メニュー
Create forensically sound bit-for-bit disk images using dd and dcfldd while preserving evidence integrity through hash verification.
Codex または Claude でインストール この Prompt をコピーして Codex、Claude、または他のアシスタントに貼り付けると、Skill ページを確認してインストールできます。
SOC 職業分類に基づく
| name | acquiring-disk-image-with-dd-and-dcfldd |
| description | Create forensically sound bit-for-bit disk images using dd and dcfldd while preserving evidence integrity through hash verification. |
| license | Apache-2.0 |
| metadata | {"domain":"cybersecurity","subdomain":"digital-forensics","tags":["forensics","disk-imaging","evidence-acquisition","dd","dcfldd","hash-verification"],"version":"1.0","author":"mahipal","nist_csf":["RS.AN-01","RS.AN-03","DE.AE-02","RS.MA-01"],"mitre_attack":["T1006","T1005","T1025","T1074.001"]} |
dd (pre-installed on all Linux systems) or dcfldd (enhanced forensic version)sha256sum, md5sum)# List all connected block devices to identify the target
lsblk -o NAME,SIZE,TYPE,MOUNTPOINT,MODEL
# Verify the device details
fdisk -l /dev/sdb
# Enable software write-blocking (if no hardware blocker)
blockdev --setro /dev/sdb
# Verify read-only status
blockdev --getro /dev/sdb
# Output: 1 (means read-only is enabled)
# Alternatively, use udev rules for persistent write-blocking
echo 'SUBSYSTEM=="block", ATTRS{serial}=="WD-WCAV5H861234", ATTR{ro}="1"' > /etc/udev/rules.d/99-writeblock.rules
udevadm control --reload-rules
# Create case directory structure
mkdir -p /cases/case-2024-001/{images,hashes,logs,notes}
# Document source drive information
hdparm -I /dev/sdb > /cases/case-2024-001/notes/source_drive_info.txt
# Record the serial number and model
smartctl -i /dev/sdb >> /cases/case-2024-001/notes/source_drive_info.txt
# Pre-hash the source device
sha256sum /dev/sdb | tee /cases/case-2024-001/hashes/source_hash_before.txt
# Basic dd acquisition with progress and error handling
dd if=/dev/sdb of=/cases/case-2024-001/images/evidence.dd \
bs=4096 \
conv=noerror,sync \
status=progress 2>&1 | tee /cases/case-2024-001/logs/dd_acquisition.log
# For compressed images to save space
dd if=/dev/sdb bs=4096 conv=noerror,sync status=progress | \
gzip -c > /cases/case-2024-001/images/evidence.dd.gz
# Using dd with a specific count for partial acquisition
dd if=/dev/sdb of=/cases/case-2024-001/images/first_1gb.dd \
bs=1M count=1024 status=progress
# Install dcfldd if not present
apt-get install dcfldd
# Acquire image with built-in hashing and split output
dcfldd if=/dev/sdb \
of=/cases/case-2024-001/images/evidence.dd \
hash=sha256,md5 \
hashwindow=1G \
hashlog=/cases/case-2024-001/hashes/acquisition_hashes.txt \
bs=4096 \
conv=noerror,sync \
errlog=/cases/case-2024-001/logs/dcfldd_errors.log
# Split large images into manageable segments
dcfldd if=/dev/sdb \
of=/cases/case-2024-001/images/evidence.dd \
hash=sha256 \
hashlog=/cases/case-2024-001/hashes/split_hashes.txt \
bs=4096 \
split=2G \
splitformat=aa
# Acquire with verification pass
dcfldd if=/dev/sdb \
of=/cases/case-2024-001/images/evidence.dd \
hash=sha256 \
hashlog=/cases/case-2024-001/hashes/verification.txt \
vf=/cases/case-2024-001/images/evidence.dd \
verifylog=/cases/case-2024-001/logs/verify.log
# Hash the acquired image
sha256sum /cases/case-2024-001/images/evidence.dd | \
tee /cases/case-2024-001/hashes/image_hash.txt
# Compare source and image hashes
diff <(sha256sum /dev/sdb | awk '{print $1}') \
<(sha256sum /cases/case-2024-001/images/evidence.dd | awk '{print $1}')
# If using split images, verify each segment
sha256sum /cases/case-2024-001/images/evidence.dd.* | \
tee /cases/case-2024-001/hashes/split_image_hashes.txt
# Re-hash source to confirm no changes occurred
sha256sum /dev/sdb | tee /cases/case-2024-001/hashes/source_hash_after.txt
diff /cases/case-2024-001/hashes/source_hash_before.txt \
/cases/case-2024-001/hashes/source_hash_after.txt
# Generate acquisition report
cat << 'EOF' > /cases/case-2024-001/notes/acquisition_report.txt
DISK IMAGE ACQUISITION REPORT
==============================
Case Number: 2024-001
Date/Time: $(date -u +"%Y-%m-%d %H:%M:%S UTC")
Examiner: [Name]
Source Device: /dev/sdb
Model: [from hdparm output]
Serial: [from hdparm output]
Size: [from fdisk output]
Acquisition Tool: dcfldd v1.9.1
Block Size: 4096
Write Blocker: [Hardware/Software model]
Image File: evidence.dd
Image Hash (SHA-256): [from hash file]
Source Hash (SHA-256): [from hash file]
Hash Match: YES/NO
Errors During Acquisition: [from error log]
EOF
