LIBSASLC(3) BSD Library Functions Manual LIBSASLC(3)NAME
libsaslc, saslc.d, saslc_alloc, saslc_end, saslc_init, saslc_sess_init,
saslc_sess_end, saslc_sess_getprop, saslc_sess_setprop, saslc_sess_cont,
saslc_sess_decode, saslc_sess_encode, saslc_sess_getmech,
saslc_sess_strerror, saslc_strerror — Simple Authentication and Security
Layer client library
LIBRARY
library “libsaslc”
SYNOPSIS
#include <saslc.h>
saslc_t *
saslc_alloc(void);
int
saslc_end(saslc_t *ctx);
int
saslc_init(saslc_t *ctx, const char *appname, const char *cfgpath);
saslc_sess_t *
saslc_sess_init(saslc_t *ctx, const char *mechs, const char *secopts);
void
saslc_sess_end(saslc_sess_t *sess);
const char *
saslc_sess_getprop(saslc_sess_t *sess, const char *key);
int
saslc_sess_setprop(saslc_sess_t *sess, const char *key,
const char *value);
int
saslc_sess_cont(saslc_sess_t *sess, const void *in, size_t inlen,
void* *out, size_t *outlen);
ssize_t
saslc_sess_decode(saslc_sess_t *sess, const void *in, size_t inlen,
void* *out, size_t *outlen);
ssize_t
saslc_sess_encode(saslc_sess_t *sess, const void *in, size_t inlen,
void* *out, size_t *outlen);
const char *
saslc_sess_getmech(saslc_sess_t *sess);
const char *
saslc_sess_strerror(saslc_sess_t *sess);
const char *
saslc_strerror(saslc_t *ctx);
DESCRIPTION
The libsaslc library offers a client interface for the Simple Authentica‐
tion and Security Layer (SASL). The library is heavily influenced by its
use with postfix(1).
FUNCTIONS
The following functions are available in the library.
saslc_alloc()
The saslc_alloc() function allocates and returns a new saslc
context. The context is uninitialized: see saslc_init().
Returns NULL on error.
saslc_end(ctx)
The saslc_end() function destroys and deallocate resources used
by the context ctx. The context shouldn't have any sessions
assigned to it. Returns 0 on success and -1 if the context has
active sessions and cannot be deallocated.
saslc_init(ctx, appname, cfgpath)
The saslc_init() function initializes the saslc context ctx.
Based on the application name appname, it also parses the con‐
figuration files as indicated by cfgpath, sets up the context
and mechanism dictionaries, and creates mechanism list for the
context. If cfgpath is NULL, it checks the environment variable
SASLC_CONFIG for a location and if that is not found it uses the
default path /etc/saslc.d. Returns 0 on success and -1 on fail‐
ure.
saslc_sess_init(ctx, mechs, secopts)
The saslc_sess_init() function creates new session assigned to
the ctx context. The function chooses the mechanism to use for
authentication from the mechs list taking into account the
requirements from the secopts list. Both lists may be space or
comma delimited. The first matching mechanism from the mechs
list is used. See CONFIGURATION below for the supported mecha‐
nisms. The valid security options are
"noanonymous" reject anonymous mechanisms
"noplaintext" reject plaintext mechanisms
"nodictionary" reject mechanisms prone to dictionary
attack
"noactive" reject mechanisms prone to active non-
dictionary attacks
"mutual" require mutual authentication mechanisms
Unknown security options are ignored. Returns a session handle
or NULL on error or no match.
saslc_sess_end(sess)
The saslc_sess_end() function ends the sasl session sess. It
destroys and deallocates all internal resources. This does not
fail.
saslc_sess_getprop(sess, key)
The saslc_sess_getprop() function gets the property indicated by
the key from the saslc dictionaries. Dictionaries are searched
in following order: session sess dictionary, context dictionary
(global configuration), and mechanism dictionary. Returns the
property value or NULL if the property is not found.
saslc_sess_setprop(sess, key, value)
The saslc_sess_setprop() function sets the property indexed by
key to the value value in the session sess dictionary. If the
property already exists in the session dictionary, then the pre‐
vious value is replaced by the new value. If value is NULL,
then any previous value in the session dictionary is removed.
