Encryption is the process of converting readable data into an unreadable form using a mathematical algorithm and a key, so that only someone with the correct key can convert it back. It is a core tool for protecting data, and it is also the mechanism ransomware abuses to hold data hostage.
What encryption is
Encryption is one of the foundational tools of all of modern computing security. At its simplest, it takes readable information, called plaintext, and scrambles it into an unreadable form, called ciphertext, using a mathematical algorithm and a secret value called a key. Without the correct key, the ciphertext is meaningless noise. With the key, it can be converted back into the original readable data. This lets information be stored or sent in a form that is useless to anyone who intercepts it but perfectly usable by its intended owner.
Encryption protects data in two main situations. Data at rest is encrypted while stored on a disk or in a database, so a stolen hard drive or database is unreadable. Data in transit is encrypted while moving across a network, which is what the padlock in a web browser represents, so that information sent over the internet cannot be read by anyone eavesdropping on the connection. In both cases the goal is the same: make the data readable only to those who are supposed to read it.
The same tool, used for good and for harm
The striking thing about encryption in the context of ransomware is that it is not a malicious technology being misused in some exotic way. It is exactly the same strong, legitimate encryption that protects banking, healthcare, and government data every day, simply pointed in the opposite direction. Where a defender uses encryption to make data unreadable to attackers, ransomware uses encryption to make data unreadable to its rightful owner.
This is what makes ransomware so hard to simply undo. Modern encryption is designed to be effectively impossible to reverse without the key, that is the entire point, so when ransomware encrypts an organization's files, there is genuinely no practical way to decrypt them by brute force. The attacker holds the only key, which is precisely the leverage behind the ransom demand. Occasionally researchers find a flaw in a particular ransomware's implementation that allows free decryption, but a competently built strain cannot be broken, which is why organizations cannot rely on cracking the encryption as a recovery strategy.
How ransomware uses encryption in an attack
In the final stage of a ransomware attack, after the attacker has explored the network and stolen data, they deploy the encryption payload across as many systems as they can reach. The malware systematically encrypts files, often prioritizing the most valuable data and the systems most critical to operations, and typically deletes the original readable copies and any accessible backups as it goes. When it finishes, the organization is locked out of its own data, and a ransom note explains how to pay for the key.
A technical detail worth knowing is that this bulk encryption is actually detectable while it happens, which is important for defense. Encrypting large numbers of files in a short time produces a distinctive signature: a sudden spike in files being modified and a sharp rise in the randomness, or entropy, of file contents as readable data becomes scrambled. A defense watching for this behavior can catch mass encryption in its first moments, which is one of the clearest behavioral signals of ransomware in action.
Encryption, backups, and recovery
Because the encryption itself cannot be reversed without the key, the realistic defense against the encryption half of ransomware is not to break it but to make it irrelevant. If an organization holds a clean, unencrypted copy of its data that the attacker could not reach, immutable and air-gapped backups, then it does not matter that the production copies are locked. It can simply restore from the clean copy and ignore the demand for the key. The attacker's encryption is only powerful if it is the only copy; with a protected backup, it becomes a nuisance rather than a catastrophe.
This is why strong encryption cuts both ways in a resilient strategy. Used defensively, it protects data at rest and in transit so that even if attackers steal it, it is far less useful to them, which blunts the data-theft half of a double-extortion attack. Used by the attacker, it is defeated not by cryptography but by recovery, by having a clean copy safely out of reach. Understanding encryption as a neutral, powerful tool, decisive for whichever side controls the key, clarifies both why ransomware works and why protected backups are the answer to it.
Why you cannot just decrypt your way out
A question victims often ask in the first hours of an attack is whether the encrypted files can simply be cracked, broken open without paying the attacker. It is a natural hope, but with competently built ransomware the honest answer is no. Modern encryption algorithms are the product of decades of public scrutiny and are designed so that, without the key, there is no shortcut: the only way to find the key by brute force would take longer than the age of the universe with any computing power that exists. That strength is exactly why we trust the same algorithms to protect banking and medical data, and it is exactly why it cannot be undone when turned against you.
There are narrow exceptions that are worth knowing but not relying on. Occasionally security researchers or law enforcement find a flaw in a specific ransomware strain's implementation, how it generated or stored its keys, and release a free decryption tool, and initiatives exist to collect such tools for victims. Sometimes keys are recovered when an operation is taken down. But these are opportunistic and strain-specific; a victim cannot count on a free decryptor existing for the ransomware that hit them, and the best-run ransomware operations make no such mistakes. This is the fundamental reason recovery strategy centers on protected backups rather than on defeating the encryption: you plan to make the attacker's key irrelevant, not to break it.
See also
Sources
Definitions are drawn from the cited sources and were current as of publication. Content was rephrased for compliance with source licensing.