File Hider

Hide any file inside another file (JPEG, PNG, MP3, PDF). Creates polyglot files that open normally but contain hidden payloads. AES-256 encrypted.

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Configure

Encode

Drop carrier file or click to browse

JPEG, PNG, MP3, PDF, or any file (max 500MB)

Try the demo instantly — no upload needed

Loads sample.png (1×1 PNG carrier) + hello.txt (the secret).

jpeg

png

mp3

pdf

How to Hide a File Inside Another File (4 steps)

Upload a carrier file (JPEG, PNG, MP3, PDF, or any file)
Add the file or files you want to hide inside it
Pick a method (EOF append for everything · PNG chunk injection for hardened CTFs)
Optionally encrypt with AES-256, choose a redundancy level, or set a custom marker
Click Encode — download a polyglot file that opens normally yet carries your payload

File Hiding Methods — How This Tool Works

Method	Technique	Advantage	Best For
EOF Append	Adds payload after the carrier's natural end-of-file marker	Carrier opens normally in any viewer · unlimited capacity	Default — JPEG/PNG/MP3/PDF/anything
PNG Chunk Injection (stEG)	Inserts payload as a custom 'stEG' chunk before IEND with a valid CRC32	Survives some PNG re-saves · invisible to file-size checks	Hardened CTF challenges, archival images
Multi-file ZIP	JSZip-bundles multiple input files before embedding	Same wire format · transparent to the user	Hiding 2+ files at once
AES-256-GCM	Encrypts the payload before appending	Wrong password silently rejected · plausible deniability	Encrypted exfil / CTF challenges
Reed-Solomon Redundancy	Wraps the payload in shard-based redundancy (RS-10/20/30)	Survives 10–30% trailing-data corruption	Unreliable transfer / archival storage
EP_STEGO marker	8-byte magic header + 1B flags + 4B BE length	Decoder auto-locates and extracts	Round-trip with this decoder

Format Structure — Where Your Payload Sits

JPEG

[FF D8] [APP markers] [Image data...] [FF D9 ← EOI]
                                        └─────► [EP_STEGO][flags][len][payload...]
                                              ↑ Image viewers stop at FF D9
                                                Hidden payload begins here

Description

JPEG decoders stop at the FF D9 EOI marker — every byte after is ignored.

Parser behavior

Standard libraries (libjpeg, browser) terminate after EOI.

Detectable by

binwalk, hex editor, file size delta

Survives

Direct copy, email, Discord, Drive, Dropbox

Destroyed by

JPEG re-encode (Instagram, WhatsApp, Twitter)

PNG

[89 50 4E 47 0D 0A 1A 0A] [IHDR] [IDAT...] [IEND]
                                                    ↑
                               EOF append → [EP_STEGO][flags][len][payload]
                               stEG inject → [len][stEG][payload][CRC32] before IEND

Description

PNG ignores unknown chunk types. Both EOF append and chunk injection survive lossless copies.

Parser behavior

Decoders walk chunks until IEND. Unknown chunks are silently skipped.

Detectable by

pngcheck (chunk audit), hex editor

Survives

Direct copy, Discord (PNG), email, Drive, Dropbox

Destroyed by

Forced PNG re-save with chunk-stripping flags

MP3

[ID3 header] [Frame 1] [Frame 2] ... [Frame N]
                                              └────► [EP_STEGO][flags][len][payload]
                                                  ↑ Players read declared frame count

Description

MP3 players read declared audio frames and stop. Trailing data is ignored.

Parser behavior

ffplay/foobar/iTunes terminate on the last audio frame.

Detectable by

binwalk, file size analysis

Survives

Direct copy, Discord, email, Drive

Destroyed by

Re-encoding (lame/ffmpeg with -y), streaming services

PDF

[%PDF-1.x] [Object stream...] [xref] [trailer] [%%EOF]
                                                     └────► [EP_STEGO][flags][len][payload]
                                                          ↑ Readers terminate at %%EOF

Description

PDF spec mandates readers stop at the last %%EOF. Trailing data is invisible.

Parser behavior

Adobe Reader, browser PDF.js, Preview all stop at %%EOF.

Detectable by

binwalk, file size analysis, PDF byte audit

Survives

Direct copy, email, Drive, Dropbox

Destroyed by

PDF rewrite tools (qpdf --object-streams=disable, etc.)