Returns 0 on success or -1 on failure.
saslc_sess_cont(sess, in, inlen, out, outlen)
The saslc_sess_cont() function performs one step of the sasl
authentication. It reads inlen bytes of input data (from the
server) from the in buffer and stores outlen bytes of output
data in out (for the server). The user is responsible for free‐
ing memory allocated for out. It returns 0 if the authentica‐
tion process is completed, 1 if another step is required, and -1
on error. Note that the completion of authentication process
does not mean the client is authenticated; that is determined by
the server.
saslc_sess_decode(sess, in, inlen, out, outlen)
The saslc_sess_encode() and saslc_sess_decode() functions are
used to provide the integrity ("auth-int") and confidentiality
("auth-int") layers for mechanisms that provide them. They
encode and, respectively, decode inlen bytes of data from the in
buffer using the method negotiated during authentication. On
error they return -1. Otherwise, they return the number of
bytes consumed from in and output outlen bytes of data in the
out buffer. The user is responsible for freeing memory allo‐
cated for out. If outlen is 0, more data is needed before any‐
thing can be output. Unused input data is stored internally for
use in subsequent calls.
When decoding, the internal buffers can only be flushed by pro‐
viding the missing packet data and it is an error to call
ssalc_sess_decode() with inlen = 0. The first call of
saslc_sess_decode() in a session must begin at the start of a
packet. Subsequent calls need not be aligned on packet bound‐
aries.
saslc_sess_encode(sess, in, inlen, out, outlen)
As described above, saslc_sess_encode() encodes inlen bytes of
data from the in buffer. Note that unlike when decoding, the
internal buffer may be flushed through the encoder by calling
saslc_sess_encode() with inlen = 0. In this case,
saslc_sess_encode() returns the number of bytes that were
flushed from the internal buffer.
saslc_sess_getmech(sess)
The saslc_sess_getmech() function returns the name of the mecha‐
nism used in the session sess. The function does not fail.
saslc_sess_strerror(sess)
The saslc_sess_strerror() returns the error message associated
with the session sess.
saslc_strerror(ctx)
The saslc_strerror() function operates as saslc_sess_strerror(),
but instead returns the error message string for the last error
in the context ctx. Neither function will ever return NULL.
CONFIGURATION
The library uses three types of dictionaries: context (or global), ses‐
sion, and mechanism, and they are searched in that order by
saslc_getprop() and the first matching entry is taken. The context and
mechanism dictionaries are loaded from configuration files, while the
session dictionary is loaded by the caller via saslc_setprop().
The configuration file <cfgpath>/<appname>/saslc.conf is used for the
configuration context. The <cfgpath>/<appname>/mech/<mechanism>.conf
file is used for the mechanism configuration. The <cfgpath> is
/etc/saslc.d by default, but this may be overridden by the environment
variable SASLC_CONFIG, which in turn may be overridden by saslc_init().
The <appname> is saslc by default, but may also be overridden by
saslc_init(). Finally, the <mechanism> is the mechanism in use by the
session as returned by saslc_sess_getmech(). Note that this name is case
sensitive. The currently supported mechanisms are
ANONYMOUS See RFC 2245 and RFC 4505.
CRAM-MD5 See RFC 2195.
DIGEST-MD5 See RFC 2831.
EXTERNAL See RFC 2222 section 7.4 and RFC 4422 appendix A.
GSSAPI See RFC 2222 section 7.2 and RFC 4752. This requires
GSS, Heimdal, or MIT Kerberos.
LOGIN Non-standard, but common.
PLAIN See RFC 2595 and RFC 4616.
If any of the mechanism files are missing they are silently ignored,
unless debugging is enabled.
