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Introduction
Digital forensics relies on bit‑exact, verifiable disk images to preserve evidence integrity. `ewfacquire` – part of the open‑source libewf project – creates forensic images in the Expert Witness Format (E01/EWF), the same standard used by EnCase. This guide walks through acquiring, verifying, and using EWF images across Linux and Windows, ensuring your evidence holds up in any investigation.
Learning Objectives
- Install and configure `ewfacquire` from the libewf suite on Linux and Windows.
- Acquire bit‑accurate disk images with compression, segmentation, and checksumming.
- Verify image integrity and mount EWF files for analysis with tools like Autopsy and The Sleuth Kit.
You Should Know
- Installing libewf and ewfacquire on Linux and Windows
`ewfacquire` is part of the `libewf` toolkit. On most Linux distributions it is available via package managers. On Windows, you can compile from source or use pre‑compiled binaries from the libewf project (e.g., via Cygwin or WSL). Below are verified installation commands.
Linux (Debian/Ubuntu):
sudo apt update sudo apt install libewf-tools
Linux (RHEL/CentOS/Fedora):
sudo yum install epel-release sudo yum install libewf-tools
Verify installation:
ewfacquire -V
Windows (using WSL – Windows Subsystem for Linux):
wsl --install -d Ubuntu wsl sudo apt update && sudo apt install libewf-tools
Alternatively, download pre‑compiled binaries from https://github.com/libyal/libewf/releases and add the folder to your PATH.
Step‑by‑step – what this does and how to use it:
These commands fetch and install the libewf utilities, including ewfacquire, ewfverify, and ewfmount. After installation, you can run `ewfacquire` from any terminal to start imaging.
2. Basic Disk Acquisition with ewfacquire
The simplest use of `ewfacquire` is to create an EWF image from a raw disk device (e.g., `/dev/sda` or a USB drive). The tool prompts interactively for metadata, compression, and segmentation settings. For scripting, command‑line flags can bypass prompts.
Basic interactive acquisition:
sudo ewfacquire /dev/sdb
You will be asked for:
- Case number, evidence number, examiner name, description.
- Compression level (none, fast, best).
- Segment size (default 1 GiB).
- Output directory and filename.
Non‑interactive (automated) acquisition:
sudo ewfacquire /dev/sdb -c fast -t case_drive1 -o /forensics/images -C 2024-001 -E examiner1 -d "Seized USB drive"
Step‑by‑step guide – what this does and how to use it:
1. Connect the suspect drive (ensure it is not mounted automatically – use `sudo umount /dev/sdb` first).
2. Run `ewfacquire` with the device path.
- Provide metadata when prompted – this becomes part of the EWF header.
- The tool reads every sector, compresses data on the fly, and writes to `.E01` (or
.E0x) segment files. - Upon completion, a checksum (MD5/SHA‑1) of the raw data is stored inside the image metadata.
3. Advanced Options: Compression, Segmentation, and Hashing
`ewfacquire` offers fine‑grained control to match investigation requirements. Use compression to save space, segmentation to fit evidence on DVDs or cloud storage, and multiple hash algorithms for integrity.
Common flags:
| Flag | Description | Example |
||-||
| `-c` | Compression level: none, `fast` (default), `best` | `-c best` |
| `-S` | Segment size in bytes (e.g., 1G, 650M) | `-S 2G` |
| `-l` | Log file path | `-l acquisition.log` |
| `-h` | Hash method: md5, sha1, `sha256` | `-h sha256` |
| `-m` | Additional metadata string | `-m “RAID0 volume”` |
Example – high‑compression, 2 GiB segments with SHA‑256:
sudo ewfacquire /dev/sdc -c best -S 2G -h sha256 -t evidence_drive -o /cases/2025-01/
Step‑by‑step – what this does and how to use it:
– `-c best` uses maximum gzip compression (slower but smallest files).
– `-S 2G` splits the image into 2 GiB segments (e.g., evidence_drive.E01, evidence_drive.E02).
– `-h sha256` computes a SHA‑256 hash of the entire acquired data for later verification.
– These options are critical when storing images on FAT32 volumes (max file size 4 GiB) or when network bandwidth is limited.
4. Verifying Image Integrity with ewfverify
After acquisition, you must confirm that the image is bit‑identical to the source and that no corruption occurred during imaging. `ewfverify` reads the EWF segments, recalculates checksums, and compares them to the stored values.
Command:
ewfverify evidence_drive.E01
Output interpretation:
– `Verified successfully` – image integrity is intact.
– `Verification failed` – data corruption or tampering detected. The tool reports which segment and sector is problematic.
Step‑by‑step – what this does and how to use it:
1. Run `ewfverify` against the first segment (.E01). It automatically finds all related segments.
2. The tool decompresses the image in a streaming fashion and recomputes the hash (MD5, SHA‑1, or SHA‑256 based on what was stored).
3. If hashes match, you can cryptographically prove that the image has not changed since acquisition.
4. Always run `ewfverify` before presenting evidence in court or after transferring the image to another storage location.
Script for automated verification of multiple images:
for img in /forensics/images/.E01; do echo "Verifying $img" ewfverify "$img" || echo "FAILED: $img" >> verify_errors.log done
5. Mounting and Analyzing EWF Images with ewfmount
To examine the contents of an EWF image without converting it, `ewfmount` creates a virtual read‑only mount point that exposes a raw (.raw) file. This raw representation can then be loop‑mounted or opened in forensic tools.
