Malware Analysis Series

Akira encrypter: hunting notes

Data sources: Sysmon (1, 11), EDR file and rename telemetry, Windows Application log (Restart Manager).

Signal Source Why it fires
Bursts of *.arika creates, then the same paths renamed to *.akira Sysmon 11 / EDR rename telemetry Each file first gets a 532-byte .arika journal, then a FileRenameInfo rename to .akira
akira_readme.txt created in many folders within seconds file events One note per traversed folder
New Log-??-??-????-??-??-??.txt next to an unknown executable file events Built-in operator log in the working directory
.akira file = original size + 512 bytes; the last 512 bytes are high-entropy file triage RSA-4096 footer holding the wrapped per-file keys
Leftover *.arika of exactly 532 bytes file triage Interrupted encryption: still holds the RSA blob and progress mark

Ordered API anchor (EDR / ETW, one unsigned process):

  1. WTSEnumerateProcessesW;
  2. COM WbemLocator → Win32_Process.Create with a hidden Win32_ProcessStartup;
  3. many RmStartSession / RmShutdown(RmForceShutdown) pairs;
  4. overlapped ReadFile/WriteFile at the same offsets;
  5. SetFileInformationByHandle(FileRenameInfo) to *.akira.

Response note: do not reboot an encrypted host. Run collect_clock_and_times.ps1 first. The clock-to-uptime offset from the same boot is what makes key recovery practical.