The configuration files consists of lines of the form:
# comment line
⟨key⟩ ⟨value⟩ [# comment]
The ⟨key⟩ is a string beginning with an alpha character (isalpha(3)) fol‐
lowed by any number of alpha numeric (isalnum(3)) or underscore ‘_’ char‐
acters; this is case sensitive. The ⟨value⟩ is a number or a quoted
string. More than one ⟨key⟩ and ⟨value⟩ pair may occur on a single line,
but they may not be broken across lines. A ‘#’ character (outside a
quoted string) indicates that the rest of the line is a comment.
NOTE: Currently, no escaping is supported in strings, so they may not
contain quotes. Numbers must be between 0 and LLONG_MAX, inclusive. Any
base supported by strtoll(3) is allowed.
PROPERTIES
Most of the control of the library behavior is done via setting various
properties in the context or mechanism dictionaries via the configuration
files or in the session dictionary with saslc_setprop(). The following
properties are currently used, as defined in saslc.h:
SASLC_PROP_AUTHCID ("AUTHCID")
The authentication name (or username) to authenticate with. Used
by all mechanisms except EXTERNAL.
SASLC_PROP_AUTHZID ("AUTHZID")
The authorization string to use. By default, this string is
empty. Used by the DIGEST-MD5, EXTERNAL, and PLAIN mechanisms.
SASLC_PROP_BASE64IO ("BASE64IO")
If true ("true", "yes", or nonzero), then input and output
strings are base64 encoded. Any other value is false and the
input and output strings are not base64 encoded. By default,
this is assumed true. Used by all mechanisms.
SASLC_PROP_CIPHERMASK ("CIPHERMASK")
The mask of ciphers to use with the DIGEST-MD5 mechanism when
using the "auth-conf" QOP. By default all supported ciphers are
used, but they may be limited by a comma delimited list of cipher
names. The recognized cipher names for DIGEST-MD5 are:
3des Triple-DES Cipher in CBC "two keys" mode
with 112 bit key
aes AES Cipher in CBC mode with 128 bit key
des DES Cipher in CBC mode with 56 bit key
rc4 RC4 Cipher with 128 bit key
rc4-40 RC4 Cipher with 40 bit key
rc4-56 RC4 Cipher with 56 bit key
The default value is "des,3des,rc4,rc4_40,rc4_56,aes". (Note
that "aes" is not part of the official standard.) Used by the
DIGEST-MD5 mechanism.
SASLC_PROP_DEBUG ("DEBUG")
If true, then enable debug messages. This is implemented as a
global variable so it will affect all sessions. If set via
saslc_sess_setprop(), it should be set before the first call to
saslc_sess_cont(). (Also see the environment variable
SASLC_ENV_DEBUG in the ENVIRONMENT section below.)
SASLC_PROP_HOSTNAME ("HOSTNAME")
The fully qualified domain name of the server host. Used by the
DIGEST-MD5 and GSSAPI mechanisms.
SASLC_PROP_MAXBUF ("MAXBUF")
The size of the decode buffer. This info is sent to the server
so that it doesn't send packets that won't fit in the decode buf‐
fer when decoded. Used by the DIGEST-MD5 and GSSAPI mechanisms.
SASLC_PROP_PASSWD ("PASSWD")
The password to authenticate with. Used by the CRAM-MD5, DIGEST-
MD5, LOGIN, and PLAIN mechanisms.
SASLC_PROP_QOPMASK ("QOPMASK")
The mask of QOP (quality of protection) to use with the DIGEST-
MD5 and GSSAPI mechanisms. By default all supported QOP values
are allowed, but they may be limited by a comma delimited list of
QOP values. The recognized QOP values are:
auth authentication only
auth-int authentication with integrity
auth-conf authentication with confidentiality
so the default value of the mask is "auth,auth-int,auth-conf".
Used by the DIGEST-MD5 and GSSAPI mechanisms.
