Client-browser readme is missing fallback strategies and alternatives

[juneb]

The fallback section of the readme for the client-browser module lists the features of the SDK that are not supported by certain browsers. However, while it mentions msrcrypto as an example of a fallback library, it doesn't recommend any fallback strategies or alternatives.

Also, the fallback section points to @aws-crypto/web-crypto-backend, but that file has very little information, and just sends readers back to the readme. Loops like this are very frustrating to users.

[khadir-syed]

Hi,

Any further information on this is really helpful, we currently have requirement where we are using AWS encryption SDK for browser using javascript and we are facing compatibility issues with safari browser on MAC and iOS devices. If any information on this will be helpful, till readme documentation is updated.

[seebees]

@khadir-syed Safari does not support Zero-Byte AES-GCM operations. So a fallback (such as msrcrypto) is needed. Even though WebCrypto is supported.

[khadir-syed]

@seebees - Thanks for your reply. As per below documentation client-browser module, I configured fallback and still seeing issue.

============================

WebCrypto availability
The WebCrypto API is not available on all browsers. A fallback can be configured. An example of a fallback library is: MSR Crypto

import { configureFallback } from '@aws-crypto/client-browser'
configureFallback(msrCrypto)

For details on configureFallback see: @aws-crypto/web-crypto-backend

============================

Mainly error is coming in configureFallback function. This is the error.

Unhandled Promise Rejection: Error: A Fallback is required for zero byte AES-GCM operations.

Do I need to do any spec \ additional changes in web-crypto-backend module? Thanks in advance.

[seebees]

If you have a public repo I could take a look.
The error you are referencing should be throw here: https://github.com/aws/aws-encryption-sdk-javascript//blob/master/modules/web-crypto-backend/src/backend-factory.ts#L55
That error suggests that the code is running on safari and that a fallback has not been configured.

Are you sure that you are not getting an error on configureFallback(msrCrypto)?

[khadir-syed]

@seebees - you can check this public code repo - https://github.com/khadir-syed/aws_sdk_encryption_js_poc

I have done changes in these files - https://github.com/khadir-syed/aws_sdk_encryption_js_poc/blob/master/node_modules/%40aws-crypto/example-browser/src/aes_simple.ts

where I added below code

import { configureFallback } from '@aws-crypto/client-browser'
configureFallback(msrCrypto)

msrCrypto is present in node_modules here - https://github.com/khadir-syed/aws_sdk_encryption_js_poc/tree/master/node_modules/%40aws-crypto/example-browser/node_modules

aes_simple_bundle.js - is created using npm run example-aes, present in https://github.com/khadir-syed/aws_sdk_encryption_js_poc/tree/master/node_modules/%40aws-crypto/example-browser/build and it is referened in aes_simple.html file which is present in this locaiton https://github.com/khadir-syed/aws_sdk_encryption_js_poc/tree/master/node_modules/%40aws-crypto/example-browser/html

msrcrypto.js - This I referenced in above html file, below is for your reference.

<script src="../node_modules/msrcrypto/msrcrypto.js"></script>
<script src="../build/aes_simple_bundle.js"></script>

Also, I am attaching screen shots from chrome and safari browers on MAC machine I am testing...

Any help here is much appreciated, as I am struck on this from sometime.

[seebees]

The fallback conversation was resolved by #239,
There is now a example illustrating this.