What is the ID file format?
.id files are used by HCL Notes (formerly Lotus Notes, developed by IBM and now maintained by HCLSoftware), a client-server collaboration ecosystem for Windows, macOS, and Linux. .id files store HCL Notes user identification data and _Domino_ server credential data.
Identification data comprises:
- username,
- public and private keys,
- security certificate,
- license number for the Notes software,
- password.
.id files are created by platform administrators and are valid for a defined period of time, usually a year. They need to be renewed after expiring. Data in .id files is sensitive and should be secured properly, as it grants access to the server and to all encrypted mail and documents tied to that identity.
Since HCL Notes/Domino 8.5, administrators can store and recover .id files centrally using the Domino ID vault, reducing the risk of permanent credential loss. The file is a compact proprietary encrypted binary container, typically just a few kilobytes in size, and is used alongside other HCL Domino formats such as .NSF mail and application databases.
Security & safety
RISK: HIGHThe ID file contains the user's PRIVATE keys, so it is a high-value secret, not a document. Whoever holds the .id and its password can impersonate the user and decrypt all their encrypted Notes mail and data. Never e-mail or share an .id, store it only in secure/encrypted locations, use a strong ID password, and rely on the Domino ID vault for recovery. Conversely, if you lose the .id and its password and there is no vault copy, the encrypted data is unrecoverable - there is no backdoor. Treat a leaked ID file as a serious security incident (re-certify/replace the user's keys).
Format details
in a nutshell- Generic application identifier / index (.id) - Many programs and games drop tiny .id files holding a serial, GUID or index - unrelated to Lotus Notes and not openable as documents.
- Tax/registration ID export files - Some accounting and registration tools name small data exports .id; format is app-specific.
Programs that open ID files
Windows2 apps
HCL Notes
Paid The Notes client uses the ID to log in (File > Security > User Security to inspect certificates/keys). You authenticate with it, not 'open' it.
HCL Domino Administrator
Paid Admins manage user/certifier IDs, the ID vault and recovery from the Domino admin client. 
macOS1 app
HCL Notes (macOS)
Paid Same role on macOS: the Notes client uses the ID file to authenticate the user. 
Linux1 app
Technical details
deep spec| File type | Encrypted credential and identity file (private keys + certificates) |
| Encoding | Binary - opaque proprietary encrypted container |
| Encryption | Password-protected; holds the user's private RSA and AES keys; access requires the ID password |
| Typical file size | ~3-10 KB |
| Content stored | Owner name, Notes/Domino certificates, license number, public and private encryption/signing keys |
| File signature (magic bytes) | No publicly documented signature; identified by extension and context, not a published magic number |
| Certificate authority | Domino certifier - hierarchical PKI within the Notes/Domino organisation |
| Validity period | Issued for a fixed term (typically one year); must be renewed by a Domino administrator before expiry |
| ID vault support | Centralised storage and recovery via the Domino ID vault, introduced in Notes/Domino 8.5 (2009) |
| Integrity mechanism | Tied to the certificate/key chain issued by the Domino certifier; tampering renders the ID unusable |
| MIME type | application/octet-stream |
| Supported platforms | Windows, macOS, Linux - wherever the HCL Notes client runs |
| Developer history | Lotus Development (1989) → IBM (1995) → HCLSoftware (2019) |
| Related formats | .nsf (Notes database), .ntf (Notes template), .ndk (Notes ID backup) |
| Released | 1989 (Lotus Notes 1.0) |
| Latest version | Current with HCL Notes/Domino 14 (ID vault and modern crypto supported) |
| Specification | help.hcl-software.com |
ID conversions
Community Q&A
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