The present disclosure describes systems and methods for detection and mitigation of malicious encryption. A security agent on an infected computing device may monitor data writes to disk, memory, or network transmission buffers for strings that may represent encryption keys or moduli. The security agent may apply one or more techniques to decode and parse the string to either identify or extract the keys, or rule out the string as containing an encryption key or modulus. If a key is identified, or its presence cannot be excluded, then the security agent may generate an alert and take mitigation actions.