SASLC_PROP_REALM ("REALM")
A comma delimited list of possible realms to use for authentica‐
tion. The format of each element in the list is
"[⟨hostname⟩:]⟨realm⟩". The user specified realm is the first
realm in the list with a matching hostname or, if none is found,
the first realm in the list with no hostname. If the server pro‐
vides a list of realms, the one matching the user specified realm
is selected. If no match is found or if the user didn't provide
a realm, the first realm provided by the server is selected. If
the server doesn't provide any realms, use the user specified
realm if there is one, or the hostname if not. This is useful
when the server provides multiple realms or no realm. Used by
the DIGEST-MD5 mechanism.
SASLC_PROP_SECURITY ("SECURITY")
A comma delimited list of extra security option flags that will
be "or"-ed together with those passed to saslc_sess_init().
Since these flags are used to choose the session mechanism, they
are only effective if they are in the context configuration file.
(See the CONFIGURATION section and the saslc_sess_init()
function.)
SASLC_PROP_SERVICE ("SERVICE")
The service being used, e.g., smtp, imap, etc. Used by the
DIGEST-MD5 and GSSAPI mechanisms.
SASLC_PROP_SERVNAME ("SERVNAME")
A comma delimited list of possible service names with elements of
the form "[⟨hostname⟩:]⟨serv-name⟩" and with the same rules as
for the SASLC_PROP_REALM list. This should only be used if the
client uses a DNS name for the service that is different from the
FQDN of the server. For example, the service name example.com
might resolve (via SRV or MX records) into a set of other DNS
names, one of which, mail3.example.com, is the FQDN of the
server. (See RFC 2831 section 2.1.2 "serv-name".) Used by the
DIGEST-MD5 mechanism.
The defines in saslc.h should be used in code, but their values need to
be used in the config files.
ENVIRONMENT
The following environment variables (defined in saslc.h) affect the
behavior of the library:
SASLC_ENV_CONFIG ("SASLC_CONFIG")
If the environment variable SASLC_CONFIG is set it overrides the
default configuration file location of /etc/saslc.d. This may be
overridden by saslc_init().
SASLC_ENV_DEBUG ("SASLC_DEBUG")
If set, turn on debugging messages. This turns on debugging as
early as possible and is a global setting.
GSSAPI AND KERBEROS
The following is a minimal (Heimdal) Kerberos 5 setup for use with an
smtp server that has been configured to support SASL with the GSSAPI
mechanism. It assumes that Kerberos and the smtp server will both run on
server.my.domain and that the client is on client.my.domain. It also
assumes that the smtp server runs as user postfix and group mail, and
that it is not chrooted.
On server.my.domain run the following script as root and then start the
Kerberos server kdc(8). You will be prompted for a master password for
Kerberos and a password for the postfix principal.
#/bin/sh
cat <<- EOF >> /etc/krb5.conf
[libdefaults]
default_realm = MY.DOMAIN
[realms]
MY.DOMAIN = {
kdc = server.my.domain
admin_servers = server.my.domain
}
[domain_realm]
.my.domain = MY.DOMAIN
EOF
mkdir /var/heimdal
chown root:wheel /var/heimdal
chmod 755 /var/heimdal
kstash
kadmin -l init --realm-max-ticket-life=unlimited \
--realm-max-renewable-life=unlimited \
MY.DOMAIN
kadmin -l add --max-ticket-life="1 day" \
--max-renewable-life="1 week" \
--expiration-time=never \
--pw-expiration-time=never \
--attributes="" \
postfix
kadmin -l add --random-key \
--max-ticket-life="1 day" \
--max-renewable-life="1 week" \
--expiration-time=never \
--pw-expiration-time=never \
--attributes="" \
smtp/server.my.domain
kadmin -l ext -k /etc/krb5.keytab smtp/server.my.domain
chown root:mail /etc/krb5.keytab
chmod 640 /etc/krb5.keytab
Note that the keytab /etc/krb5.keytab must be readable by the smtp server
or authentication will fail. The location of this keytab file may be
changed with the environment variable KRB5_KTNAME. If postfix is the
smtp server, note the import_environment parameter (see postconf(5)).
