► |  | Open SSL: Secure Communication

1 | TCP-like Client Procedures
2 | TCP-like Server Procedures
3 | SSL-wrapper Interface
4 | Context Procedures
5 | Peer Verification
6 | SHA-1 Hashing

ssl-available?
ssl-load-fail-reason
1`` TCP-like Client Procedures
ssl-connect
ssl-connect/ enable-break
ssl-secure-client-context
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-abandon-port
ssl-addresses
ssl-port?
ssl-make-server-context
ssl-server-context?
3`` SSL-wrapper Interface
ports->ssl-ports
4`` Context Procedures
ssl-load-verify-source!
ssl-default-verify-sources
ssl-load-default-verify-sources!
ssl-load-verify-root-certificates!
ssl-set-ciphers!
ssl-seal-context!
ssl-load-certificate-chain!
ssl-load-private-key!
ssl-load-suggested-certificate-authorities!
5`` Peer Verification
ssl-set-verify!
ssl-try-verify!
ssl-peer-verified?
ssl-set-verify-hostname!
ssl-peer-certificate-hostnames
ssl-peer-check-hostname
ssl-peer-subject-name
ssl-peer-issuer-name
6`` SHA-1 Hashing
sha1
sha1-bytes
bytes->hex-string

5.3.6
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## OpenSSL: Secure Communication

(require openssl)

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

To use this library, you will need OpenSSL installed on your machine, but on many platforms the necessary libraries are included with the OS or with the Racket distribution. In particular:

- For Windows, openssl depends on "libeay32.dll" and "ssleay32.dll", which are included in the Racket distribution for Windows.

- For Mac OS X, openssl depends on "libssl.dylib" and "libcrypto.dylib", which are provided by Mac OS X 10.2 and later.

- For Unix, openssl depends on "libssl.so" and "libcrypto.so", which must be installed in a standard library location or in a directory listed by LD_LIBRARY_PATH. These libraries are included in many OS distributions.

> value 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.

> value ssl-load-fail-reason : (or/c #f string?)

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

### 1`` TCP-like Client Procedures

Use ssl-connect or ssl-connect/enable-break to create an SSL connection over TCP. To create a secure connection, supply the result of ssl-secure-client-context or create a client context with ssl-make-client-context and configure it using the functions described in Context Procedures.

> > procedure
> > (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?
> 'sslv2-or-v3
> 'sslv2
> 'sslv3
> 'tls)
> |  | = |  | '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.

If hostname verification is enabled (see ssl-set-verify-hostname!), the peer’s certificate is checked against hostname.

> > procedure
> > (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? 'sslv2-or-v3 'sslv2 'sslv3 'tls)
> |  |  | = |  | 'sslv2-or-v3

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

> procedure (ssl-secure-client-context) → ssl-client-context?

Returns a client context (using the 'tls protocol) that verifies certificates using the default verification sources from (ssl-default-verify-sources), verifies hostnames, and avoids using weak ciphers. The result is essentially equivalent to the following:

> (let ([ctx (ssl-make-client-context 'tls)])
> ; Load default verification sources (root certificates)
> (ssl-load-default-verify-sources! ctx)
> ; Require certificate verification
> (ssl-set-verify! ctx #t)
> ; Require hostname verification
> (ssl-set-verify-hostname! ctx #t)
> ; No weak cipher suites
> (ssl-set-ciphers! ctx "DEFAULT:!aNULL:!eNULL:!LOW:!EXPORT:!SSLv2")
> ; Seal context so further changes cannot weaken it
> (ssl-seal-context! ctx)
> ctx)

The context is cached, so different calls to ssl-secure-client-context return the same context unless (ssl-default-verify-sources) has changed.

> procedure (ssl-make-client-context [protocol]) → ssl-client-context?
> | protocol |  | : |  | (or/c 'sslv2-or-v3 'sslv2 'sslv3 'tls)
> |  |  | = |  | '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:

- 'sslv2-or-v3 : SSL protocol versions 2 or 3, as appropriate (this is the default)

- 'sslv2 : SSL protocol version 2

- 'sslv3 : SSL protocol version 3

- 'tls : the TLS protocol version 1

Note that SSL protocol version 2 is deprecated on some platforms and may not be present in your system libraries. The use of SSLv2 may also compromise security; thus, using SSLv3 is recommended.

> procedure (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

> > procedure
> > (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? = 5
> reuse? : any/c = #f
> hostname-or-#f : (or/c string? #f) = #f
> | server-protocol |  | : |  | (or/c ssl-server-context? 'sslv2-or-v3 'sslv2 'sslv3 'tls)
> |  |  | = |  | 'sslv2-or-v3

Like tcp-listen, but the result is an SSL listener. 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.

