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    This module has moved and is now available at @hapi/iron. Please update your dependencies as this version is no longer maintained an may contain bugs and security issues.

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    5.0.6 • Public • Published


    iron is a cryptographic utility for sealing a JSON object using symmetric key encryption with message integrity verification. Or in other words, it lets you encrypt an object, send it around (in cookies, authentication credentials, etc.), then receive it back and decrypt it. The algorithm ensures that the message was not tampered with, and also provides a simple mechanism for password rotation.

    Current version: 5.x

    Note: the wire protocol has not changed since 1.x (the version increments reflected a change in the internal error format used by the module and by the node API as well as other node API changes).

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    iron provides methods for encrypting an object, generating a message authentication code (MAC), and serializing both into a cookie / URI / HTTP header friendly format. Sealed objects are useful in cases where state has to reside on other applications not under your control, without exposing the details of this state to those application.

    For example, sealed objects allow you to encrypt the permissions granted to the authenticated user, store those permissions using a cookie, without worrying about someone modifying (or even knowing) what those permissions are. Any modification to the encrypted data will invalidate its integrity.

    The seal process follows these general steps:

    • generate encryption salt saltE
    • derive an encryption key keyE using saltE and a password
    • generate an integrity salt saltI
    • derive an integrity (HMAC) key keyI using saltI and the password
    • generate a random initialization vector iv
    • encrypt the serialized object string using keyE and iv
    • mac the encrypted object along with saltE and iv
    • concatenate saltE, saltI, iv, and the encrypted object into a URI-friendly string


    To seal an object:

    const obj = {
        a: 1,
        b: 2,
        c: [3, 4, 5],
        d: {
            e: 'f'
    const password = 'some_not_random_password_that_is_at_least_32_characters';
    try {
        const sealed = await Iron.seal(obj, password, Iron.defaults);
    } catch (err) {

    The result sealed object is a string which can be sent via cookies, URI query parameter, or an HTTP header attribute. To unseal the string:

    try {
        const unsealed = await Iron.unseal(sealed, password, Iron.defaults);
    } catch (err) {


    See the detailed API Reference.

    Security Considerations

    The greatest sources of security risks are usually found not in iron but in the policies and procedures surrounding its use. Implementers are strongly encouraged to assess how this module addresses their security requirements. This section includes an incomplete list of security considerations that must be reviewed and understood before using iron.

    Plaintext Storage of Credentials

    The iron password is only used to derive keys and is never sent or shared. However, in order to generate (and regenerate) the keys used to encrypt the object and compute the request MAC, the server must have access to the password in plaintext form. This is in contrast, for example, to modern operating systems, which store only a one-way hash of user credentials.

    If an attacker were to gain access to the password - or worse, to the server's database of all such password - he or she would be able to encrypt and decrypt any sealed object. Accordingly, it is critical that servers protect these passwords from unauthorized access.

    Frequently Asked Questions

    Where is the protocol specification?

    If you are looking for some prose explaining how all this works, there isn't any. iron is being developed as an open source project instead of a standard. In other words, the code is the specification. Not sure about something? Open an issue!

    Is it done?


    How come the defaults must be manually passed and not automatically applied?

    Because you should know what you are doing and explicitly set it. The options matter a lot to the security properties of the implementation. While reasonable defaults are provided, you still need to explicitly state you want to use them.


    Special thanks to Adam Barth for his infinite patience, and always insightful feedback and advice.

    The iron logo was based on original artwork created by Chris Carrasco.


    npm i iron

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