Implement MSC3270: Symmetric megolm backup#6984

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BillCarsonFr wants to merge 10 commits intodevelopfrom

feature/fga/msc_3270

Commits on Oct 7, 2022

Symmetric backup : rename megolm algorithm constant and introduce new one

ganfra
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BillCarsonFr
committed
Backup: refactor to extract everything related to specific algorithm

ganfra
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BillCarsonFr
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Backup: introduce Aes256 algorithm

ganfra
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BillCarsonFr
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Extract AesHmacSha2 encrypt/decrypt

ganfra
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BillCarsonFr
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Implement AES backup algorithm (WIP need to check with valere the private key thing)

ganfra
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BillCarsonFr
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Expose setPrivateKey instead of setRecoveryKey as curveKey shouldn't not be used (let valere continue on the privatekey generation)

ganfra
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BillCarsonFr
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added prepare and tests
BillCarsonFr
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Fix bad copy paste breaking 4S restore
BillCarsonFr
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fix copyright
BillCarsonFr
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post rebase fix
BillCarsonFr
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