Local Authenticated File Encryption

How to use Local Authenticated File Encryption

Encrypt or authenticate-decrypt one local file using a documented TJEF v1 AES-GCM password container, without uploading the bytes. Create a separate encrypted .tjenc artifact or recover its authenticated plaintext bytes. A fixed KDF cost, random salt/nonce and authenticated header keep the selected format explicit; it is not ZIP, OpenPGP or another encrypted-file standard.

1. Provide local input file, password: 16–256 unicode code points, repeat password for encryption only.
2. Choose the supported mode and run the tool. Review its assumptions and any reported errors.
3. Copy the result or download a separate output; reset to clear the current form.

Good to know

• Encrypt one file of 0–8,388,608 bytes, including empty files. Decrypt only a complete supported TJEF v1 container up to 8,388,668 bytes. Original files are not changed. Downloaded decrypted bytes use a generic .bin name; no original filename, MIME type or metadata is stored or automatically opened.
• Password input is literal well-formed Unicode, 16–256 code points and at most 1,024 UTF-8 bytes. Spaces and Unicode spelling are never trimmed or normalized; encryption requires an exact repeated password. Decryption ignores the repeat field. This length check is not a password-strength certification; use a strong unique password and retain it separately.
• TJEF v1 is a tool-specific documented format: 8-byte ASCII TJEFv1 plus CR LF magic, 4-byte big-endian fixed iteration count 600,000, 16-byte random salt, 12-byte random IV, 4-byte big-endian plaintext byte length, then AES-256-GCM ciphertext followed by its 16-byte tag. The complete 44-byte header is additional authenticated data. No other version, KDF cost, compression, algorithm or trailing bytes are accepted.
• The key is derived with PBKDF2-HMAC-SHA-256 at exactly 600,000 iterations. Each encryption draws a fresh 16-byte salt and 12-byte IV from native Web Crypto. These APIs and a secure browser context are required. Wrong passwords, tampering or truncation return no unauthenticated plaintext; a successful tag check authenticates this container under that password, not a sender identity.
• The fixed container header and ciphertext reveal the format and original byte length. The report returns sizes and the declared algorithms, never passwords, derived keys or plaintext. Input controls retain their text until cleared. JavaScript strings/crypto implementations cannot promise secure memory erasure, and an untrusted page/browser/device can still expose local input.
• The local module Worker prepares within 10 seconds before ready, then has a separate 2-second computation deadline including native PBKDF2/AES work. Slow devices can time out rather than weakening the fixed KDF. Output allocation stays bounded by the input size plus 60 bytes; no file is sent or automatically persisted.
• This custom format has no external interoperability, independent security-audit, FIPS-validation, archival-recovery or enterprise key-management claim. Password recovery is unavailable. Verify decryption of a separate test copy and keep original backups before relying on a new workflow.
• Structured text output is limited to 500,000 characters. Reduce the supplied source when that separate output budget is exceeded.
• Inputs are processed on this device and are not automatically saved or uploaded.