Frequently Asked Questions


In command-line examples on this page, commands to be typed to the shell begin with a dollar sign “$”. Lines that do not begin with “$” show command output.

The text uses as a stand-in for your user name. If you run one of these commands, substitute your own name for that one.

The examples are Unix-oriented but it should be easy to adapt them to a Windows environment.

The project

What is Upspin?

Upspin attempts to provide a secure platform for naming, storing, and sharing information.

It is not a storage system first, it is a naming system. It provides protocols for secure storage and sharing that can be used by people, programs, providers, and products to build a single coherent way to talk about and manage data.

What are the goals of the project?

The cloud-oriented information world brought much to celebrate, but it is not always a seamless environment. It’s too often necessary to download a file only to upload it again to another service, or to make an item publicly accessible when the goal is just to make it accessible to one person.

Upspin addresses some of this clumsiness by providing a single, consistent experience that, if the project succeeds, will allow people to share data just by naming it, not by copying it around; to share it securely; to know who has access; and to unify the way information is accessed.

Why create something new rather than work on an existing system?

There are many systems out there that can provide some of what Upspin offers, but there is none that addresses its goals directly.

The combination of:

and other properties make Upspin unique.

Because of the dependence on simple federated protocols rather than a central service provider, it should be possible to unify other information service providers by connecting them through Upspin.

We prefer to think of Upspin as a complement to existing services rather than as a competitor to them.

Why use a central key server?

The global name space requires that there be only one meaning for any user name or path name. This approach, at least conceptually, requires a central key server. With multiple key servers, names could be ambiguous.

We are aware of the problems of a single point of failure that a central key server represents, but feel that with suitable engineering the risk can be mitigated.

The key server is a very simple service, and it could easily be replaced with another implementation. We hope one day to replace the existing server with one built on a public service such as Google’s Key Transparency project.

Can I use Upspin on my phone?

The story for Upspin on mobile devices is still evolving. It’s worth stressing that the idea of Upspin covers more than an app: it provides a way for all programs to see a consistent view of your data. Still, an Upspin app could be useful one day to simplify things like account management and sharing.

Can I access Upspin from a web browser?

To access arbitrary Upspin content from a web browser, the upspin-ui command serves a local web interface for working with Upspin trees.

Portions of Upspin may be made publicly accessible from the web, as is the case with the release tree, but there is no general web gateway for accessing Upspin content.

Why do writes always go to my own store server, even when writing to someone else’s directory?

When you create a file in another user’s directory, the storage for that file is placed in your storage server, not that of the directory’s owner. There are several reasons for this, but the most important is that it keeps accounting clean: you pay only for your storage; others pay for theirs.

There are other valuable results of this approach. It allows someone to build a shared directory without bearing all the cost of hosting everyone’s data. It also means that someone can’t consume your storage quota by filling your storage server with lots of data, either maliciously or accidentally.


Why use email addresses to identify users?

Email addresses are easily verified, externally managed names for people. They therefore provide a simple foundation upon which Upspin can build.

It’s important to realize that the name is only used as an actual email address during account creation. Once the user is registered, the user name looks like an email address, of course, but internally it is just a string. After signup it is never used by Upspin to send or receive mail.

Those worried about exposing a private email address can create a temporary one, register with it, and delete the email account afterwards. It would still serve as an Upspin user name. As a corollary, if the email account is hacked, lost, or transferred, that would have no effect on the security of the user’s data in Upspin.

The decision to use email addresses as user names would in principle be easy to change. It is just a name, after all. Upspin could replace the naming mechanism and one day may do so, although in practice we find email addresses work well.

Are there restrictions on Upspin user names?

Any valid email address is likely fine but since it will become as a user name within Upspin, the system applies some constraints that could invalidate some (very unusual) addresses. Also, within Upspin user names are case-sensitive, although in some email services the names are case-insensitive. The full story is a bit technical and irrelevant for most users, but if you are interested please see the description here.

How do I change the location of my directory and/or store servers?

