There's a recurring theme in ransomware defense: find the one thing the malware can't avoid doing, and watch for that. An attacker can obfuscate code, evade signatures, mimic benign behavior — but to be ransomware, the program has to encrypt the victim's files, and to encrypt files it has to perform cryptographic operations. Those operations are the irreducible core of the attack, and that makes them the most reliable thing to detect.
The grant US12511392B1, "Ransomware detection using cryptographic API call graph analysis" (issued December 30, 2025, assigned to Halcyon Tech, Inc.), zeroes in on exactly that. Its CPC classifications are tightly focused in the malware classes — G06F 21/566, G06F 21/54, and G06F 21/554 — describing detection grounded in how a program uses cryptography.
“An agent executing on a monitored computing device intercepts runtime execution data associated with a process by utilizing hooks into cryptographic application programming interfaces (APIs).”— U.S. Patent No. 12,511,392 source
The mechanism worth understanding is the call graph. When software encrypts data, it calls cryptographic functions in characteristic sequences — generating or importing keys, initializing ciphers, processing data in patterns. Ransomware's use of these calls has a recognizable shape: rapid, repeated encryption across many files, often with telltale key-handling. Building a graph of which cryptographic functions are called, in what order and at what scale, lets the system distinguish the cryptographic footprint of a ransomware attack from that of legitimate encryption.
For defenders, the practical takeaway is the durability of this signal. Detection based on the cryptographic behavior an attack cannot avoid is far more resilient than detection based on characteristics an attacker can change at will. The program can hide what it is; it cannot hide that it's encrypting everything in sight using the system's own cryptographic machinery.
That Halcyon — a company built specifically around anti-ransomware — holds this patent underscores how the specialist end of the market is converging on behavioral, crypto-aware detection. The discipline of ransomware defense has matured into a search for the unavoidable behaviors, and the cryptographic API call graph is one of the cleanest examples: the attack's defining act becomes the basis for catching it.