harvey/sys/man/2/pushtls

.TH PUSHTLS 2
.SH NAME
pushtls, tlsClient, tlsServer, initThumbprints, freeThumbprints, okThumbprint, readcert \- attach TLS1 or SSL3 encryption to a communication channel
.SH SYNOPSIS
.B #include <u.h>
.br
.B #include <libc.h>
.PP
.B
int			pushtls(int fd, char *hashalg, char *encalg,
.br
.B
				int isclient, char *secret, char *dir)
.PP
.B #include <mp.h>
.br
.B #include <libsec.h>
.PP
.B
int			tlsClient(int fd, TLSconn *conn)
.PP
.B
int			tlsServer(int fd, TLSconn *conn)
.PP
.B
uchar		*readcert(char *filename, int *pcertlen)
.PP
.B
Thumbprint*	initThumbprints(char *ok, char *crl)
.PP
.B
void			freeThumbprints(Thumbprint *table)
.PP
.B
int			okThumbprint(uchar *hash, Thumbprint *table)
.SH DESCRIPTION
Transport Layer Security (TLS) comprises a record layer protocol,
doing message digesting and encrypting in the kernel,
and a handshake protocol,
doing initial authentication and secret creation at
user level and then starting a data channel in the record protocol.
TLS is nearly the same as SSL 3.0, and the software should interoperate
with implementations of either standard.
.PP
To use just the record layer, as described in
.IR tls (3),
call
.I pushtls
to open the record layer device, connect to the communications channel
.IR fd ,
and start up encryption and message authentication as specified
in
.IR hashalg ,
.IR encalg ,
and
.IR secret .
These parameters must have been arranged at the two ends of the
conversation by other means.
For example,
.I hashalg
could be
.BR sha1 ,
.I encalg
could be
.BR rc4_128 ,
and
.I secret
could be the base-64 encoding of two (client-to-server and server-to-client)
20-byte digest keys and two corresponding 16-byte encryption keys.
.I Pushtls
returns a file descriptor for the TLS data channel.  Anything written to this
descriptor will get encrypted and authenticated and then written to the
file descriptor,
.IR fd .
If
.I dir
is non-zero, the path name of the connection directory is copied into
.IR dir .
This path name is guaranteed to be less than 40 bytes long.
.PP
Alternatively, call
.I tlsClient
to speak the full handshake protocol,
negotiate the algorithms and secrets,
and return a new data file descriptor for the data channel.
.I Conn
points to a (caller-allocated) struct
.EX
   typedef struct TLSconn{
      char dir[40];     // OUT    connection directory
      uchar *cert;      // IN/OUT certificate
      uchar *sessionID; // IN/OUT sessionID
      int certlen, sessionIDlen;
      void (*trace)(char*fmt, ...);
   } TLSconn;
.EE
defined in
.IR tls.h .
On input, the caller can provide options such as
.IR cert ,
the local certificate, and
.IR sessionID ,
used by a client to resume a previously negotiated security association.
On output, the connection directory is set, as with
.B listen
(see
.IR dial (2)).
The input
.I cert
is freed and a freshly allocated copy of the remote's certificate
is returned in
.IR conn ,
to be checked by the caller
according to its needs.  One mechanism is supplied by
.I initThumbprints
and
.I freeThumbprints
which allocate and free, respectively, a table of hashes
from files of known trusted and revoked certificates.
.I okThumbprint
confirms that a particular hash is in the table, as computed by
.PP
.EX
   uchar hash[SHA1dlen];
   conn = (TLSconn*)mallocz(sizeof *conn, 1);
   fd = tlsClient(fd, conn);
   sha1(conn->cert, conn->certlen, hash, nil);
   if(!okThumbprint(hash,table))
      exits("suspect server");
   ...application begins...
.EE
.PP
Call
.I tlsServer
to perform the corresponding function on the server side:
.PP
.EX
   fd = accept(lcfd, ldir);
   conn = (TLSconn*)mallocz(sizeof *conn, 1);
   conn->cert = readcert("cert.pem", &conn->certlen);
   fd = tlsServer(fd, conn);
   ...application begins...
.EE
The private key corresponding to
.I cert.pem
should have been previously loaded into factotum, for example by
.EX
   auth/secretpem key.pem > /mnt/factotum/ctl
.EE
.PP
.I Conn
is not required for the ongoing conversation and may
be freed by the application whenever convenient.
.SH FILES
.TP 
.B /sys/lib/tls
thumbprints of trusted services, maintained manually
.SH SOURCE
.B /sys/src/libc/9sys/pushtls.c
.br
.B /sys/src/libsec/port
.SH "SEE ALSO"
.IR dial (2),
.IR tls (3),
.IR factotum (4),
.IR thumbprint (6)
.SH DIAGNOSTICS
return \-1 on failure.
.SH BUGS
.PP
Client certificates and client sessionIDs are not yet
implemented.
.PP
Note that in the TLS protocol
.I sessionID
itself is public;  it is used as a pointer to
secrets stored in factotum.