Parent pretty much sums it up. As it stands now you have to buy a license to decrypt HDCP, and you get a key to do so. If you do not abide by the terms of the license, your key can get revoked and these revoked keys can be embedded in a content stream to block usage by the offending hardware. Though I am unaware of any that have been at this time.
I have in front of me a piece of hardware (that I have been developing on), that actually has a HDMI input and "may" be capable of decrypting that stream. I could then convert that stream into an IP stream, QAM, or even record to disk. However, the HDCP license forbids re-transmitting that stream over long distances in the clear or storing as such. So now this box is legally only capable of handling un-encrypted HDMI signals. I'm wondering if this information may allow devices to masquerade as a device from another manufacturer. Not that I would do that myself, but it seems that it could make "software" HDCP decryption systems more common. The software description is used loosely since much of this is currently handled in hardware or FPGA sub-systems.