AS3 - Base64Encoder?

I’m using the Flash 9 preview, and having some problems with the SHA1 class included in the corelib found on Adobe Labs’ site. This SHA1 class tries to make use of mx.utils.Base64Encoder, which doesn’t seem to exist anymore. I can’t find it in the AS3 reference.

What happened to it? What should I do to make Base 64 encoding work?