ssl-available?
ssl-load-fail-reason
1 TCP-like Client Procedures
ssl-connect
ssl-connect/ enable-break
ssl-make-client-context
ssl-client-context?
2 TCP-like Server Procedures
ssl-listen
ssl-close
ssl-listener?
ssl-accept
ssl-accept/ enable-break
ssl-make-server-context
ssl-server-context?
3 SSL-wrapper Interface
ports->ssl-ports
4 Context Procedures
ssl-load-certificate-chain!
ssl-load-private-key!
ssl-set-verify!
ssl-load-verify-root-certificates!
ssl-load-suggested-certificate-authorities!
5 Implementation Notes
Version: 4.1.2

OpenSSL

 (require openssl)

The openssl library provides glue for the OpenSSL library with the Scheme port system. It provides functions nearly identically to the standard TCP subsystem in PLT Scheme, plus a generic ports->ssl-ports interface.

To use this library, you will need OpenSSL installed on your machine, but

ssl-available? : boolean?

A boolean value which says whether the system openssl library was successfully loaded. Calling ssl-connect, etc. when this value is #f (library not loaded) will raise an exception.

ssl-load-fail-reason : (or/c false/c string?)

Either #f (when ssl-available? is #t) or an error string (when ssl-available? is #f).

1 TCP-like Client Procedures

(ssl-connect hostname    
  port-no    
  [client-protocol])  
input-port? output-port?
  hostname : string?
  port-no : (integer-in 1 65535)
  client-protocol : (or/c ssl-client-context? symbol?)
   = 'sslv2-or-v3

Connect to the host given by hostname, on the port given by port-no. This connection will be encrypted using SSL. The return values are as for tcp-connect: an input port and an output port.

The optional client-protocol argument determines which encryption protocol is used, whether the server’s certificate is checked, etc. The argument can be either a client context created by ssl-make-client-context, or one of the following symbols: 'sslv2-or-v3 (the default), 'sslv2, 'sslv3, or 'tls; see ssl-make-client-context for further details (including the meanings of the protocol symbols).

Closing the resulting output port does not send a shutdown message to the server. See also ports->ssl-ports.

Beware that the SSL protocol allows reading or writing in only one direction at a time. If you request data from the input port, then data cannot be written to the output port (i.e., attempting to write will block) until the other end of the connection responds to the read. Even merely checking for input data – using byte-ready?, for example – commits the connection to reading, and the other end must respond with a (possibly zero-length) answer. Protocols that work with SSL, such as IMAP, have a well-defined communication pattern, where theres no question of whether the other end is supposed to be sending or reading data.

(ssl-connect/enable-break hostname 
  port-no 
  [client-protocol]) 
  
input-port? output-port?
  hostname : string?
  port-no : (integer-in 1 65535)
  client-protocol : (or/c ssl-client-context? symbol?)
   = 'sslv2-or-v3

)]{

Like ssl-connect, but breaking is enabled while trying to connect.}

(ssl-make-client-context [protocol])  ssl-client-context?
  protocol : symbol? = 'sslv2-or-v3

Creates a context to be supplied to ssl-connect. The context identifies a communication protocol (as selected by protocol), and also holds certificate information (i.e., the client’s identity, its trusted certificate authorities, etc.). See the section Context Procedures below for more information on certificates.

The protocol must be one of the following:

By default, the context returned by ssl-make-client-context does not request verification of a server’s certificate. Use ssl-set-verify! to enable such verification.

(ssl-client-context? v)  boolean?
  v : any/c

Returns #t if v is a value produced by ssl-make-client-context, #f otherwise.

2 TCP-like Server Procedures

(ssl-listen port-no    
  queue-k    
  [reuse?    
  hostname-or-#f    
  server-protocol])  ssl-listener?
  port-no : (integer-in 1 65535)
  queue-k : exact-nonnegative-integer?
  reuse? : any/c = #f
  hostname-or-#f : (or/c string? false/c) = #f
  server-protocol : (or/c ssl-server-context? symbol?)
   = 'sslv2-or-v3

Like tcp-listen, but the result is an SSL listener (which is a synchronizable value; see sync). The extra optional server-protocol is as for ssl-connect, except that a context must be a server context instead of a client context.

Call ssl-load-certificate-chain! and ssl-load-private-key! to avoid a no shared cipher error on accepting connections. The file "test.pem" in the "openssl" collection is a suitable argument for both calls when testing. Since "test.pem" is public, however, such a test configuration obviously provides no security.

(ssl-close listener)  void?
  listener : ssl-listener?
(ssl-listener? v)  boolean?
  v : any/c

Analogous to tcp-close and tcp-listener?.

(ssl-accept listener)  
input-port? output-port?
  listener : ssl-listener?
(ssl-accept/enable-break listener)  
input-port? output-port?
  listener : ssl-listener?

Analogous to tcp-accept.

Closing the resulting output port does not send a shutdown message to the client. See also ports->ssl-ports.

See also ssl-connect about the limitations of reading and writing to an SSL connection (i.e., one direction at a time).

The ssl-accept/enable-break procedure is analogous to tcp-accept/enable-break.

(ssl-make-server-context protocol)  ssl-server-context?
  protocol : symbol?

Like ssl-make-client-context, but creates a server context.

(ssl-server-context? v)  boolean?
  v : any/c

Returns #t if v is a value produced by ssl-make-server-context, #f otherwise.