If you change the location of your directory and store servers, you must update the values stored in the key server. One easy way to do this is to update the values in $HOME/config and run:

$ upspin user | upspin user -put


How do Upspin servers authenticate users?

Upspin clients identify themselves to Upspin servers with HTTP headers containing an authentication request signed with their private key. The details are described in the rpc package.

Are my files encrypted?

Although Upspin supports unencrypted (“plaintext”) files, we expect most users to employ end-to-end encryption to store their data. EE packing is the default for a storage server.

Files are also cryptographically signed, to detect tampering.

The process of encryption and decryption happens on the client, which means that neither the directory server nor the store server—nothing in the network—sees the unencrypted contents of the file.

How does encryption work?

For simplification, let’s discuss the most common case here, creating a file to be read by the owner alone.

When a file is created, it is encrypted using AES encryption with a unique “file key” that is generated by a random process at the time of creation of the file. AES is a symmetric encryption technology: it uses the same key to decrypt as to encrypt.

The file key is stored in the directory entry for the file, but that key is itself encrypted such that only the set of users with “read” access can decrypt it.

That second level of encryption is done using an elliptic curve algorithm, which uses distinct keys for encrypting and decrypting. The key for that encryption is the writer’s public key, the one saved in the key server at This approach means that only the person with the corresponding private key—the owner of the file—can recover the file key and use it to decrypt the original data.

To read the file, the owner takes the encrypted file key from the directory entry, decrypts it using the owner’s private key, and then decrypts the file’s contents using the file key.

The system is thus a two-level encryption method involving three keys: the AES file key and the writer’s public and private elliptic curve keys. The file key is unique for every file, while a given user’s public and private keys are the same in every file operation by that user throughout Upspin.

How does sharing work?

To be able to read an encrypted file, the reader must be able to acquire a cleartext version of the file key. Thus, every potential reader needs to have an encrypted file key stored in the directory entry.

If the list of readers is known when the file is created, the solution is simple: add to the directory entry an encrypted file key for each reader.

If a new reader, say a friend, is to be granted the right to read a file after it has been created, the first step is to use access control to give permission to the friend.

Then, the owner of the file decrypts the file key, just as in the case of reading the file, and encrypts another copy using the friend’s public key. The owner then saves both encryptions of the file key in the directory entry for the file.

In either case, when the friend wants to read the file, it’s the same procedure as for the owner: get the encrypted file key from the directory entry, decrypt that, and use it to decrypt the file.

What is the relationship between encryption and access control?

Access control defines who has access to a file or directory. There are several distinct rights that may be granted, including the right to read a file, but also to write one, to create one, to delete one, or to “list” one, that is, to see if it exists.

For a user to be able to read a file, the user must be granted access using the access control mechanisms described elsewhere. If the file is encrypted there must also be a copy of the file key encrypted with the user’s public key and stored in the directory entry, as described above,

Access control is a programmatic way to protect information, but is theoretically possible to subvert by malicious means such as through a compromised directory server. The file encryption technique, however, is much stronger and therefore provides the most important of protection of the data.

The relationship between access control and the storage of users’ keys in the directory entry can get out of sync. To bring them into alignment, use the upspin share command.

One day we hope to automate this reconciliation, but for now it must be done manually if read access control rights are changed after a file is written.

How can I trust the files I write are not modified?

Data stored in Upspin is cryptographically signed. The signature depends not only on the data, but also who wrote it and the original path name of the data, among other things. This means that the client can detect if a file has been tampered with, as it will see that the data (or writer or path name) does not match the signature with which it was created.

A packing (data storage method) called end-to-end integrity packing is available. This packing does not encrypt the data, but it still signs it, so even though the data can be stored in clear text, if it is tampered with, the tampering will be caught.

Are world-readable (“read:all”) files encrypted?

If you use the EE Packing (the default), world-readable files (Access and Group files, and any file shared with the permission read: all) are encrypted in StoreServer, but the decryption key is stored in clear text in the directory entry on the DirServer. This means that anyone with access to read the DirEntry may decrypt the objects in the StoreServer.

