Change in secure SSL ciphers

We’ve made a technical change to the way our servers handle SSL connections (we’ve disabled 40 bit and 56 encryption ciphers). The change shouldn’t affect anyone, but we’re describing it here just for the record.

When a Web browser makes a secure SSL connection to our servers, it chooses an “encryption cipher” to protect the data. Ciphers have different sizes, such as “40 bit”, “56 bit”, and “128 bit”. Larger ciphers make it much harder for an attacker to “crack” the encryption — for example, it would take 4,722,366,482,869,645,213,696 times as long for an attacker to crack a 128 bit cipher as it would take to crack a 56 bit cipher. So larger ciphers are stronger, which is good.

Unfortunately, when SSL encryption was first invented, the US government had a law that required the use of small, weak ciphers. As a result, many Web browsers supported only 40 bit encryption until 2000, when the law was repealed.

Many people feel that 40 bits, or even 56 bits, isn’t strong enough. A supercomputer can now crack a 56 bit cipher in a matter of hours or days. (It’s unlikely that someone is trying to intercept your SSL connections using a supercomputer, of course, but being paranoid is good security.) So 40 bit and 56 bit ciphers have been considered obsolete for years, and Web browsers since 2000 have included support for 128 bit ciphers.

However, most Web servers, including ours, have continued to accept “obsolete” 40 bit and 56 bit connections from Web browsers for backwards compatibility, using the “if it ain’t broke, don’t fix it” engineering principle.

That was fine until this year, but now credit card companies are adding a new requirement for Web sites that accept credit cards: they no longer permit the use of ciphers smaller than 128 bits. To help our customers comply with that requirement during PCI compliance scans, we have changed our Web server settings to prevent 40 bit and 56 bit connections.

This shouldn’t cause any problems. As far as we know, all Web browser versions issued since 2000 use 128 bit (or higher) connections. Most financial Web sites on the Internet, including banks and paypal.com, have required 128 bit ciphers for some time.

By the way, if you’re wondering whether a 128 bit cipher is going to be obsolete as computers get faster, you probably don’t have to worry. Even if an attacker completely covered the earth one meter deep with the fastest possible supercomputer, it would still take 1,000 years to crack the encryption. We probably won’t need to change things for a while.