About this service

Secufile is a free file-transfer service run by the certified non-profit PAPS. No account is needed.

End-to-end encryption (E2EE)

For situations that demand the highest confidentiality, you can choose end-to-end encryption (E2EE). With E2EE, files and filenames are encrypted and decrypted entirely in your browser, and neither the keys nor the password are ever sent to the server. So no third party — including the operator — can decrypt the contents, whether in transit or while stored.

It suits businesses and individuals who put security first when exchanging files, such as confidential business documents, personal information, contracts, or evidence. The recipient decrypts the files in their own browser using the password.

E2EE can be enabled in the advanced settings. Because encryption and decryption run on your own device, it can be slower than the normal mode.

Why we make this public

At PAPS, we need to exchange evidence images and sensitive data securely with lawyers, law-enforcement agencies and others.

With ordinary email, even when the connection is encrypted, copies of a file can remain on mail services and at the destination. And if you send it to the wrong address, it is hard to fully undo afterwards.

These problems are not unique to support work. Anyone can face a situation where they want to send a file safely (personal information, contracts, photos, evidence) that they would rather others not see.

So we have opened the system PAPS actually needed in its support work as a free service anyone can use.

How files are protected

Each uploaded file is encrypted and stored with AES-256-GCM, using a random data-encryption key generated per file.

AES was adopted as the U.S. government standard cipher and is used worldwide to protect classified information, including in defense. AES-256 has been scrutinized for its security by cryptographers around the world over many years.

AES-256-GCM not only makes the contents unreadable, but can also verify that stored data has not been tampered with or corrupted. Secufile splits each file into fixed-size blocks and encrypts and authenticates each one.

What is Argon2id

Argon2id is a key derivation function designed to turn a password into a secure encryption key.

A password a person sets is usually shorter than a fully random key and may use dictionary words or predictable patterns. Using a password directly as an encryption key is therefore not safe.

Also, ordinary hash functions compute very fast, so an attacker can try a huge number of password candidates in a short time.

Argon2id deliberately uses not only a fixed amount of time per computation but also a large amount of memory. An attack that tries millions or billions of candidates at once with GPUs or dedicated hardware therefore needs a large amount of memory and computing resources.

For a user entering the correct password it is a one-time operation, but for an attacker trying countless candidates the cost adds up with each attempt. This greatly increases the time and money needed for a brute-force attack.

Argon2id combines the properties of Argon2i, which guards against information leakage while deriving a key, and Argon2d, which emphasizes resistance to brute-force attacks. It is recommended in the international technical document RFC 9106 and by OWASP.

By adopting Argon2id, Secufile increases resistance to password cracking compared with deriving an encryption key directly and simply from the password.

We do not store the password itself

What is stored on the server is the encrypted file and the encrypted data-encryption key. The password the user entered is stored nowhere on the server.

File names are encrypted too, so the contents cannot be guessed from a stored file name.

Therefore, even if only the data stored on the server were obtained, reading the contents without the password is extremely difficult.

Important: if you lose the password, the file cannot be recovered. Not even PAPS can check the password or recover the file. Using an easily guessed password (a short string or a common word) lowers security. Please use the auto-generated password, or set one that is long enough and hard to guess.

Communication is encrypted too

All communication between the browser and the Secufile server is encrypted with TLS (HTTPS).

This reduces the risk of a third party eavesdropping on the contents during upload or download.

Files are deleted automatically

A file is deleted automatically when either of the following is reached:

• the retention period set by the sender has passed
• the configured download limit has been reached

If the sender allows it, the recipient can also delete the file on the spot after downloading.

By not storing files longer than necessary, we reduce the risk of information lingering.

Information we record

To respond to rights infringement and to lawful requests for sender-information disclosure, we record and retain the uploader IP address.

If illegal information, or information that infringes the rights of others, is posted, we may disclose information to the relevant authorities or rights holders, in accordance with the law and the terms of use.

Secufile may not be used for the purpose of sharing illegal or harmful information.

Large files are supported

Files are uploaded in small parts.

If the connection drops partway, it resumes automatically from where it stopped once the connection recovers. Even on an unstable connection such as mobile, you do not have to resend from the beginning.

Downloads can also be resumed from where they were interrupted.

About the operator

Secufile is developed and operated by PAPS (a certified non-profit organization), which supports victims of sexual exploitation and digital sexual violence.

PAPS provides counseling support, help removing sexual images and videos, street outreach, safe spaces and accommodation for young women, and technology development to detect harm early.

The source code is open

The software that runs this service is published under the MIT license for anyone to read and verify: github.com/paps-jp/securefile

You can confirm how encryption and files are handled from the actual code, not just from our description. Being verifiable by third parties means you do not have to trust the operator unconditionally — transparency itself strengthens security.