Step 1: Find Your Key Number. It is only possible to obtain a replacement key from Master Lock® if you have the key number. Your key number can be found on the back of your key or on the original packaging. For example, this key number is 3900. The Master Lock No. 6KA Laminated Brass Padlock, Keyed Alike – multiple locks open with the same key - features a 2in (51mm) wide laminated brass. View full details Master Lock 1525 General Security Combination Padlock with Key Control Feature 1-7/8in (48mm) Wide.

• Master Lock Serial Number List For Singer Sewing Machines
• Master Lock Serial Number List By Lars Kirmser

There's a vulnerability in Master Lock branded padlocks that allows anyone to learn the combination in eight or fewer tries, a process that requires less than two minutes and a minimal amount of skill to carry out.

The exploit involves lifting up a locked shackle with one hand while turning the combination dial counterclockwise starting at the number 0 with the other. Before the dial reaches 11, there will be three points where the dial will resist being turned anymore. One of them will be ignored as it is exactly between two whole numbers on the dial. The remaining two locations represent locked positions. Next, an attacker again lifts the locked shackle, this time with less force, while turning the dial clockwise. At some point before a full revolution is completed, the dial will resist being turned. (An attacker can still turn through it but will physically feel the resistance.) This location represents the resistance location. The two locked positions and the one resistance position are then recorded on a Web page that streamlines the exploit.

The page responds with the first digit of the combination and two possible digits for the last digit. By testing which of the possible last digits has more 'give,' an attacker can quickly figure out which one is correct. By eliminating the false digit from the Web form, the page will automatically populate the eight possible numbers for the second digit of the combination.

Now that the attacker knows the first and last digits and knows the second digit is one of eight possible numbers, the hack is a simple matter of trying each possible combination until the correct one opens the lock. The following video provides a simple tutorial.

The technique was devised by Samy Kamkar, a serial hacker who has created everything from stealthy keystroke-pilfering USB chargers to DIY stalker apps that mined Google Streetview. In 2005, he unleashed the Samy worm, a cross-site scripting exploit that knocked MySpace out of commission when it added more than one million MySpace friends to Kamkar's account.

Kamkar told Ars his Master Lock exploit started with a well-known vulnerability that allows Master Lock combinations to be cracked in 100 or fewer tries. He then physically broke open a combination lock and noticed the resistance he observed was caused by two lock parts that touched in a way that revealed important clues about the combination. (He likened the Master Lock design to a side channel in cryptographic devices that can be exploited to obtain the secret key.) Kamkar then made a third observation that was instrumental to his Master Lock exploit: the first and third digit of the combination, when divided by four, always return the same remainder. By combining the insights from all three weaknesses he devised the attack laid out in the video.

It's by no means the only way to break the security of a popular padlock. It comes a few years after Master Lock engineers developed new padlocks that resisted a popular form of attacks using shims made from soft drink cans. Kamkar said he has tried his exploit on more than a dozen Master Lock combination locks, and so far it has worked on all of them. In the coming weeks, he plans to unveil more details, including an Arduino-based robot that streamlines the exploit.

Post updated to change 'any' in the headline to 'many.'

Watch Ars staffers put the hack to the test.

Master Lock Serial Number List For Singer Sewing Machines

Combination locks are great for school, gym, and any other personal use lockers! However, losing your combination can be frustrating. Below we’ll cover ways to help you recover any lost combinations*, and our tips on preventing being locked out of your combination lock again!

*Please note that it is only possible to retrieve missing combinations if your combination lock has a serial number written on the back, and is not attached or locking anything. See the image below to ensure that your lock has a serial number.

If your combination lock does not provide a serial number, there is no documentation on which combination your lock may have. Unfortunately, this means that looking for documentation or old packaging may be the only way to recover your combination. If you are need of a new combination lock, visit us at Masterlocks.com to purchase one at a great price.

If your lock does provide a serial number, the easiest way to retrieve your combination is to take your lock to any local Master Lock Distributor in your area; think of Wal-Mart, Home Depot, Lowes, etc. A store associate at the customer service desk will be able to call the Master Lock Customer Service line at 1(800)308-9244 to retrieve your combination for you. It’s important to note that Master Lock will not release combinations to anybody other than authorized employees who can vouch that your lock is in hand, present, and free standing.

Now that you have access to your combination, we recommend you store it in a safe place. The best place for storing your combination is in the Master Lock® Vault® – a FREE service from Master Lock that’s easy to use! The Master Lock Vault not only stores combinations, but other important documents such as passwords, tax documents, ID’s, etc.

Master Lock Serial Number List By Lars Kirmser

School faculty and fitness club staff members can retrieve multiple missing combination charts online by filling out and returning this Combination Chart Form via fax to 619.444.5677.