PUSHTLS(2) PUSHTLS(2)
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 tls(3), call
pushtls to open the record layer device, connect to the com-
munications channel fd, and start up encryption 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 then written to the file
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PUSHTLS(2) PUSHTLS(2)
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.
Certificates
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 session ID */
int certlen, sessionIDlen;
void (*trace)(char*fmt, ...);
PEMChain *chain;
char *sessionType; /* opt IN session type */
uchar *sessionKey; /* opt IN/OUT session key */
int sessionKeylen; /* opt IN session key length */
char *sessionConst; /* opt IN session constant */
} 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(2)). 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 way to check the remote certificate is to use
initThumbprints and freeThumbprints which allocate and free,
respectively, a table of hashes from files of known trusted
and revoked certificates. okThumbprint confirms that a par-
ticular hash is in the table.
TlsClient will optionally compute a session key for use by
higher-level protocols. To compute a session key, the
caller must set sessionType to a known session type;
sessionKeylen to the desired key length; sessionKey to a
buffer of length sessionKeylen; and sessionConst to the
desired salting constant. The only supported session type
is ttls, as used by 802.1x.
TlsServer executes the server side of the handshake. The
caller must initialize conn->cert, usually by calling
readcert to read and decode the PEM-encoded certificate from
filename, return a pointer to malloced storage containing
the certificate, and store its length through pcertlen. The
private key corresponding to cert.pem should have been pre-
viously loaded into factotum. (See rsa(8) for more about
key generation.)
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Readcertchain will read a PEM-encoded chain of certificates
from filename and return a pointer to a linked list of
malloced PEMChain structures, defined in tls.h:
typedef struct PEMChain PEMChain;
struct PEMChain {
PEMChain*next;
uchar *pem;
int pemlen;
};
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
client.
Conn is not required for the ongoing conversation and may be
freed by the application whenever convenient.
EXAMPLES
Start the client half of TLS and check the remote certifi-
cate:
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");
Run the server side:
fd = accept(lcfd, ldir);
conn = (TLSconn*)mallocz(sizeof *conn, 1);
conn->cert = readcert("cert.pem", &conn->certlen);
fd = tlsServer(fd, conn);
FILES
/sys/lib/tls thumbprints of trusted services
/sys/lib/ssl PEM certificate files
SOURCE
/sys/src/libc/9sys/pushtls.c
/sys/src/libsec/port
SEE ALSO
dial(2), tls(3), factotum(4), thumbprint(6)
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DIAGNOSTICS
Return -1 on failure.
BUGS
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.
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