NAME

factotum - authentication agent

SYNOPSIS

factotum [ -DdkSun ] [ -a authaddr ] [ -s srvname ]

factotum -g attribute=value ... attribute? ...

DESCRIPTION

Factotum is a user-level file system that acts as the authentication agent for a user. It does so by managing a set of keys. A key is a collection of information used to authenticate a particular action. Stored as a list of attribute=value pairs, a key typically contains a user, an authentication domain, a protocol, and some secret data.

Factotum presents the following files:

rpc: each open represents a new private channel to factotum
proto: when read lists the protocols available
confirm: for confiming the use of key
needkey: allows external programs to control the addition of new keys
log: a log of actions
ctl: for maintaining keys; when read, it returns a list of keys. For secret attributes, only the attribute name follow by a is returned.

In any authentication, the caller typically acts as a client and the callee as a server. The server determines the authentication domain, sometimes after a negotiation with the client. Authentication always requires the client to prove its identity to the server. Under some protocols, the authentication is mutual. Proof is accomplished using secret information kept by factotum in conjunction with a cryptographic protocol.

Factotum can act in the role of client for any process possessing the same user id as it. For select protocols such as p9sk1 it can also act as a client for other processes provided its user id may speak for the other process' user id (see Plan 9's authsrv(6)). Factotum can act in the role of server for any process.

Factotum's structure is independent of any particular authentication protocol. Factotum supports the following protocols:

p9any: a metaprotocol used to negotiate which actual protocol to use.
p9sk1: a Plan 9 shared key protocol.
p9sk2: a variant of p9sk1.
p9cr: a Plan 9 protocol that can use either p9sk1 keys or SecureID tokens.
apop: the challenge/response protocol used by POP3 mail servers.
cram: the challenge/response protocol also used by POP3 mail servers.
chap: the challenge/response protocols used by PPP and PPTP.
dsa: DSA signatures, used by SSH
mschap: a proprietary Microsoft protocol also used by PPP and PPTP.
rsa: RSA encryption and signatures, used by SSH and TLS.
pass: passwords in the clear.
vnc: challenge/response.
wep: WEP passwords for wireless ethernet cards. The ``Protocols'' section below describes these protocols in more detail.

The options to factotum are:

-a: supplies the address of the authentication server to use. Without this option, it will attempt to find an authentication server by querying the connection server, the file <mtpt>/ndb, and finally the network database in /lib/ndb.
-m: specifies the mount point to use, by default /mnt.
-s: specifies the service name to use. Without this option, factotum does not create a service file in /srv.
-D: turns on 9P tracing, written to standard error.
-d: turns on debugging, written to standard error.
-g: causes the agent to prompt for the key, write it to the ctl file, and exit. The agent will prompt for values for any of the attributes ending with a question mark (?) and will append all the supplied attribute = value pairs. See the section on key templates below.
-n: don't look for a secstore.
-S: indicates that the agent is running on a cpu server. On starting, it will attempt to get a 9psk1 key from NVRAM using readnvram (see prompting for anything it needs. It will never subsequently prompt for a key that it doesn't have. This option is typically used by the kernel at boot time.
-k: causes the NVRAM to be written. It is only valid with the -S option. This option is typically used by the kernel at boot time.
-u: causes the agent to prompt for user id and writes it to /dev/hostowner. It is mutually exclusive with -k and -S. This option is typically used by the kernel at boot time.

Key Tuples

A key tuple is a space delimited list of attribute=value pairs. An attribute whose name begins with an exclamation point (!) does not appear when reading the ctl file. Here are some examples:

    proto=p9sk1 dom=avayalabs.com user=presotto !password=lucent
    proto=apop server=mit.edu user=rsc !password=nerdsRus
    proto=pass user=tb service=ssh !password=does.it.matter

The ``Protocols'' section below describes the attributes specific to each supported protocol.

All keys can have additional attibutes that act either as comments or as selectors to distinguish them in the library calls.

The factotum owner can use any key stored by factotum. Any key may have one or more owner attributes listing the users who can use the key as though they were the owner. For example, the TLS and SSH host keys on a server often have an attribute owner=* to allow any user (and in particular, to run the TLS or SSH server-side protocol.

Any key may have a role attribute for restricting how it can be used. If this attribute is missing, the key can be used in any role. Common values are:

client: for authenticating outbound calls
server: for authenticating inbound calls
speaksfor: for authenticating processes whose user id does not match factotum's.
encrypt: for encrypting data
decrypt: for decrypting data
sign: for cryptographically signing data
verify: for verifying cryptographic signatures

Whenever factotum runs as a server, it must have a p9sk1 key in order to communicate with the authentication server for validating passwords and challenge/responses of other users.

