PUSHTLS(3) PUSHTLS(3)
NAME
pushtls, tlsClient, tlsServer, initThumbprints,
freeThumbprints, okThumbprint, readcert, readcertchain -
attach TLS1 or SSL3 encryption to a communication channel
SYNOPSIS
#include <u.h>
#include <libc.h>
int pushtls(int fd, char *hashalg, char *encalg,
int isclient, char *secret, char *dir)
#include <mp.h>
#include <libsec.h>
int tlsClient(int fd, TLSconn *conn)
int tlsServer(int fd, TLSconn *conn)
uchar *readcert(char *filename, int *pcertlen)
PEMchain *readcertchain(char *filename)
Thumbprint* initThumbprints(char *ok, char *crl)
void freeThumbprints(Thumbprint *table)
int okThumbprint(uchar *hash, Thumbprint *table)
DESCRIPTION
Transport Layer Security (TLS) comprises a record layer pro-
tocol, 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 chan-
nel in the record protocol. TLS is nearly the same as SSL
3.0, and the software should interoperate with implementa-
tions of either standard.
To use just the record layer, as described in Plan 9's
tls(3), call pushtls to open the record layer device, con-
nect to the communications channel fd, and start up encryp-
tion and message authentication as specified in hashalg,
encalg, and secret. These parameters must have been arranged
at the two ends of the conversation by other means. For
example, hashalg could be sha1, encalg could be rc4_128, and
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. Pushtls returns a
file descriptor for the TLS data channel. Anything written
to this descriptor will get encrypted and authenticated and
PUSHTLS(3) PUSHTLS(3)
then written to the file descriptor, fd. If dir is non-zero,
the path name of the connection directory is copied into
dir. This path name is guaranteed to be less than 40 bytes
long.
Alternatively, call tlsClient to speak the full handshake
protocol, negotiate the algorithms and secrets, and return a
new data file descriptor for the data channel. Conn points
to a (caller-allocated) struct
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, ...);
PEMChain *chain;
} TLSconn;
defined in tls.h. On input, the caller can provide options
such as cert, the local certificate, and sessionID, used by
a client to resume a previously negotiated security associa-
tion. On output, the connection directory is set, as with
listen (see dial(3)). The input cert is freed and a freshly
allocated copy of the remote's certificate is returned in
conn, to be checked by the caller according to its needs.
One mechanism is supplied by initThumbprints and
freeThumbprints which allocate and free, respectively, a
table of hashes from files of known trusted and revoked cer-
tificates. okThumbprint confirms that a particular hash is
in the table, as computed by
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...
Call tlsServer to perform the corresponding function on the
server side:
fd = accept(lcfd, ldir);
conn = (TLSconn*)mallocz(sizeof *conn, 1);
conn->cert = readcert("cert.pem", &conn->certlen);
fd = tlsServer(fd, conn);
...application begins...
The private key corresponding to cert.pem should have been
previously loaded into factotum. (See rsa(3) for more about
key generation.) By setting
conn->chain = readcertchain("intermediate-certs.pem");
the server can present extra certificate evidence to estab-
lish the chain of trust to a root authority known to the
PUSHTLS(3) PUSHTLS(3)
client.
Conn is not required for the ongoing conversation and may be
freed by the application whenever convenient.
FILES
/sys/lib/tls
thumbprints of trusted services
/sys/lib/ssl
PEM certificate files
SOURCE
/src/libsec/port
SEE ALSO
dial(3), thumbprint(7); Plan 9's factotum(4) and tls(3)
DIAGNOSTICS
return -1 on failure.
BUGS
Pushtls is not implemented.
Client certificates and client sessionIDs are not yet imple-
mented.
Note that in the TLS protocol sessionID itself is public;
it is used as a pointer to secrets stored in factotum.