Hello All, There is yet another attack possible against Protected Media Path process beyond the one involving two global XOR keys [1]. The new attack may also result in the extraction of a plaintext content key value. The attack has its origin in a white-box crypto [2] implementation. More specifically, one can devise plaintext content key from white-box crypto data structures of which goal is to make such a reconstruction difficult / not possible. This alone breaks one of the main security objective of white-box cryptography which is to protect the secret key (unbreakability) [3]. Contrary to the initial (XOR key) attack, the white-box crypto attack is not limited to the given narrow time window (white-box data structures need to be present for the time of a movie decryption / playback). Fixing it might require a completely new approach / implementation (current one is obviously flawed). In that context, white-box crypto attack seems to be more severe than the XOR key one. Additionally, a cryptographic check proving that extracted key values correspond to real keys has been conducted for Canal+ Online, Netflix, HBO Max, Amazon Prime Video and Sky Showtime. The check relies on a digital cryptographic signature verification. Such a signature is appended at the end of each license issued by PlayReady license server. The crypto check works as following: - plaintext value of a digital signature key encrypted through ECC is extracted from a Protected Media Path process - the extracted signature key is used to calculate the AES-CMAC value of a binary licence XMR blob - the calculated signature value is checked against the signature appended at the end of the issued license - correct AES-CMAC value implicates correct signature key (and correct content key) The above mechanism is also used by Microsoft to verify the correctness of decrypted content keys received from a license server. It relies on the fact that signature key is part of the same encrypted license blob as content key. Thus, successful extraction of a signature key implicates successful extraction of a content key. In the context of no confirmation / denial [4] from the platforms indicated above as being affected, the crypto check should constitute sufficient proof to support that claim alone. Thank you. Best Regards, Adam Gowdiak ---------------------------------- Security Explorations - AG Security Research Lab https://security-explorations.com ---------------------------------- References: [1] Microsoft Warbird and PMP security research https://security-explorations.com/microsoft-warbird-pmp.html [2] White-box cryptography, Wikipedia https://en.wikipedia.org/wiki/White-box_cryptography [3] White-Box Security Notions for Symmetric Encryption Schemes https://eprint.iacr.org/2013/523.pdf [4] Microsoft DRM Hack Could Allow Movie Downloads From Popular Streaming Services https://www.securityweek.com/microsoft-drm-hacking-could-allow-movie-downloads-from-popular-streaming-services/