I'm betting Jeph never explains the exact mechanics of whatever this encrypted memory business is; he may just leave it at saying that CW has some sort of hold over Bubbles based on some sort of secret data.
I sort of hope this is true, because all the confident theories I'm reading are not 100% convincing to me.
The popular theory seems to be that CW has encrypted some memories of Bubbles that are too traumatic to be endured, and that CW is threatening to unencrypt them. But I have questions. How does that mesh with "defaulting on memories?" How can CW unencrypt Bubbles' memories against her will? How does CW unencrypting those memories force them onto Bubbles? Why can't, or couldn't, Bubbles encrypt them herself?
Another theory is that Bubbles
wants the key that CW is holding so that she can access memories that she previously locked away. That meshes a bit better with what CW said, but I'm not seeing that Bubbles currently wants those memories back. Also, if this is the correct scenario, CW already has the key, so what is she threatening in that case? She can't take away something she already has. Or did she promise to give Bubbles the key at a future time or event, which she is now hinting she will not do, or be able to do if she is killed? How can Bubbles trust that she would hold to that, in that case?
Yet another theory, and one that I don't think I've yet seen, is that a
third party has access to the memories, but cannot decrypt them because CW has the key. In this scenario, CW is threatening to hand the key to the third party, which would lead to them discovering what the memories contain, causing repercussions for Bubbles. This meshes well with the threat of "defaulting on memories," and also with May's speculation that Bubbles is not innocent. But how did this third party get access to these encrypted memories, anyway?
It's all a bit vague and confusing, and I suspect that this is deliberate. We may well find out more in the future, or the hold CW has over Bubbles may be broken without us learning the details.
My feeling is that the solution will not be technological, regardless of the mechanism of this threat. The challenge for Bubbles will be for her to properly confront the demons of her past and, in so doing, release the hold that CW has over her. That would seem to fit the general theme of Bubbles' overall story arc.
/braindump