3 SSL-wrapper Interface

(ports->ssl-ports input-port 
  output-port 
  [#:mode mode 
  #:context context 
  #:encrypt protocol 
  #:close-original? close-original? 
  #:shutdown-on-close? shutdown-on-close? 
  #:error/ssl error]) 
  
input-port? output-port?
  input-port : input-port?
  output-port : output-port?
  mode : symbol? = 'accept
  context : (or/c ssl-client-context? ssl-server-context?)
   = 
((if (eq? mode 'accept)
     ssl-make-server-context
     ssl-make-client-context)
 protocol)
  protocol : symbol? = 'sslv2-or-v3
  close-original? : boolean? = #f
  shutdown-on-close? : boolean? = #f
  error : procedure? = error

Returns two values – an input port and an output port – that implement the SSL protocol over the given input and output port. (The given ports should be connected to another process that runs the SSL protocol.)

The mode argument can be 'connect or 'accept. The mode determines how the SSL protocol is initialized over the ports, either as a client or as a server. As with ssl-listen, in 'accept mode, supply a context that has been initialized with ssl-load-certificate-chain! and ssl-load-private-key! to avoid a no shared cipher error.

The context argument should be a client context for 'connect mode or a server context for 'accept mode. If it is not supplied, a context is created using the protocol specified by a protocol argument.

If the protocol argument is not supplied, it defaults to 'sslv2-or-v3. See ssl-make-client-context for further details (including all options and the meanings of the protocol symbols). This argument is ignored if a context argument is supplied.

If close-original? is true, then when both SSL ports are closed, the given input and output ports are automatically closed. The default is #f.

If shutdown-on-close? is true, then when the output SSL port is closed, it sends a shutdown message to the other end of the SSL connection. The default is #f. When shutdown is enabled, closing the output port can fail if the given output port becomes unwritable (e.g., because the other end of the given port has been closed by another process).

The error argument is an error procedure to use for raising communication errors. The default is error, which raises exn:fail; in contrast, ssl-accept and ssl-connect use an error function that raises exn:fail:network.

See also ssl-connect about the limitations of reading and writing to an SSL connection (i.e., one direction at a time).

4 Context Procedures

(ssl-load-certificate-chain! context-or-listener    
  pathname)  void?
  context-or-listener : 
(or/c ssl-client-context? ssl-server-context?
      ssl-listener?)
  pathname : path-string?

Loads a PEM-format certification chain file for connections to made with the given context (created by ssl-make-client-context or ssl-make-server-context) or listener (created by ssl-listen).

This chain is used to identify the client or server when it connects or accepts connections. Loading a chain overwrites the old chain. Also call ssl-load-private-key! to load the certificate’s corresponding key.

You can use the file "test.pem" of the "openssl" collection for testing purposes. Since "test.pem" is public, such a test configuration obviously provides no security.

(ssl-load-private-key! context-or-listener    
  pathname    
  [rsa?    
  asn1?])  void?
  context-or-listener : 
(or/c ssl-client-context? ssl-server-context?
      ssl-listener?)
  pathname : path-string?
  rsa? : boolean? = #t
  asn1? : boolean? = #f

Loads the first private key from pathname for the given context or listener. The key goes with the certificate that identifies the client or server.

If rsa? is #t (the default), the first RSA key is read (i.e., non-RSA keys are skipped). If asn1? is #t (the default is #f), the file is parsed as ASN1 format instead of PEM.

You can use the file "test.pem" of the "openssl" collection for testing purposes. Since "test.pem" is public, such a test configuration obviously provides no security.

(ssl-set-verify! context-or-listener    
  verify?)  void?
  context-or-listener : 
(or/c ssl-client-context? ssl-server-context?
       ssl-listener?)
  verify? : boolean?

Enables or disables verification of a connection peer’s certificates. By default, verification is disabled.

Enabling verification also requires, at a minimum, designating trusted certificate authorities with ssl-load-verify-root-certificates!.

(ssl-load-verify-root-certificates! context-or-listener 
  pathname) 
  void?
  context-or-listener : 
(or/c ssl-client-context? ssl-server-context?
       ssl-listener?)
  pathname : path-string?

Loads a PEM-format file containing trusted certificates that are used to verify the certificates of a connection peer. Call this procedure multiple times to load multiple sets of trusted certificates.

You can use the file "test.pem" of the "openssl" collection for testing purposes. Since "test.pem" is public, such a test configuration obviously provides no security.

(ssl-load-suggested-certificate-authorities! 
  context-or-listener 
  pathname) 
  void?
  context-or-listener : 
(or/c ssl-client-context? ssl-server-context?
       ssl-listener?)
  pathname : path-string?

Loads a PEM-format file containing certificates that are used by a server. The certificate list is sent to a client when the server requests a certificate as an indication of which certificates the server trusts.

Loading the suggested certificates does not imply trust, however; any certificate presented by the client will be checked using the trusted roots loaded by ssl-load-verify-root-certificates!.

You can use the file "test.pem" of the "openssl" collection for testing purposes where the peer identifies itself using "test.pem".

5 Implementation Notes

For Windows, openssl relies on "libeay32.dll" and "ssleay32.dll", where the DLLs are located in the same place as "libmzsch‹vers›.dll" (where ‹vers› is either xxxxxxx or a mangling of PLT Scheme’s version number). The DLLs are distributed as part of PLT Scheme.

For Unix variants, openssl relies on "libcryto.so" and "libssl.so", which must be installed in a standard library location, or in a directory listed by LD_LIBRARY_PATH.

For Mac OS X, openssl relies on "libssl.dylib" and "libcryto.dylib", which are part of the OS distribution for Mac OS X 10.2 and later.