Mount the EWF image to a virtual raw file:
ewfmount evidence_drive.E01 /mnt/ewf_mount/
Now `/mnt/ewf_mount/ewf1` is a raw disk image.
Loop‑mount the raw image (Linux):
sudo losetup -f /mnt/ewf_mount/ewf1 sudo mount /dev/loop0 /mnt/analysis/
Step‑by‑step – what this does and how to use it:
1. `ewfmount` creates a FUSE filesystem that translates EWF read requests into raw sector reads.
2. The resulting file (e.g., ewf1) can be treated like any raw disk image – you can use `mmls` (The Sleuth Kit), Autopsy, or even `mount` it directly if it contains a standard filesystem.
3. To access individual partitions, use `kpartx -a /mnt/ewf_mount/ewf1` to create device mapper entries.
4. This method avoids extracting the entire image (which could be terabytes) and preserves the original EWF container.
Example – listing partitions with The Sleuth Kit:
ewfmount evidence.E01 /mnt/ewf/ mmls /mnt/ewf/ewf1
6. Windows‑Specific Usage and Integration with Autopsy
While `ewfacquire` is natively a Linux tool, Windows investigators can run it via WSL or use the libewf Windows binaries. The same command syntax applies. Autopsy, a popular GUI forensics platform, can directly read EWF images created by ewfacquire.
Using libewf binaries on native Windows (CMD or PowerShell):
ewfacquire.exe \.\PhysicalDrive2 -t D:\cases\drive_image -c fast
Note: Identify physical drives with `wmic diskdrive list brief` or
diskpart -> list disk.
Importing an EWF image into Autopsy:
1. Open Autopsy and create a new case.
- When adding a data source, choose “Disk Image or VM File”.
- Browse to the `.E01` file – Autopsy automatically reads segments and metadata.
- Proceed with analysis (file carving, keyword search, timeline).
Step‑by‑step – what this does and how to use it:
– On Windows, you can acquire a live system’s drive using the `\\.\PhysicalDriveN` syntax.
– After acquisition, copy the `.E01` and `.E0x` files to your forensic workstation.
– Autopsy’s EWF support leverages libewf, so it will verify integrity on import and display the original acquisition metadata.
– This workflow provides a free, open‑source alternative to EnCase for Windows‑based examiners.
7. Forensic Best Practices When Using ewfacquire
Maintaining chain of custody and forensic soundness is paramount. Follow these guidelines when using `ewfacquire` in real investigations.
Write‑block the source drive:
Use a hardware write‑blocker or software like `hdparm` (Linux) to prevent accidental writes:
sudo hdparm -r1 /dev/sdb set read-only
Log everything:
Redirect output and use the `-l` flag:
sudo ewfacquire /dev/sdb -l acquisition.log -t evidence -c fast 2>&1 | tee console.log
Compute external hashes before and after imaging:
Before imaging sudo dd if=/dev/sdb bs=1M | sha256sum > drive_original.hash After imaging (verify via ewfverify) ewfverify evidence.E01
Store metadata in a CSV manifest:
echo "Case,Examiner,Date,Device,Image,Hash" > manifest.csv echo "$CASE,$EXAM,$(date),$DEVICE,$IMAGE,$(ewfinfo evidence.E01 | grep SHA256)" >> manifest.csv
Step‑by‑step – what this does and how to use it:
– Write‑blocking ensures that even a mis‑typed command won’t alter evidence.
– Logging captures every sector’s status – crucial for court admissibility.
– External hashes provide a second verification layer independent of the EWF container.
– A manifest simplifies evidence management in multi‑disk cases.
What Undercode Say
- Key Takeaway 1: `ewfacquire` delivers enterprise‑grade forensic imaging without vendor lock‑in. Its support for compression, segmentation, and multiple hash algorithms makes it suitable for any investigation, from a single USB drive to petabytes of RAID storage.
- Key Takeaway 2: Integrity verification is non‑negotiable – always pair acquisition with `ewfverify` and maintain external logs. The libewf suite’s transparency allows anyone to audit the imaging process, strengthening the evidentiary chain.
The open‑source nature of `ewfacquire` has democratized digital forensics. Where commercial tools like EnCase cost thousands of dollars, investigators can now achieve the same EWF output for free. However, this power requires discipline: improper handling (e.g., not using a write‑blocker) can invalidate evidence. As cloud and encrypted drives become ubiquitous, `ewfacquire` must evolve to support live acquisition of remote block storage and integration with hardware security modules. Yet for traditional disk imaging, it remains a gold‑standard utility that every forensic analyst should master.
Prediction
As legal systems increasingly accept open‑source forensic tools, `ewfacquire` and libewf will see wider adoption in both public and private sector labs. Future versions may incorporate direct support for NVMe‑over‑TCP and cloud volume snapshots (e.g., AWS EBS). Simultaneously, anti‑forensic techniques like self‑encrypting drives will challenge acquisition – we predict a rise in `ewfacquire` extensions that interface with TPMs and key escrow services. Regardless, the core principles of bit‑exact imaging, metadata preservation, and checksum verification will remain the bedrock of digital evidence handling for the next decade.
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