Added MasterkeyHubAccess

[overheadhunter]

Added MasterkeyHubAccess, which allows decryption of device-specific masterkeys used in Cryptomator Hub.

This facilitates ECIES with:

• P-384 curves
• ANSI X9.63 KDF with SHA-256 deriving a 256 + 96 bit secret
• AES-GCM with a 256 bit KEK and 96 bit nonce* (derived by KDF)
• No separate MAC required, as a tag is included in GCM ciphertexts

* The nonce is unique due to the nature of ECIES which facilitates ephemeral key pairs: The private key is immediately discarded during encryption, reuse is impossible when correctly implemented.

[overheadhunter]

@SailReal Once again, can you please test this on Android 7.x? Basically copy this test over to your Android code base and see if it works. Thanks! 🙂

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

81.5% Coverage
0.0% Duplication

[SailReal]

LGTM, tested it using MasterkeyHubAccessTest as well as with GcmWithSecretNonceTest on Android 8.0 and Android 11

[infeo]

For Documentation: This feature was removed again in 47a6c2c