<!-- Copyright (c) 2026 defconxt. All rights reserved. -->
<!-- Licensed under AGPL-3.0 — see LICENSE file for details. -->
---
name: analyzing-ransomware-decryption-feasibility
description: >-
  Analyze ransomware samples to determine decryption feasibility without
  paying ransom. Covers identification of ransomware families with known
  decryptors, cryptographic implementation weakness analysis, key recovery
  from memory dumps, partial file recovery techniques, and coordination
  with No More Ransom project resources.
domain: cybersecurity
subdomain: ransomware-defense
tags:
  - decryption-analysis
  - crypto-weakness
  - key-recovery
  - no-more-ransom
  - memory-forensics
  - file-recovery
  - ransomware-identification
  - decryptor-tools
version: '1.0'
author: defconxt
license: AGPL-3.0
metadata:
  mitre-attack: ["T1486"]
---

# Analyzing Ransomware Decryption Feasibility

## Overview

Not all ransomware encryption is unbreakable. Implementation flaws in
cryptographic routines, reused keys, weak PRNG seeding, and partial
encryption schemes create opportunities for data recovery without payment.
Additionally, law enforcement operations regularly seize decryption keys
and release free decryptors.

Before considering payment, exhaustively analyze decryption feasibility.
Approximately 30% of ransomware families have had free decryptors released.

## Prerequisites

| Tool | Purpose | Install |
|------|---------|---------|
| YARA | Ransomware identification | `pip install yara-python` |
| Volatility 3 | Memory forensics | `pip install volatility3` |
| photorec | File carving/recovery | `apt install testdisk` |
| CyberChef | Crypto analysis | Web app or local install |
| strings | Binary analysis | Built-in on Linux |
| xxd | Hex analysis | `apt install xxd` |

## Key Concepts

### Decryption Feasibility Decision Tree

```
Step 1: Identify ransomware family
  |-- Known family with decryptor -> Download and test
  |-- Known family, no decryptor -> Analyze crypto implementation
  +-- Unknown family -> Reverse engineer encryption routine

Step 2: Check for implementation weaknesses
  |-- Weak PRNG -> Key prediction possible
  |-- ECB mode -> Pattern preservation, partial recovery
  |-- Partial encryption -> Recover unencrypted portions
  +-- Key in memory -> Memory dump analysis

Step 3: Attempt recovery
  |-- Free decryptor available -> nomoreransom.org
  |-- Key extracted -> Build custom decryptor
  |-- File carving -> Recover unencrypted slack/temp files
  +-- No path -> Document for law enforcement coordination
```

### Common Cryptographic Weaknesses

| Weakness | Exploitability | Families Affected |
|----------|---------------|-------------------|
| Weak PRNG seeding | High | Older variants, amateur ransomware |
| ECB encryption mode | Medium | Some Dharma variants |
| Static/hardcoded keys | High | WannaCry (partial), Petya |
| Key stored in memory | High (if dumped early) | Many families pre-wipe |
| Partial file encryption | Medium | LockBit (header-only mode) |

## Workflow

### Step 1 — Identify Ransomware Family

```bash
# Analyze encrypted file headers for family identification
xxd -l 256 encrypted_file.locked | head -20

# Check ransom note for family indicators
cat README_RANSOM.txt 2>/dev/null | head -20

# YARA scan for ransomware identification
yara -r ransomware_rules.yar /path/to/sample 2>/dev/null

# String analysis of ransomware binary
strings -n 8 ransomware_sample.exe 2>/dev/null | \
  grep -iE "bitcoin|ransom|wallet|decrypt|onion|tor|encrypt" | sort -u

# Upload to ID Ransomware for identification
echo "Upload sample to: https://id-ransomware.malwarehunterteam.com/"
```

### Step 2 — Check for Available Decryptors

```bash
echo "=== NO MORE RANSOM DECRYPTOR CHECK ==="
echo "Portal: https://www.nomoreransom.org/en/decryption-tools.html"
echo ""
echo "Known decryptable families (partial list):"
echo "  - GandCrab (all versions)"
echo "  - REvil/Sodinokibi (some versions)"
echo "  - Shade/Troldesh"
echo "  - Jigsaw"
echo "  - Dharma (some variants)"
echo "  - MegaCortex"
echo ""
echo "Emsisoft: https://www.emsisoft.com/en/ransomware-decryption/"
echo "Kaspersky: https://noransom.kaspersky.com/"
```

### Step 3 — Memory Forensics for Key Recovery

```bash
# Capture memory dump (if system still running)
dd if=/proc/kcore of=/evidence/memory.dmp bs=1M 2>/dev/null

# Volatility 3: Search for encryption keys in memory
vol -f /evidence/memory.dmp windows.filescan | grep -iE '\.key$|\.pem$'

# Search for RSA key material
strings /evidence/memory.dmp | grep -E "BEGIN (RSA |)PRIVATE KEY"

# Search for AES key patterns in memory
vol -f /evidence/memory.dmp windows.vadinfo --pid <RANSOMWARE_PID>
```

### Step 4 — File Carving and Partial Recovery

```bash
# PhotoRec: Carve deleted original files
photorec /dev/sda2 /d /evidence/carved/

# Check VSS for pre-encryption snapshots (if not deleted)
vssadmin list shadows 2>/dev/null

# Check for partially encrypted files (header-only encryption)
for f in *.locked; do
  tail -c +4097 "$f" > "/evidence/partial_${f%.locked}" 2>/dev/null
done
echo "Partial recovery attempted — check /evidence/partial_*"
```

## Detection

```yaml
title: Ransomware Decryption Feasibility Detection
id: 9c401d74-d773-439f-ae3b-7bba2d7fa571
status: experimental
description: Detects suspicious activity related to analyzing ransomware decryption feasibility techniques in ransomware defense context
logsource:
  category: file_change
  product: windows
detection:
  selection:
    TargetFilename: "*suspicious*"
  condition: selection
level: critical
tags:
  - attack.t1486
  - attack.impact
falsepositives:
  - Backup software performing scheduled file encryption operations
```

## Verification

- [ ] Ransomware family positively identified via multiple methods
- [ ] No More Ransom and vendor decryptor catalogs checked
- [ ] Memory dump acquired and analyzed for key material
- [ ] File carving attempted for original file recovery
- [ ] Partial encryption analysis completed for header-only variants
- [ ] Findings documented for law enforcement and insurance

## References

- No More Ransom Project: nomoreransom.org
- MITRE ATT&CK T1486: Data Encrypted for Impact
- Europol EC3: Ransomware Decryption Resources
- CISA: Ransomware Guide (Recovery Section)
- Volatility Foundation: Memory Forensics Framework
