if formats change in the future.
  • Validate WrappedSecretKey can read both new and old keys.

Tests

• WrappedSecretKeyTest

---

Phase 3: Add OAEP encryption padding.

• Controller Flag: ENABLE_OAEP_WITH_SHA_AND_MGF1_PADDING

• Behavior When Enabled:

  • CryptoParameterSpecFactory will now return two paddings: ENCRYPTION_PADDING_RSA_PKCS1 and ENCRYPTION_PADDING_RSA_OAEP for the KeyGen specifications.
  • KeyStoreBackedSecretKeyProvider will generate a KeyPair that supports ENCRYPTION_PADDING_RSA_OAEP.
  • As a result, when a SecretKey needs to be wrapped, the provider will select OAEP, since the KeyPair now supports this padding and OAEP cipher support was already introduced in Phase 1.

• Goal:

  • All new keys will be encrypted /decrypted with OAEP
  • Existing keys will still be encrypted /decrypted with PKCS1

Tests

• KeyStoreBackedSecretKeyProviderRolloutTest.java includes test to validate migration and rollback

---

Telemetry

span_name	key_pair_gen_successful_method	elapsed_time_keypair_generation	secret_key_wrapping_cipher	secret_key_wrapping_operation
SecretKeyWrapping	null		CipherSpec(transformation='RSA/ECB/PKCS1Padding')	KeyStoreBackedSecretKeyProvider:unwrapSecretKey
KeyPairGeneration	KeyGenSpec(description='modern_spec_with_wrap_key', algorithm='RSA', encryptionPaddings='[PKCS1Padding]')	581
KeyPairGeneration	KeyGenSpec(description='modern_spec_with_wrap_key', algorithm='RSA', encryptionPaddings='[PKCS1Padding]')	294

AB#3274176
https://github.com/AzureAD/ad-accounts-for-android/pull/3166

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[p3dr0rv]

Is there any reason why Phase 2 and phase 3 should not be done together?

There’s no limitation in the code; I chose this approach so that in case of a rollback, it’s easier to move from one state to another. It also provides more granularity in the release, allowing us to ensure that each step of the new changes works as expected.

[mohitc1]