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openssl

Description

Bindings to the OpenSSL SSL/TLS library

Author

Thomas Chust

Requirements

None, except for the openssl C library of course.

Documentation

This reference is basically a copy of the documentation of PLT Scheme's openssl module. The API provided here is largely compatible with that one. The exceptions are the missing .../enable-break and ssl-available? procedures and the missing reuse? argument to ssl-listen.

Please note that all the procedures described here may fail and raise a non-continuable exception of the composite type (exn i/o net openssl). The openssl property condition contains a property called status which will be bound to a symbol corresponding to the OpenSSL error code that was encountered. It may have the following values:

'zero-return
The SSL/TLS connection was shut down unexpectedly but in a controlled way
'want-read
The operation didn't finish because data must be read from a nonblocking socket. This error condition only occurs though, when it could not be handled automatically because there is actually no socket involved or some other strange thing happended in the OpenSSL library.
'want-write
The operation didn't finish because data must be read from a nonblocking socket. The same comment as for 'want-read applies.
'want-connect
The operation didn't finish because a nonblocking socket must first be connected. The same comment as for 'want-read applies.
'want-accept
The operation didn't finish because a nonblocking socket must first be acepted. The same comment as for 'want-read applies.
'want-X509-lookup
The operation failed because an application callback that could not even have been registered through this API was apparently registered anyway and has asked to be called again.
'syscall
Some low-level I/O error occurred.
'ssl
Something went wrong in the OpenSSL library itself.
#f
The error is not classified

Of course the exception that is thrown also has an appropriate message set. If you feel that this documentation lacks some information, please also consider the manual pages of OpenSSL itself.

Global parameters

For read and write timeouts, tcp-read-timeout and tcp-write-timeout are honored.

(ssl-handshake-timeout [TIMEOUT]) parameter

The time in milliseconds to wait for a SSL handshake to complete (after ssl-connect or ssl-accept). Defaults to 120000, ie two minutes.

note: The handshake is only initiated after the first read or the first write action occurs on the connection, so the timer is started upon that first action.

(ssl-shutdown-timeout [TIMEOUT]) parameter

The time in milliseconds to wait for a SSL shutdown operation to complete (after closing a port). Defaults to 120000, ie two minutes.

Client procedures
(ssl-connect (hostname <string>) #!optional (port <exact>) ((ctx <ssl-client-context|symbol>) 'sslv2-or-v3)) => <input-port>, <output-port> procedure

Connect to the given host on the given port (a number from 1 to 65535). This connection will be encrypted using SSL. The return values are as tcp-connect; an input port and an output port.

The optional ctx 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 (see below), 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.

(ssl-make-client-context #!optional ((protocol <symbol>) 'sslv2-or-v3)) => <ssl-client-context> procedure

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 "Certificate procedures" section below for more information on certificates.

The protocol must be one of the following:

'sslv2-or-v3
SSL protocol versions 2 or 3, as appropriate
'sslv2
SSL protocol version 2
'sslv3
SSL protocol version 3
'tls
the TLS protocol version 1

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? (obj <top>)) => <bool> procedure

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

Server procedures

(ssl-listen (port <exact>) #!optional ((backlog <exact>) 4) ((hostname <string>) #f) ((ctx <ssl-client-context|symbol>) 'sslv2-or-v3)) => <ssl-listener> procedure

Like tcp-listen, but the result is an SSL listener. The extra optional ctx argument is as for ssl-connect.

Call ssl-load-certificate-chain! and ssl-load-private-key! to avoid a "no shared cipher" error on accepting connections.

(ssl-close (listener <ssl-listener>)) => <void> procedure
(ssl-listener? (obj <top>)) => <bool> procedure
(ssl-listener-port (listener <ssl-listener>)) => <exact> procedure
(ssl-listener-fileno (listener <ssl-listener>)) => <exact> procedure
(ssl-listener-accept-ready? (listener <ssl-listener>)) => <bool> procedure
(ssl-accept (listener <ssl-listener>)) => <input-port>, <output-port> procedure

Analogous to tcp-close, tcp-listener?, tcp-listener-port, tcp-listener-fileno, tcp-accept-ready? and tcp-accept.

Certificate procedures

(ssl-load-certificate-chain! (obj <ssl-client-context|ssl-listener>) (pathname <string>)) => <void> procedure

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

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.

(ssl-load-private-key! (obj <ssl-client-context|ssl-listener>) (pathname <string>) #!optional ((rsa? <bool>) #t) ((asn1? <bool>) #f)) => <void> procedure

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

If rsa? is #t, the first RSA key is read (i.e., non-RSA keys are skipped).

If asn1? is #t, the file is parsed as ASN1 format instead of PEM.

(ssl-set-verify! (obj <ssl-client-context|ssl-listener>) (v <bool>)) => <void> procedure

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! (obj <ssl-client-context|ssl-listener>) (pathname <string>) #!optional ((dirname <string>) #f)) => <void> procedure

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.

The optional second argument specifies a directory in which certificates are automatically looked up. You may also only pass a path in this argument and pass #f as the first argument to this procedure. See the OpenSSL documentation on SSL_CTX_load_verify_locations for more details.

(ssl-load-suggested-certificate-authorities! (obj <ssl-client-context|ssl-listener>) (pathname <string>)) => <void> procedure

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!.

Port procedures

(ssl-port? obj) => <boolean> procedure

Predicate for SSL ports; returns #t if obj is an SSL port, #f if it isn't.

(ssl-port->tcp-port p) => <tcp-port> procedure

Convert SSL port p to the raw underlying TCP port.

This is mostly useful if you need to obtain extra information about the connection, like for example tcp-addresses. Note that you generally cannot safely send data over the port, as that would interfere with OpenSSL's operation.

Changelog

License

 Copyright (c) 2005, Thomas Chust <chust@web.de>.  All rights reserved.
 
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