pushtls(3) - Plan 9 from User Space

| 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 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 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 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 rsa(3) 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
| `/usr/lib/plan9/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 implemented.
Note that in the TLS protocol sessionID itself is public; it is used as a pointer to secrets stored in factotum.