On client.my.domain copy the keytab file from
server.my.domain:/etc/krb5.keytab to /etc/krb5.keytab. Setup the
/etc/saslc.d configuration directory (see CONFIGURATION above). Add the
line
AUTHCID "postfix"
to the file /etc/saslc.d/postfix/mech/GSSAPI.conf so that the postfix
principle will be used for authentication. Enable SASL in the smtp
client. Assuming the smtp client is postfix, you will need to add the
following to the /etc/postfix/main.cf file to do this:
smtp_sasl_auth_enable = yes
smtp_sasl_type = saslc
smtp_sasl_mechanism_filter = GSSAPI
relayhost = [server.my.domain]:submission
Here we have assumed the submission port is the port the server is lis‐
tening to. Finally, as root, run the command
su -m postfix -c kinit
to obtain a ticket for the postfix user with the postfix credential and
you should be good to go!
FILES
/etc/saslc.d
EXAMPLES
The following code fragments illustrate the possible use of the functions
described above.
int
decode_stream(saslc_sess_t *sess, int fdin, int fdout)
{
uint8_t buf[BUFSIZE];
uint8_t *in;
void *out;
size_t inlen, outlen;
ssize_t n, rval;
for (;;) {
if ((rval = read(fdin, buf, sizeof(buf))) == -1)
return -1;
if (rval == 0)
break;
in = buf;
inlen = rval;
while (inlen > 0) {
rval = saslc_sess_decode(sess, in, inlen, &out,
&outlen);
if (rval == -1)
return -1;
if (outlen > 0) {
n = write(fdout, out, outlen);
free(out);
if (n == -1)
return -1;
}
in += rval;
inlen -= rval;
}
}
return 0;
}
int
encode_stream(saslc_sess_t *sess, int fdin, int fdout)
{
uint8_t buf[BUFSIZE];
uint8_t *in;
void *out;
size_t inlen, outlen;
ssize_t n, rval;
for (;;) {
if ((rval = read(fdin, buf, sizeof(buf))) == -1)
return -1;
if (rval == 0)
break;
in = buf;
inlen = rval;
while (inlen > 0) {
rval = saslc_sess_encode(sess, in, inlen, &out,
&outlen);
if (rval == -1)
return -1;
if (outlen > 0) {
n = write(fdout, out, outlen);
free(out);
if (n == -1)
return -1;
}
in += rval;
inlen -= rval;
}
}
/* flush internal encoder buffer */
if (saslc_sess_encode(sess, NULL, 0, &out, &outlen) == -1)
return -1;
if (outlen > 0)
if (write(fdout, out, outlen) == -1)
return -1;
return 0;
}
COMPATIBILITY
There exist other SASL client library implementations including Cyrus
SASL (http://asg.web.cmu.edu/sasl/sasl-library.html) and GNU SASL
(http://www.gnu.org/software/gsasl/).
STANDARDS
RFC 2195, RFC 2222, RFC 2245, RFC 2595, RFC 2831, RFC 4422, RFC 4505, RFC
4616, RFC 4752.
HISTORY
The libsaslc library appeared in NetBSD 6.0.
CAVEATS
The API was heavily influenced by its use with postfix(1).
Currently the ANONYMOUS, LOGIN, PLAIN, CRAM-MD5, DIGEST-MD5, and GSSAPI
mechanisms have been tested and shown to work for authentication with a
postfix(1) SMTP server using the cyrus-sasl library. LOGIN, PLAIN, CRAM-
MD5, and DIGEST-MD5 have also been tested and shown to work with a
postfix(1) SMTP server using a dovecot backend for authentication. The
DIGEST-MD5 and GSSAPI specs also provide for integrity and confidential‐
ity layers via the saslc_sess_encode() and saslc_sess_decode() routines,
but these have not yet been tested against any servers.
BSD September 23, 2011 BSD
