What is the AXX file format?
Files with the .axx extension are used by AxCrypt, a file encryption tool for Windows, macOS, Android, and iOS. An .axx file is an archive that stores encrypted and password-protected files.
The .axx format uses AES encryption - AES-128 in AxCrypt 1.x and AES-256 since AxCrypt 2.x (2016). To open an encrypted .axx archive, a password and an optional key file are needed. .axx files can therefore be used for secure distribution of attachments via email, and also as secure data archives.
Each .axx file begins with a fixed 16-byte GUID at offset 0 identifying it as an AxCrypt container. The original filename of the wrapped file is stored inside, also encrypted, and not visible without decryption. The payload may optionally be compressed before encryption. AxCrypt 2.x also supports key sharing with other authorized account holders. A related format is .axc.
Security & safety
RISK: LOWThe .axx format itself is a safe, legitimate encryption container (AES-128/256 with integrity checking) and contains no executable code. The genuine risks are practical: (1) a forgotten password means permanent data loss - AxCrypt has no master key/backdoor; (2) only download AxCrypt from the official axcrypt.net - search results for "axcrypt" and "open axx" surface fake "universal file viewers" and repackaged installers (PUP/adware) that cannot actually decrypt the file; (3) like any encrypted attachment, an .axx could wrap malware - only decrypt files from senders you trust.
Format details
in a nutshellPrograms that open AXX files
Windows1 app
AxCrypt
Freemium Install AxCrypt, sign in, double-click the .axx (or right-click > AxCrypt > Decrypt) and enter the encryption password. 
macOS1 app
Android1 app
Technical details
deep spec| Encryption algorithm (v1.x) | AES-128-CBC |
| Encryption algorithm (v2.x) | AES-256-CBC (since AxCrypt 2.x, 2016) |
| File identifier | Fixed 16-byte GUID at offset 0: C0 B9 07 2E 4F 93 F1 46 A0 15 79 2C A1 D9 E8 21 |
| Container structure | Typed header sections followed by the AES-encrypted payload |
| Original filename | Stored encrypted within the header; invisible to directory listings without decryption |
| Payload compression | Optional DEFLATE compression applied to plaintext before encryption |
| Integrity protection | HMAC over the ciphertext to detect tampering or corruption |
| Key derivation (v1.x) | Passphrase hashed with SHA-1 to produce the key-encryption key |
| Key derivation (v2.x) | PBKDF2-HMAC-SHA512 with high iteration count |
| Key file support | Optional binary key file provides a second authentication factor alongside the passphrase |
| Key sharing (v2.x) | Encrypted data key can be delegated to other AxCrypt account holders |
| Platform support | Windows, macOS, Android, iOS |
| MIME type | application/octet-stream |
| Developer | AxCrypt AB (formerly Axantum Software AB) |
| Released | 2001 (AxCrypt 1.x); AxCrypt 2.x with AES-256 since 2016 |
| Specification | www.axcrypt.net |
AXX conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about AXX files.