Generic

[ ... carrier bytes ... ] [EP_STEGO][flags][len][payload...]
                                   ↑ No native viewer — append at end of buffer

Description

For unknown formats, the marker + payload are appended at the end of the buffer.

Parser behavior

Behaviour depends on the consumer — many parsers ignore trailing data.

Detectable by

binwalk, signature scan, hex editor

Survives

Any byte-identical transport

Destroyed by

Any transformation that rewrites the file

Detection Resistance & Platform Survival

How each method is detected

EOF Append (any format)

Detectable by: binwalk -e, file size comparison, hex editor

Not detectable by: image viewers, audio players, PDF readers, casual inspection

Survives byte-identical copies · destroyed by re-encoding

PNG Chunk Injection (stEG)

Detectable by: pngcheck, chunk-aware analyzers

Not detectable by: standard image viewers, naive file-size analysis, binwalk default scan

Survives most lossless image-processing pipelines

AES-256-GCM payload

Detectable by: entropy analysis (high entropy = likely encrypted)

Not detectable by: binwalk -e (cannot extract without password), string scans

Cipher integrity is verified via GCM auth tag — corruption = decode fail

Reed-Solomon (RS-10/20/30)

Detectable by: entropy analysis, blob-size signature

Not detectable by: binwalk, casual hex inspection

Recovers from 10–30% trailing-data corruption (depending on tier)

Platform survival — does the payload arrive intact?

Platform	What it does	Survival
Direct download / USB	No processing	Survives
Discord (PNG)	Lossless copy	Survives
Discord (JPEG)	May re-encode	Destroyed
Email attachment	No re-encoding	Survives
Instagram (JPEG)	Re-encodes JPEG	Destroyed
WhatsApp photos	Re-encodes	Destroyed
Twitter / X (JPEG)	Re-encodes	Destroyed
Google Drive / Dropbox	No re-encoding	Survives

Rule of thumb: use PNG for anything shared online · JPEG only for direct file transfer (USB, email, Drive).

Frequently Asked Questions

What file types can I use as a carrier?

JPEG, PNG, MP3, PDF, or any file. Image/audio/PDF carriers stay viewable in their normal apps because those parsers stop at the format's own EOF marker. Generic carriers also work — they just won't have a 'nice' viewer.

Will the carrier still open normally after embedding?

Yes. Image viewers stop reading at FF D9 (JPEG) or IEND (PNG); MP3 players stop at the last audio frame; PDF readers stop at %%EOF. The appended payload sits past those markers and is invisible to those parsers.

What does the Carrier Integrity Test do?

After embedding, the tool re-parses the output and runs format-specific checks (JPEG SOI/EOI, PNG signature + CRC32 per chunk, PDF %%EOF, MP3 frame sync). It tells you immediately whether the carrier still opens normally — no tool currently does this.

What's the Polyglot Validator?

For images, the validator decodes the output through the browser's ImageBitmap (the same code path used by ⟨img⟩) and scans for a ZIP signature in the trailing data. A green light means the file is genuinely valid as both formats simultaneously.

Can I hide more than one file?

Yes. Use the 'Add another file' button in the Configure step — multiple files are zipped automatically before embedding, and the decoder unpacks them on the other side.

What is PNG Chunk Injection (stEG) and when should I use it?

Instead of appending after IEND, the payload is inserted as a custom 'stEG' chunk inside the PNG with a valid CRC32. Image viewers ignore unknown chunks (PNG spec) so the image still renders, but the file size scan and binwalk's basic mode won't flag trailing garbage. Best for CTF challenges where standard tools should miss the payload.

What does Reed-Solomon redundancy add?

RS-10 / RS-20 / RS-30 wrap the payload in error-correction shards so the hidden file can be recovered even if 10/20/30% of the trailing data is corrupted (partial download, transit error, etc.). Overhead: ~11/25/43%. Recommended: RS-20.

Is my file uploaded anywhere?

Never. Everything runs in this browser tab using ArrayBuffer manipulation, JSZip, and the Web Crypto API. Files don't leave the device — encoding heavy lifting runs in a WebWorker, and large outputs stream directly to disk via StreamSaver.

How is the hidden payload found again?

An 8-byte magic header ("EP_STEGO\0") + 1 flags byte + 4 length bytes are appended just before the payload. The decoder scans for that marker and extracts exactly the declared number of bytes.