Key Templates

Key templates are used by routines that interface to factotum such as auth_proxy and auth_challenge (see to specify which key and protocol to use for an authentication. Like a key tuple, a key template is also a list of attribute=value pairs. It must specify at least the protocol and enough other attributes to uniquely identify a key, or set of keys, to use. The keys chosen are those that match all the attributes specified in the template. The possible attribute/value formats are:

attr=val: The attribute attr must exist in the key and its value must exactly match val
attr?: The attribute attr must exist in the key but its value doesn't matter.
attr: The attribute attr must exist in the key with a null value

Key templates are also used by factotum to request a key either via an RPC error or via the needkey interface. The possible attribute/value formats are:

attr=val: This pair must remain unchanged
attr?: This attribute needs a value
attr: The pair must remain unchanged

Control and Key Management

A number of messages can be written to the control file. The mesages are:

key attribute-value-list: add a new key. This will replace any old key whose public, i.e. non ! attributes, match.
delkey attribute-value-list: delete a key whose attributes match those given.
debug: toggle debugging on and off, i.e., the debugging also turned on by the -d option.

By default when factotum starts it looks for a account on $auth for the user and, if one exists, prompts for a secstore password in order to fetch the file factotum, which should contain control file commands. An example would be

  key dom=x.com proto=p9sk1 user=boyd !hex=26E522ADE2BBB2A229
  key proto=rsa service=ssh size=1024 ek=3B !dk=...

where the first line sets a password for challenge/response authentication, strong against dictionary attack by being a long random string, and the second line sets a public/private keypair for ssh authentication, generated by ssh_genkey (see

Confirming key use

The confirm file provides a connection from factotum to a confirmation server, normally the program auth/fgui. Whenever a key with the confirm attribute is used, factotum requires confirmation of its use. If no process has confirm opened, use of the key will be denied. However, if the file is opened a request can be read from it with the following format:

confirm tag=tagno <key template>

The reply, written back to confirm, consists of string:

tag=tagno answer=xxx

If xxx is the string yes then the use is confirmed and the authentication will proceed. Otherwise, it fails.

Confirm is exclusive open and can only be opened by a process with the same user id as factotum.

Prompting for keys

The needkey file provides a connection from factotum to a key server, normally the program auth/fgui. Whenever factotum needs a new key, it first checks to see if needkey is opened. If it isn't, it returns a error to its client. If the file is opened a request can be read from it with the following format:

needkey tag=tagno <key template>

It is up to the reader to then query the user for any missing fields, write the key tuple into the ctl file, and then reply by writing into the needkey file the string:

tag=tagno

Needkey is exclusive open and can only be opened by a process with the same user id as factotum.

The RPC Protocol

Authentication is performed by

1): opening rpc
2): setting up the protocol and key to be used (see the start RPC below),
3): shuttling messages back and forth between factotum and the other party (see the read and write RPC's) until done
4): if successful, reading back an AuthInfo structure (see

The RPC protocol is normally embodied by one of the routines in We describe it here should anyone want to extend the library.

An RPC consists of writing a request message to rpc followed by reading a reply message back. RPC's are strictly ordered; requests and replies of different RPC's cannot be interleaved. Messages consist of a verb, a single space, and data. The data format depends on the verb. The request verbs are:

start attribute-value-list: start a new authentication. Attribute-value-pair-list must include a proto attribute, a role attribute with value client or server, and enough other attibutes to uniquely identify a key to use. A start RPC is required before any others. The possible replies are:

ok: start succeeded.
error string: where string is the reason.

read: get data from factotum to send to the other party. The possible replies are:

ok: read succeeded, this is zero length message.
ok data: read succeeded, the data follows the space and is unformatted.
done: authentication has succeeded, no further RPC's are necessary
done haveai: authentication has succeeded, an AuthInfo structure (see can be retrieved with an authinfo RPC
phase string: its not your turn to read, get some data from the other party and return it with a write RPC.
error string: authentication failed, string is the reason.
protocol not started: a start RPC needs to precede reads and writes
needkey attribute-value-list: a key matching the argument is needed. This argument may be passed as an argument to factotum -g in order to prompt for a key. After that, the authentication may proceed, i.e., the read restarted.

write data: send data from the other party to factotum. The possible replies are:

ok: the write succeeded
needkey attribute-value-list: see above
toosmall n: the write is too short, get more data from the other party and retry the write. n specifies the maximun total number of bytes.
phase string: its not your turn to write, get some data from factotum first.
done: see above
done haveai: see above

readhex, writehex: like read and write, except that an ok response to readhex returns the data encoded as a long hexadecimal string, and the argument to writehex is expected to be a long hexadecimal string. These are useful for manually debugging of binary protocols.
authinfo: retrieve the AuthInfo structure. The possible replies are:

ok data: data is a marshaled form of the AuthInfo structure.
error string: where string is the reason for the error.

attr: retrieve the attributes used in the start RPC. The possible replies are:

ok attribute-value-list
error string: where string is the reason for the error.