Can I share an individual file with other users?

Upspin’s access control mechanism works at the directory level and so there is no way to specify the access control rights for a specific file unless it is the only file in the directory. This seems inconvenient when you wish to share a specific file while keeping the others in that directory private, but there is a workaround.

File copies in Upspin are essentially free: if you upspin cp a file from one Upspin location to another then both files share the same underlying storage. To share a specific file with a specific user, create a directory for that user (, for example), put an Access file in that directory granting them read rights, and then use upspin cp to copy the file there.


Upspin users have a key pair for authentication and security. The details of their operation is covered in the Upspin Security document. The questions here cover the main points at a high level.

How are keys set up?

Every user has two keys. A public one is stored in the key server at and is visible to anyone. A secret key is coupled to the public key but is stored only on the local machine. It should never be shared with anyone or published. It should also be kept safely; if you lose it, you lose all access to Upspin, including the right to use your registered user name with the system.

Locally, these keys are stored, by default, in the directory


in files named public.upspinkey and secret.upspinkey.

See the document “not yet written” for a discussion of how keys provide security and safe sharing.

I lost my private key. How do I recover it?

When you signed up, you were encouraged to write down a “secret seed”, a string of letters that can be used to recreate your keys. It looks something like this:


Use that secret to recreate your public and private keys:

$ upspin keygen -secretseed zapal-zuhiv-visop-gagil.dadij-lnjul-takiv-fomin $HOME/.ssh/

This will write the private and public keys to the named directory. If you have a secrets field in your config that names a different directory, use that directory instead as the argument.

You can test that this has succeeded by running,

$ upspin user

This command will show you your configuration and also compare it with the record stored in the public key server at If there is any discrepancy, it will let you know.

How do I recreate my keys and config on another machine?

First generate the keys with the upspin keygen command and its -secretseed flag as described in the previous answer.

Then you must recreate your config file on the new machine. The easiest way is just to copy the existing one using scp or some equivalent. Examine it after copying and correct any settings that should be different on the new machine. See the Upspin configuration document for details.

I lost my secret seed. How do I recover it?

It is stored in your private key file, so if you still have that you can just look inside (the format is just one long line):

$ cat $HOME/.ssh/
25500039906333220349315666410231979076544554594099570935052437564736835632126 # javam-lumat-ganiv-jizan.vodos-huhuz-jogud-darin

If you have neither your secret seed nor your private key saved, you will be unable to access Upspin. There is no account recovery mechanism.

I lost my keys. How do I recover my account?

If you have your secret seed, see the previous sections.

Otherwise, you cannot recover your keys or your Upspin account.

Without your private key or secret seed to regenerate it, there is no mechanism to restore a lost account. Upspin attempts to be very secure, and it is our experience that account recovery mechanisms have historically been the weak link in account security. We believe the system is more secure by not providing one.

Do not lose your secret seed!

How do I delete my account on the key server?

If you decide to stop using Upspin, there is no need to remove anything from the key server.

The transaction log is cryptographically protected by a hash chain, so deletions are impossible anyway. This protects you from an adversary removing your public key and re-registering the account with their own key, locking you out and tricking your friends into leaking secrets.

How do I change my key?

Most people will never need to change their key; Upspin’s intent is that you share access to your files, not your keys. But sometimes a key change may be justified, so here are the details.

When you change your key, you migrate from one working key to another. The key change process maintains your old private key so you can authenticate you to the servers during the transition. When done, all your old keys will be saved so that you can still decrypt files from backups, but the old keys will no longer work for authentication.

Suppose you are on a client device with existing keys in the default directory $HOME/.ssh/ Here are the commands to switch to using a new key. Eventually these steps may be combined but at the moment it must be done in several steps, both to make it easier to recover if a step fails and so we can better understand people’s needs before designing a smoother process.

