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Expert Witness Disk Image (file extension .E01) is the original bitstream variant of the Expert Witness File/Compression Format (EWF), a family of digital-forensics container formats used to store sector-by-sector copies of storage media together with metadata and fixity information. The format originated with Guidance Software's Expert Witness/EnCase tools and is now widely supported by forensic software and libraries.[1][2]
Overview
E01 images belong to the broader EWF family of disk-image formats. An EWF image can capture the contents and structure of a device (e.g., hard drive, optical disc, removable media) and embeds case/acquisition metadata and integrity checks. EWF organizes data into sections with per-section fixity (commonly Adler-32) and may apply compression and multi-file segmentation for large acquisitions.[2] The E01 subtype is the first EnCase bitstream format; its counterpart L01 is the original EnCase logical-evidence container.[1][3]
Structure and features
According to the Library of Congress summary (based on Joachim Metz's reverse-engineered specification), E01 files comprise 13 named sections (e.g., Header, Table, Data, Session, Hash, Digest) derived from earlier SMART/EWF designs and extended by EnCase.[1] Family-level characteristics include:
**Fixity:** section-level checksums (often Adler-32) and optional whole-image message digests (e.g., MD5/SHA-1) recorded in metadata;[2]
**Compression:** typically deflate (per RFC 1951) to reduce size;[2]
**Segmentation:** large images may be split into a sequence with incrementing extensions (e.g., ``image.E01``, ``image.E02`` … ``image.E99``, then ``image.EAA``, ``image.EAB``, etc.);[1]
**Metadata:** case identifiers, examiner/acquisition details, and tool provenance, facilitating audit trails and chain-of-custody.[2]
File identification
The LoC entry lists E01’s common signature and naming conventions, including the magic number beginning with ASCII EVF and the segmented filename pattern noted above.[1]
Variants and versioning
EWF encompasses several related subtypes:
**SMART S01** (ASR Data; earliest published spec).
**EnCase E01** (bitstream) and **L01** (logical evidence).
**EWF2** formats introduced with EnCase 7: **Ex01** (bitstream) and **Lx01** (logical). These “version 2” containers expand sectioning and add features such as native encryption and revised compression behavior in EnCase 7.x.[4][5][6][7]
For Ex01/Lx01, see also the LoC subtype pages and EWF family notes.[8][9]
Tool support and interoperability
E01/EWF is supported by commercial suites (e.g., OpenText EnCase) and by open-source tools via the libewf library (reading/writing E01; read support for some logical variants), enabling use with analysis frameworks such as The Sleuth Kit and distributions like BitCurator and Kali.[10][11][12][2]
History and context
EWF emerged from late-1990s forensic imaging workflows (Guidance/EnCase and ASR Data/SMART). Public reverse-engineering and documentation efforts (notably by Joachim Metz) produced an open library (libewf) and detailed specifications used by many third-party tools.[2] Open alternatives such as the Advanced Forensic Format (AFF) were proposed to provide extensible, openly specified containers for disk images and metadata.[13]
