[Second post in a series on why encryption is not the silver bullet for the case of General Petraeus and Paula Broadwell]
2. Encryption does not hide traffic patterns
The first half of this discussion centered on usability challenges of encrypting email with common cloud-based email providers, and how their web interfaces did not exactly help in this endeavor. It turns out that even for the very patient users willing to invest the extra effort and incur the overhead of setting up encryption, it would have made no difference against the type of surveillance FBI is believed to have conducted in this case.
First the threats sent by Ms. Broadwell to Ms. Kelley had to be readable by the recipient. Even if they were encrypted, Ms. Kelley would have voluntarily revealed their contents to law enforcement since it was at her urging that the FBI began investigating the source of these communications. NBC coverage suggests that FBI only relied on location history for that account (IP addresses and timestamps) to determine the owner. In fact since it is described as an “anonymous” account, it is possible that Ms. Broadwell limited its use to sending those warning shots, never corresponding with other persons that could link the account to her true identity. In other words, the investigators had to rely on metadata for unmasking the sender.
Once Ms. Broadwell’s identity was established– presumably by obtaining access to other accounts accessed from the same IP addresses– law enforcement had access to correspondence sent from these additional accounts. Let’s suspend disbelief and assume that 100% of communications to/from that account were encrypted. This would not have prevented obtaining metadata about other email addresses observed to be frequently communicating with Ms. Broadwell and performing similar analysis to establish the link to General Petraeus.
As several commentators pointed out, using an anonymizing proxy such as Tor— even when limited to the one-off email account– could have helped with obscuring IP addresses.
3. Encryption would have drawn more attention to the sender
In reality of course not all of the correspondence discovered in Ms. Broadwell’s account would be encrypted. Most of it is routine chatter with friends and associates that does not warrant the extra hassle of using cryptography. When only a few senders in the address book are using encryption, these contacts immediately stand out. Given Ms. Broadwell’s level of security clearance and access to the inner circle of national security leadership, it would have been an alarming discovery that she is corresponding with unknown individuals from a personal email account using strong cryptography.
It’s a murky picture around the question of whether individuals can be legally compelled to decrypt their own communications to aid an investigation. But once investigators had uncovered a frequent pattern of encrypted traffic between General Petraeus and a suspect in an investigation under suspicion of mishandling classified information, either or both sides of that exchange would come under enormorous pressure to come clean by revealing cleartext version of their correspondence– irrespective of whether they can be forced to, as matter of due process.