Protocols

Factotum supports many authentication types, each with its own roles and required key attributes.

P9any, p9sk1, p9sk2, and p9cr are used to authenticate to Plan 9 systems; valid roles are client and server. All require proto=p9sk1 keys with user, dom (authentication domain), and !password attributes.

P9sk1 and p9sk2 are the Plan 9 shared-key authentication protocols. P9sk2 is a deprecated form of p9sk1 that neglects to authenticate the server.

P9any is a meta-protocol that negotiates a protocol (p9sk1 or p9sk2) and an authentication domain and then invokes the given protocol with a dom= attribute.

P9any, p9sk1, and p9sk2 are intended to be proxied via auth_proxy (see

P9cr is a textual challenge-response protocol; roles are client and server. It uses p9sk1 keys as described above. The protocol with factotum is textual: client writes a user name, server responds with a challenge, client writes a response, server responds with ok or bad. Typically this information is wrapped in other protocols before being sent over the network.

Vnc is the challenge-response protocol used by valid roles are client and server. The client protocol requires a proto=vnc key with attribute !password. Conventionally, client keys also have user and server attributes. The server protocol requires a p9sk1 key as described above. The protocol with factotum is the same as p9cr, except that the challenge and response are not textual.

Apop and cram are challenge-response protocols typically used to authenticate to mail servers. The client protocols require proto=apop or proto=cram keys with user and !password attributes. Conventionally, client keys also have server attributes. The server protocol requires a p9sk1 key as described above. The protocol with factotum is textual: server writes a challenge of the form random@domain, client responds with user name and then a hexadecimal response (two separate writes), and then the server responds with ok or bad.

Chap and mschap are challenge-response protocols used in PPP sessions; valid roles are client and server. The client protocols require proto=chap or proto=mschap keys with user and !password attributes. Conventionally, client keys also have server attributes. The server protocol requires a p9sk1 key as described above. The protocol with factotum is: server writes an 8-byte binary challenge, client responds with user name and then a Chapreply or MSchapreply structure (defined in <auth.h> ).

Pass is a client-only protocol that hands out passwords from proto=pass keys with user and !password attributes. The protocol is a single read that returns a string: a space-separated quoted user name and password that can be parsed with tokenize (see Conventionally, client keys have distinguishing attributes like service and server that can be specified in the start message to select a key.

Wep is a client-only pseudo-protocol that initializes the encryption key on a wireless ethernet device. It uses proto=wep keys with !key1, !key2, or !key3 attributes. The protocol with factotum is: the client writes a device name that must begin with In response, factotum opens the device's control file, sets the wireless secret using the key, and turns on encryption. If the key has an essid attribute, factotum uses it to set the wireless station ID.

Rsa is an implementation of the RSA protocol. Valid roles are decrypt, encrypt, sign, and verify. Rsa uses proto=rsa keys with ek and n attributes, large integers specifying the public half of the key. If a key is to be used for decryption or signing, then it must also have attributes !p, !q, !kp, !kq, !c2, and !dk specifying the private half of the key; see Conventionally, rsa keys also have service attributes specifying the context in which the key is used: ssh (SSH version 1), ssh-rsa (SSH version 2), or tls (SSL and TLS). If an SSH key has a comment attribute, that comment is presented to remote SSH servers during key negotiation. The protocol for encryption (decryption) is: write the message, then read back the encrypted (decrypted) form. The protocol for signing is: write a hash of the actual message, then read back the signature. The protocol for verifying a signature is: write the message hash, write the purported signature, then read back ok or bad telling whether the signature could be verified. The hash defaults to SHA1 but can be specified by a hash attribute on the key. Valid hash functions are md5 and sha1. The hash function must be known to factotum because the signature encodes the type of hash used. The encrypt and verify operations are included as a convenience; factotum is not using any private information to perform them.

Dsa is an implementation of the NIST digital signature algorithm. Valid roles are sign and verify. It uses proto=dsa keys with p, q, alpha, and key attributes. If the key is to be used for signing, it must also have a !secret attribute; see Conventionally, dsa keys also have service attributes specifying the context in which the key is used: ssh-dss (SSH version 2) is the only one. If an SSH key has a comment attribute, that comment is presented to SSH servers during key negotiation. The protocol for signing and verifying is the same as the RSA protocol. Unlike rsa, the dsa protocol ignores the hash attribute; it always uses SHA1.

Httpdigest is a client-only MD5-based challenge-response protocol used in HTTP; see RFC 2617. It uses proto=httpdigest keys with user, realm, and !password attributes. The protocol with factotum is textual: write the challenge, read the response. The challenge is a string with three space-separated fields nonce, method, and uri, parseable with tokenize. The response is a hexadecimal string of length 32.

SOURCE

/src/cmd/auth/factotum