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 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.

To use just the record layer, as described in Plan 9's tls(3), call pushtls to open the record layer device, connect to the communications 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 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 association. On output, the connection directory is set, as with listen (see 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 certificates. 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 for more about key generation.) By setting

   conn->chain = readcertchain("intermediate-certs.pem");

the server can present extra certificate evidence to establish 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.

FILES

/sys/lib/tls: thumbprints of trusted services
/sys/lib/ssl: PEM certificate files

SOURCE

/src/libsec/port

DIAGNOSTICS

return -1 on failure.

BUGS

Pushtls is not implemented.

Client certificates and client sessionIDs are not yet implemented.

Note that in the TLS protocol sessionID itself is public; it is used as a pointer to secrets stored in factotum.