SAN FRANCISCO—While Apple faces down the FBI in court and law enforcement calls for backdoors to encryption services, a researcher at the RSA Conference here asked an important question: Would backdoors actually help?
Crypto expert Klaus Schmeh, currently a consultant at Cryptovision used his knowledge of cryptography and some lengthy Googling to see if backdoors could have made a difference in criminals cases. His answer: probably not.
The CasesAfter 20 days of combing through news websites, Schmeh found a corpus of 50 criminal cases that involved encryption in some way. Of these, the majority (16 cases) were about child pornography.
Another seven cases were murders, six were terrorism-related, and five involved espionage.
The other 16 cases fell into various other categories.
In 33 of the 50 cases, the police were not able to break or bypass the encryption.
In fact, they were only successful in 11 cases, with several unaccounted.
In all the cases, the encrypted files were obtained by confiscating a device of some kind.
This surprised Schmeh, who expected to find at least a few cases of wiretapping or data interception. However, it might simply be that in those cases, law enforcement did not wish to discuss the use of such controversial tactics. “In most cases the police lost, and this is certainly one of the reasons why [FBI Director] Comey wants to have backdoors in encryption products,” said Schmeh.
An interesting point is that in two of the 50 cases Schmeh profiled, it was the victim of the crime and not the suspect or perpetrator who held encrypted information.
Do Backdoors Work?In all the cases Schmeh looked at, 25 were solved without the police breaking the encryption.
In only three out of the 50 cases did police neither solve the crime nor crack the encrypted files.
This, said Schmeh, revealed that backdoors are not a “magic bullet” for investigations.
“It would have been crucial, but would not have been a guarantee,” said Schmeh.
In the cases where law enforcement was able to decrypt the files, it was primarily by circumventing the encryption.
In the case of Anna Chapman, the Russian spy captured in the U.S., investigators found a piece of paper where Chapman had written her passwords.
In another case, an FBI agent downloaded the contents of an encrypted Personal Digital Assistant that the suspect had left unlocked.
Schmeh also mentioned one case, where it seemed like Canadian law enforcement successfully brute-forced a password with random guesses, but it took 2.5 years to complete.
Call for HelpSchmeh proposed one alternative to adding a backdoor to encryption system, or forcing companies to create specialized tools to break open secured devices. He suggested the police could publish the ciphertext—that is, the encrypted text—and ask the public for assistance in breaking it.
Encryption systems that use a password-derived key (and not a public key), Schmeh explained, frequently have an encrypted keycheck string before the ciphertext.
That keycheck string can be separated from the ciphertext and subjected to a brute-force attack that will eventually yield the correct key and, in turn, the password to decrypt the rest of the ciphertext.
This approach, said Schmeh, would allow law enforcement to crowdsource a solution while still keeping the ciphertext secret.
Interestingly, Schmeh had several historical examples of law enforcement having published ciphertext in an effort to help an investigation. While many of these were fascinating (and mysterious!) they were all examples of classical or manual encryption.
Basically codes written out by hand, and not the complex algorithm-driven encryption used in digital devices today.
Don’t Open the DoorIt’s important to note the distinction between backdoors in encryption and what Apple is currently fighting in the courts.
Apple’s complaint hinges on being asked to create a special version of iOS that would allow the FBI to unlock the phone themselves.
A backdooor for encryption, on the other hand, would create some kind of mechanism for law enforcement to decrypt files without the key.
The research Schmeh presented focused on encrypted drives and files, and scenarios where police would want backdoors, not the kind of tool the FBI wants from Apple.
That’s not to say that there aren’t those in Washington calling for the creation of backdoors.
Attorney General Loretta Lynch said during her speech at RSA that encryption could thwart law enforcement. Using the phrase often used when attacking encryption, she said that “going dark is a very real issue.” On the opposite side, Secretary of Defense Ashton Carter said at RSA that he did not support backdoors and that he support strong encryption.
Schmeh was humble in his presentation, taking pains to point out the limitations of his research. He was, for example, limited to reports in the public press and in languages he could read.
There were also several cases where the press had insufficient details.
But still, he concluded that backdoors were too much of a risk to employ.
“There will be some cases where police might profit from backdoors, but there aren’t too many of them in my collection.
They might be helpful in some cases, but the price we pay for them is too high,” concluded Schmeh.