Blog Archive for / 2015 / 05 /

Cryptography and Society

Tuesday, 05 May 2015

Politicians in both the UK and USA have been making moves towards banning secure encryption over the last few months. With the UK general election coming on Thursday I wanted to express why I think this is a seriously bad idea.

Context

Back in January there were some terrorist attacks in Paris. These attacks were and are a serious matter, and stopping such attacks in future should be something that governments concern themselves with.

However, one aspect of the response by politicians has been to call for securely encrypted communication outlawed. In particular, the British Prime Minister, David Cameron, asked

"In our country, do we want to allow a means of communication between people which, even in extemis with a signed warrant from the Home Secretary personally, that we cannot read?"

It was clear from the context that he thinks the answer is a resounding "NO", and from the further actions of politicians both here and in the USA it appears that others in government agree with that point of view. They clearly believe that the government should be able to read all communications.

I think in a fair, open, democratic society, the answer must be "YES": private individuals must be able to communicate without risk of eavesdropping by government officials.

Secure Encryption is Not New

Firstly, there have ALWAYS been means of communication between people that the government cannot read. You might be able to intercept a letter, and read the words written on the piece of paper, but if the message is not in the words as they appear, then you cannot read it.

Ciphers which could not be cracked by contemporary eavesdroppers have been used since at least the time of the Roman Empire. New technology merely provides a new set of such ciphers.

For example, the proper use of a one-time pad provides completely secure encryption. This technique has been in use since 1882, if not earlier.

Other technology in widespread use today "merely" makes it exceedingly difficult to break the cipher, requiring hundreds, thousands or even millions of years to crack with a brute-force method. These time periods are enough that these ciphers can be considered uncrackable for all intents and purposes.

Consequently, governments are powerless to actually prevent communication that cannot be read by the security services. All that can be done is to make it hard for the average citizen to use such communication.

Terrorists are Criminals

By their very nature, terrorists are criminals: terrorist acts themselves are illegal, and even the possession of the weapons used for the terrorist acts is often also illegal.

Therefore, terrorists will not be put off from using secure communication just because that too is illegal.

In particular, criminal organisations will not think twice about using whatever means is available to ensure that their communications are private: if something gives them an edge of the police or anyone else who would seek to stop them, they will use it.

Society relies on secure encryption

Secure encrypted communication doesn't just prevent government agencies reading the communications of criminals, it also prevents criminals reading the communications of ordinary citizens.

This website, in common with an increasingly large number of websites, uses HTTPS for all traffic. When properly configured this means that someone intercepting the website traffic cannot identify which pages on the website you visited, or extract any of the data sent by you as a visitor to the website, or by the website back to you.

This is crucial for facilities such as online banking: it prevents computer criminals from obtaining passwords and account data by intercepting the communications between you and your bank. If such communications could not be relied upon to be secure then online banking would not be viable, as the potential for fraud due to stolen passwords would be too great.

Likewise, many businesses use secure Virtual Private Networks (VPNs) which rely on secure encryption to transfer data between computers that are only connected to each other via the internet. This allows them to securely transfer data between sites, or between remote workers, without worrying about the communications being intercepted by criminals. Without secure encryption, many large multi-national businesses would be hugely impacted, as they wouldn't be able to rely on transferring data across the internet safely, and would instead have to rely on physical transfer via courier.

A "back door" or "government secret key" destroys the security of encryption

Some of the proposals from politicians have been to require that companies that provide encryption services must also provide a means whereby government security services can also decrypt the communications if required.

This requires that either (a) the company in question keeps a database of all the encryption/decryption keys used for all communications, or (b) the encryption algorithm used allows for decryption via a "back door" or "secret key" in addition to the standard decryption key, so that the government security services can gain access if required, without needing to know the customer's decryption key.

Keeping a database of the decryption keys just provides a direct target for attack by computer criminals. Once such a database is breached, none of the communications provided by that company can be considered secure. This is clearly not a good state of affairs, given the number of times that password databases get compromised.

That leaves option (b): providing a "back door" or "secret key", or other means whereby an otherwise-encrypted communication can be read by the security services. However, this fundamentally compromises that encryption.

Knowing that the back door exists, criminal computer crackers will work to ensure that they too can gain access to the communication, and they won't wait for a warrant from the Home Secretary or whatever government department is responsible for issuing such warrants! Any such group that does manage to obtain access would probably not make it public knowledge, they would merely use it to ensure that they could access communications that were relevant to them, whether that was because they had a direct use for the information, or because it could be sold to other criminal organisations.

If there is a single key that can decrypt all communication using a given system then that dramatically reduces the computation effort required to break the key: the larger the number of messages that are transmitted with a given key, the easier it is to identify the key, especially if you have access to the raw unencrypted message. The huge volume of electronic communications in use today would mean that the secret back door key would be much more readily compromised than any individual encryption key.

Privacy is a human right

The Universal Declaration of Human Rights was adopted by the UN in 1948. Article 12 states:

No one shall be subjected to arbitrary interference with his privacy, family, home or correspondence, nor to attacks upon his honour and reputation. Everyone has the right to the protection of the law against such interference or attacks.

Secure encrypted communication protects our correspondence from interference, including interference by the government.

Restricting the use of encryption is also a violation of the right to freedom of expression, guaranteed to us by article 19 of the Universal Declaration of Human Rights:

Everyone has the right to freedom of opinion and expression; this right includes freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers.

The restriction on our freedom of expression is easy to see: if I have true freedom of expression then I can impart any series of letters or numbers to anyone without interference. If that series of letters or numbers happens to be an encrypted message then that is of no consequence. Any attempt to limit the use of particular encryption algorithms therefore limits my ability to send whatever message I like, since particular sequences of letters and numbers are outlawed purely because of their meaning.

Human rights organisations such as Amnesty International use secure encrypted communications to communicate with their workers. If those communications could not be secured against interference then this would have a detrimental impact on their ability to do their humanitarian work, and could endanger their workers.

Encryption is mathematics

Computer encryption is just a mathematical algorithm applied to a series of numbers. It is ridiculous to consider that performing mathematical operations on a sequence of numbers could be outlawed merely because that sequence of numbers has meaning to someone.

End note

I strongly object to any move to restrict the use of encryption technology. It is technologically and morally unsound, with little or no upside and considerable downsides.

I urge politicians to likewise oppose any moves to restrict the use of encryption technology, and I urge those standing in the elections in the UK this week to make it known to their potential constituents that they will oppose such measures.

Finally, I think we should be encouraging the use of strong encryption rather than discouraging it, to protect us from those who would intercept our digital communication and use that for their gain and our detriment.

Posted by Anthony Williams
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Tags: cryptography, encryption, politics
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