According to technical reports by the Royal Canadian Mounted Police that were filed in court, law enforcement intercepted and decrypted roughly one million PIN-to-PIN BlackBerry messages in connection with the probe. The report doesn't disclose exactly where the key — effectively a piece of code that could break the encryption on virtually any BlackBerry message sent from one device to another — came from.
The actual, honest-to-God global master BlackBerry encryption key.
See also Motherboard's reporting on this issue and the revelation that PGP-protected BlackBerrys are also hackable.