# Compress logs for archival
tar -czf /cases/case-2024-001/acquisition_package.tar.gz \
/cases/case-2024-001/hashes/ \
/cases/case-2024-001/logs/ \
/cases/case-2024-001/notes/
| Concept | Description |
|---|---|
| Bit-for-bit copy | Exact replica of source including unallocated space and slack space |
| Write blocker | Hardware or software mechanism preventing writes to evidence media |
| Hash verification | Cryptographic hash comparing source and image to prove integrity |
| Block size (bs) | Transfer chunk size affecting speed; 4096 or 64K typical for forensics |
| conv=noerror,sync | Continue on read errors and pad with zeros to maintain offset alignment |
| Chain of custody | Documented trail proving evidence has not been tampered with |
| Split imaging | Breaking large images into smaller files for storage and transport |
| Raw/dd format | Bit-for-bit image format without metadata container overhead |
| Tool | Purpose |
|---|---|
| dd | Standard Unix disk duplication utility for raw imaging |
| dcfldd | DoD Computer Forensics Laboratory enhanced version of dd with hashing |
| dc3dd | Another forensic dd variant from the DoD Cyber Crime Center |
| sha256sum | SHA-256 hash calculation for integrity verification |
| blockdev | Linux command to set block device read-only mode |
| hdparm | Drive identification and parameter reporting |
| smartctl | S.M.A.R.T. data retrieval for drive health and identification |
| lsblk | Block device enumeration and identification |
Scenario 1: Acquiring a Suspect Laptop Hard Drive
Connect the drive via a Tableau T35u hardware write-blocker, identify as /dev/sdb, use dcfldd with SHA-256 hashing, split into 4GB segments for DVD archival, verify hashes match, document in case notes.
Scenario 2: Imaging a USB Flash Drive from a Compromised Workstation
Use software write-blocking with blockdev --setro, acquire with dcfldd including MD5 and SHA-256 dual hashing, image is small enough for single file, verify and store on encrypted case drive.
Scenario 3: Remote Acquisition Over Network
Use dd piped through netcat or ssh for remote acquisition: ssh root@remote "dd if=/dev/sda bs=4096" | dd of=remote_image.dd bs=4096, hash both ends independently to verify transfer integrity.
Scenario 4: Acquiring from a Failing Drive
Use ddrescue first to recover readable sectors, then use dd with conv=noerror,sync to fill gaps with zeros, document which sectors were unreadable in the error log.
Acquisition Summary:
Source: /dev/sdb (500GB Western Digital WD5000AAKX)
Destination: /cases/case-2024-001/images/evidence.dd
Tool: dcfldd 1.9.1
Block Size: 4096 bytes
Duration: 2h 15m 32s
Bytes Copied: 500,107,862,016
Errors: 0 bad sectors
Source SHA-256: a3f2b8c9d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1
Image SHA-256: a3f2b8c9d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1
Verification: PASSED - Hashes match
Detect dangerous ACL misconfigurations in Active Directory using ldap3 to identify GenericAll, WriteDACL, and WriteOwner abuse paths
Perform static analysis of Android APK malware samples using apktool for decompilation, jadx for Java source recovery, and androguard for permission analysis, manifest inspection, and suspicious API call detection.
Parses API Gateway access logs (AWS API Gateway, Kong, Nginx) to detect BOLA/IDOR attacks, rate limit bypass, credential scanning, and injection attempts. Uses pandas for statistical analysis of request patterns and anomaly detection. Use when investigating API abuse or building API-specific threat detection rules.
Analyze advanced persistent threat (APT) group techniques using MITRE ATT&CK Navigator to create layered heatmaps of adversary TTPs for detection gap analysis and threat-informed defense.
Queries Azure Monitor activity logs and sign-in logs via azure-monitor-query to detect suspicious administrative operations, impossible travel, privilege escalation, and resource modifications. Builds KQL queries for threat hunting in Azure environments. Use when investigating suspicious Azure tenant activity or building cloud SIEM detections.
Analyzes bootkit and advanced rootkit malware that infects the Master Boot Record (MBR), Volume Boot Record (VBR), or UEFI firmware to gain persistence below the operating system. Covers boot sector analysis, UEFI module inspection, and anti-rootkit detection techniques. Activates for requests involving bootkit analysis, MBR malware investigation, UEFI persistence analysis, or pre-OS malware detection.