$ upspin keygen -rotate $HOME/.ssh/
$ upspin countersign
$ upspin rotate
$ upspin share -r -fix

As always, you must write down the secret seed printed by keygen and save it someplace safe!

The countersign and share commands may run for a few minutes as they walk your whole Upspin file tree. Also, if you have written files to other users’ directories, you must run share there as well.

After running those commands, you’re done! But if you want to understand what these commands mean, please read on.

The keygen command creates a new key pair in the two files,


It also saves old key pairs in


After running this one command, nothing has changed yet except the contents of these three files on your local system; you could revert to the old ones and be back where you started.

The countersign command walks through your Upspin file tree and adds signatures using the new key alongside those using the old. Recall that each file in Upspin is signed by the writer. There is room in each directory entry for a second signature, which in principle could be written by anyone else that wants to certify the file contents, somewhat analogous to the physical world requirement for some bank checks to be signed by one person and countersigned by another. Here the “other person” is you with your new key identity. After this command, files in your tree can be read and verified by anyone who knows your old or your new public key.

The rotate command pushes the new key to the public key server at, making it visible to others, who must now use your new key when sharing files with you. If there is a file you wrote (and signed) in someone else’s tree a long time ago and have not updated, readers will see an error because the signature will no longer verify; this can be fixed by running the share command.

The share command walks the specified file trees, re-wrapping the encryption keys to use the new keys instead. It’s a good idea to do this, but it’s not urgent because the secret2.upspinkey file holds the information necessary for the system to decrypt files that have not been updated.

However, if you are changing keys because you fear your old keys leaked, run share as soon as possible, to disassociate the files from your old key.


What does ‘“remote” not registered mean’?

If you write your own Upspin program and on startup it fails with an error like,

bind.KeyServer: service with transport "remote" not registered

it means your program is missing the code that connects it to the KeyServer implementation specified in the Upspin config file. The layer that makes this connection is called a transport, and remote is the transport that connects to a network service.

The simplest fix is to add the import declaration,

import _ ""

to the Go source file that defines the main function. This import collects all the transport implementations in the core Upspin libraries and adds them to your program.

The underscore in the import declaration is necessary. It tells the Go compiler that the import statement is being done for side effects only, in this case the linking into the binary of the full suite of transports.

Server administration

This section shows how to perform some common tasks around administrating an Upspin server installation. The examples assume you have signed up as as described in Signing up a new user and have set up upspinserver as a combined dirserver/storeserver for the domain Substitute your own user and domain names in the examples that follow.

How do I add a family member to my Upspin installation?

When you followed the server setup instructions, upspin setupserver created an initial version of the access control files for your Upspin installation that allows access for and the server user The key piece is a group file, owned by the server user, called Writers. This file specifies the complete list of Upspin users that, once authenticated, are allowed to write blocks to the server.

The easiest way to modify the Writers file is to use the upspin setupwriters command. The arguments list the users (or wildcards) to be granted access. The server user is always included automatically.

$ upspin setupwriters
# ... or with wildcards
$ upspin setupwriters '*'

Every time you call upspin setupwriters the Writers file is completely replaced; you must always include the full set of users to have write permission.

Another way to maintain the file is to edit it locally on your machine. To do this, you need to run the upspin command using the config file defined for the server user:

$ upspin -config=$HOME/upspin/deploy/ cp /tmp/Writers

Then edit it locally and copy it back once done:

$ upspin -config=$HOME/upspin/deploy/ cp /tmp/Writers

How do I delete unused blocks from my storage server?

The upspin audit command has a number of subcommands that allow an administrator to determine how much storage a given user is consuming, to see how much storage is used overall by the storage server, and to create a list of active blocks in the storage servers. After collecting such data, it can perform other tasks such as removing blocks from the storage server that are not referenced by the directory server.


$ upspin audit help

for more information.

The upspin audit command is simpleminded in its accounting and should be used with great care. In the presence of snapshots or multiple users sharing a storage server it is easy to make a mistake and delete active data. Use upspin audit with great care.