Use WebCrypto APIs for AES & SHA operations

[zone117x]

Related issues:

• Ensure that ID creation screen is fast across devices stacks-archive/blockstack-browser#1900
• Use of deprecated crypto functionality in newer versions of Node #681
• putFile crashes Safari on iOS when uploading many encrypted files. #564

Current associated PR: #737
Initial experimental PoC PR: #659

Solve some of the CPU & memory issues with our crypto operations, especially as it relates to:

• User account registration and restoration.
• File encryption and decryption in the storage APIs.

Tasks:

• Replace usage of Node.js crypto lib in the auth and storage modules with modern WebCrypto APIs.

  • Currently, when packaged for the web, Node.js crypto gets polyfilled with IE-era JS implementations. These are both large in file size, and CPU & memory inefficient. One symptom is significant lag during the related authenticator pages, especially on low-powered mobile devices.

• Strategy for handling breaking changes for some public blockstack.js functions that must be converted from sync to async.

  • This PR is currently dealing with how to handle breaking changes on most of these same functions: Make the SessionStore asynchronous #679

• (Optional / not sure) Strategy for making downstream dependencies -- mostly bitcoinjs-lib & family packages -- to use W3C crypto APIs rather than the Node.js crypto polyfills or other redundant libs.

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Projects that need updated -- higher priority:

• blockstack-keychain (draft PR opened w3c crypto stacks-archive/keychain#10)
• blockstack-browser (draft PR opened Use blockstack.js W3C crypto stacks-archive/blockstack-browser#1966)
• gaia (draft PR opened [Do not merge] Blockstack.js async crypto stacks-archive/gaia#272)
• blockstack-cli (draft PR opened [Do not merge] Blockstack.js async crypto stacks-archive/cli-blockstack#27)

Lower priority:

• iOS SDK
• Android SDK (uses its own native crypto functions?)
• react native SDK (?)
• Wallet app