TypeError: Attempted to assign to readonly property.

[miguelmota]

Safari error

[StefanStadler]

I encountered the same issue with Safari 11 release
in Safari 10 it works as expected

probably related to:
The Crypto.subtle read-only property returns a SubtleCrypto object allowing to perform cryptographical operations.
https://developer.mozilla.org/en-US/docs/Web/API/Crypto/subtle

[akselnordal]

Safari 11 should be standards compliant regarding the WebCrypto interfaces and not in need of webcrypto-shim. The feature tests should be updated to not eval the shim code for Safari 11

More info:
https://webkit.org/blog/7790/update-on-web-cryptography/

[vibornoff]

@miguelmota , make sure you're using the latest version.