[WHAT IS AN ENCRYPTED FILE?]
A file whose contents have been scrambled so that only someone with the key can read them.
An encrypted file is an ordinary file whose contents have been transformed by a cipher. The bytes on disk no longer resemble the original document, image or spreadsheet, and they cannot be turned back without the correct key. Anyone who copies the file gets the scrambled version and learns nothing from it.
The important part is that this is reversible only with the key. That single property is what separates encryption from every other transformation a file can undergo.
[WHAT AN ENCRYPTED FILE LOOKS LIKE INSIDE]
Open an ordinary PDF in a text editor and you see %PDF-1.7 at the top, some readable metadata, and fragments of text. Open the encrypted version and you see uniform noise from the first byte to the last.
This is the practical test for whether a file is encrypted: high entropy with no readable strings anywhere. Most file formats leave recognisable traces — a magic number at the start, metadata at the end, embedded text in the middle. Encrypted data has none, because a good cipher produces output statistically indistinguishable from random.
One exception is worth knowing: many encryption formats keep a small plaintext header, so the first few bytes may be readable even though everything after them is not. That header records which algorithm was used and other parameters a decrypter needs before it has a key. Our own format does exactly this — see the .enc specification.
[ENCRYPTION IS NOT ENCODING, COMPRESSION OR HASHING]
These four get confused constantly, and the confusion leads people to look for tools that cannot exist. The distinction is about who can reverse the process.
| Process | Reversible? | Purpose |
|---|---|---|
| Encryption (AES, ChaCha20) | Only with the key | Confidentiality |
| Encoding (base64, hex) | By anyone | Safe transport of binary data through text channels |
| Compression (ZIP, gzip) | By anyone | Smaller size |
| Hashing (SHA-256, MD5) | Never — one-way by design | Integrity checking, password storage |
Base64 in particular looks like encryption to the untrained eye, but it offers no protection at all — anyone can decode it in seconds. And no service can "decrypt" a hash, because hashing deliberately destroys information; sites claiming to do so are looking values up in a table of previously seen inputs.
[SYMMETRIC AND ASYMMETRIC ENCRYPTION]
There are two families, and knowing which one a file uses tells you what you need in order to open it.
Symmetric — one shared key
The same key encrypts and decrypts. AES-256 and ChaCha20-Poly1305 work this way. It is fast and suits file encryption, but both parties need the same secret, so getting the key to the recipient safely is the hard part.
Asymmetric — a key pair
A public key encrypts, and only the matching private key decrypts. PGP and GnuPG work this way. It solves the key-distribution problem — you can publish your public key freely — at the cost of being slower and more complex to manage. In practice, tools use it to protect a symmetric key that does the actual work.
This is why decrypting a .gpg file requires the recipient's private key rather than the sender's public key — the most frequent stumbling block with PGP.
[COMMON ENCRYPTED FILE TYPES YOU WILL MEET]
.enc— generic; used by many unrelated programs, including this site.gpg.pgp.asc— GnuPG and PGP.7z.zip.rar— archives that may or may not be password-protected.kdbx— KeePass password database.hc.vc— VeraCrypt containers.axx.aes— AxCrypt and AES Crypt.crypt12.crypt14— WhatsApp message backups- Office files and PDFs — encryption lives inside the format itself, so the extension does not change
[FREQUENTLY ASKED QUESTIONS]
What is an encrypted file?
A file whose contents have been transformed by a cipher so that they cannot be read without the correct key. The file still occupies disk space and can be copied or emailed normally, but its contents are meaningless to anyone who does not hold the key.
What does an encrypted file look like?
Opened in a text editor it shows uniform, random-looking characters with no readable words anywhere — not at the start and not at the end. Some formats keep a short readable header describing the algorithm, but everything after it is noise.
How can I tell if a file is encrypted?
Look for high entropy and the complete absence of readable strings throughout the file. A corrupted file usually retains recognisable fragments, and a compressed file often still shows a format signature at the start. On Windows, a green filename in Explorer indicates EFS encryption.
Is an encrypted file safe to store in the cloud?
Yes — that is one of the main reasons to encrypt. A provider or an attacker who obtains the file gets only ciphertext. Two caveats: keep the key somewhere other than the same cloud account, and remember that the filename itself is usually visible.
Can an encrypted file contain a virus?
Yes. Encryption conceals contents; it does not inspect or sanitise them. A malicious file stays malicious once decrypted, and encryption is sometimes used specifically to slip past scanners that cannot read the contents. Only decrypt files from senders you trust.
Does encrypting a file make it bigger?
Marginally. The overhead is a fixed header, an initialisation vector and an authentication tag — typically a few hundred bytes regardless of file size. Compressing before encrypting usually makes the result smaller than the original.