A science librarian once told me that all the literature on biology, chemistry and other sciences more than five years old could be thrown out and it wouldn’t make any difference. She said it was only mathematicians and some physicists who cared about anything older. With science and technology advancing so rapidly that anything old enough to have a little dust on it is obsolete, does history really matter?

In my field, cryptology—the study of codes and ciphers—it definitely does.

Whereas encryption algorithms are continually being improved, upgrades are not always automatic. There are plenty of old systems still in use. And when it comes to ciphers used by bad guys of all sorts, old can mean centuries. Some criminals believe the National Security Agency can break all of the current systems so they fall back on older, weaker ciphers. This is ridiculous for a number of reasons—not the least of which, it is the FBI, not the NSA, that American citizens engaged in criminal activities need to worry about. In any case, the FBI’s Cryptanalysis and Racketeering Records Unit (CRRU) regularly sees Vigenère ciphers, for example, despite the fact this method goes back to the 16th century and a method for deciphering it was published in 1863. Of course, criminals make all sorts of mistakes, and failing to learn from history is among them.

Criminals don’t just fall back on older ciphers out of paranoia; in some cases they don’t have access to the technology needed to keep their encryption up to date. A great example of this is law-breakers serving time. About 80 percent of the CRRU’s workload consists of prison ciphers. Imprisoned gang members are often still running operations and giving orders. Their resources are limited, but anyone with pencil and paper can write in cipher. The Aryan Brotherhood is the source of endless FBI headaches in this regard. One doesn’t need to belong to a gang to hide information with codes or ciphers, however. There are numerous serial killers who carried out their crimes without accomplices but nonetheless wrote in cipher, sometimes to newspapers and sometimes in their personal journals. Examples include Zodiac, a Zodiac copycat killer in 1990s New York City, the Unabomber, the mass murderer known as BTK (Bind, Torture, Kill) and more. Old paper-and-pencil-type ciphers are still important.

It’s common for a person enciphering a message to be overconfident as to the level of protection thus acquired. This is nothing new. During World War II some Nazis realized the Enigma cipher machines on which they relied so heavily could theoretically be cracked, but they didn’t think anyone would make the intense effort required to actually do it. The fact mathematicians from Poland, England and the U.S. did is now well known—among other things, it was the plot of the 2014 movie The Imitation Game—but the story was kept secret until the 1970s. The people who were in the know (more than 10,000 of them) kept their mouths shut for decades. Meanwhile various versions of the Enigma machine and other similar devices continued to be used—in some cases on into the 1990s. Once again, “historical” ciphers stayed relevant.

In the digital world and the throwaway society we’ve become, where only the latest and greatest devices and technology will suffice, it can be easy to think of everything in the same way. But codes and ciphers have a long track record of being recycled, and professionals must realize that what’s old is new again.

Yes, technology is always changing. But there are hundreds of examples of centuries-old ciphers that still remain unsolved to this day. They illustrate that newer is not always better as well as the importance of thinking holistically when approaching the mysteries that remain before us.