An SSL listener is a synchronizable value (see sync). It is ready—with itself as its value—when the underlying TCP listener is ready. At that point, however, accepting a connection with ssl-accept may not complete immediately, because further communication is needed to establish the connection.

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

Analogous to tcp-close and tcp-listener?.

> > procedure
> > (ssl-accept listener) |  | → |  |
> > input-port? |  | output-port?
> listener : ssl-listener?
> > procedure
> > (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.

> procedure (ssl-abandon-port in) → void?
> in : (and/c ssl-port? output-port?)

Analogous to tcp-abandon-port.

> procedure (ssl-addresses p [port-numbers?]) → void?
> p : (or/c ssl-port? ssl-listener?)
> port-numbers? : any/c = #f

Analogous to tcp-addresses.

> procedure (ssl-port? v) → boolean?
> v : any/c

Returns #t of v is an SSL port produced by ssl-connect, ssl-connect/enable-break, ssl-accept, ssl-accept/enable-break, or ports->ssl-ports.

> procedure (ssl-make-server-context protocol) → ssl-server-context?
> protocol : (or/c 'sslv2-or-v3 'sslv2 'sslv3 'tls)

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

> procedure (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

> > procedure
> > (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 |
> > |  | #:hostname hostname]) |
> | → |  |
> 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 |  | : |  | (or/c 'sslv2-or-v3 'sslv2 'sslv3 'tls)
> |  |  | = |  | 'sslv2-or-v3
> close-original? : boolean? = #f
> shutdown-on-close? : boolean? = #f
> error : procedure? = error
> hostname : (or/c string? #f) = #f

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.

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. 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).

If hostname verification is enabled (see ssl-set-verify-hostname!), the peer’s certificate is checked against hostname.

### 4`` Context Procedures

> > procedure
> > (ssl-load-verify-source! |  | context |  |  |  |
> > |  | src |  |  |  |
> > | [ | #:try? try?]) |  | → |  | void?
> context : (or/c ssl-client-context? ssl-server-context?)
> | src |  | : |  |
> (or/c path-string?
> (list/c 'directory path-string?)
> (list/c 'win32-store string?)
> (list/c 'macosx-keychain path-string?))
> try? : any/c = #f

Loads verification sources from src into context. Currently, only certificates are loaded; the certificates are used to verify the certificates of a connection peer. Call this procedure multiple times to load multiple sets of trusted certificates.

The following kinds of verification sources are supported:

- If src is a path or string, it is treated as a PEM file containing root certificates. The file is loaded immediately.

- If src is (list 'directory dir), then dir should contain PEM files with hashed symbolic links (see the openssl c_rehash utility). The directory contents are not loaded immediately; rather, they are searched only when a certificate needs verification.

- If src is (list 'win32-store store), then the certificates from the store named store are loaded immediately. Only supported on Windows.

- If src is (list 'macosx-keychain path), then the certificates from the keychain stored at path are loaded immediately. Only supported on Mac OS X.

If try? is #f and loading src fails (for example, because the file or directory does not exist), then an exception is raised. If try? is a true value, then a load failure is ignored.

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.

> parameter (ssl-default-verify-sources)
> | → |  |
> (let ([source/c (or/c path-string?
> (list/c 'directory path-string?)
> (list/c 'win32-store string?)
> (list/c 'macosx-keychain path-string?))])
> (listof source/c))
> (ssl-default-verify-sources srcs) → void?
> | srcs |  | : |  |
> (let ([source/c (or/c path-string?
> (list/c 'directory path-string?)
> (list/c 'win32-store string?)
> (list/c 'macosx-keychain path-string?))])
> (listof source/c))

Holds a list of verification sources, used by ssl-load-default-verify-sources!. The default sources depend on the platform:

- On Linux, the default sources are determined by the SSL_CERT_FILE and SSL_CERT_DIR environment variables, if the variables are set, or the system-wide default locations otherwise.

- On Mac OS X, the default sources consist of the system keychain for root certificates: '(macosx-keychain "/System/Library/Keychains/SystemRootCertificates.keychain").

- On Windows, the default sources consist of the system certificate store for root certificates: '(win32-store "ROOT").

> procedure (ssl-load-default-verify-sources! context) → void?
> context : (or/c ssl-client-context? ssl-server-context?)

Loads the default verification sources, as determined by (ssl-default-verify-sources), into context. Load failures are ignored, since some default sources may refer to nonexistent paths.

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

Deprecated; like ssl-load-verify-source!, but only supports loading certificate files in PEM format.

> procedure (ssl-set-ciphers! context cipher-spec) → void?
> context : (or/c ssl-client-context? ssl-server-context?)
> cipher-spec : string?

Specifies the cipher suites that can be used in connections created with context. The meaning of cipher-spec is the same as for the openssl ciphers command.

> procedure (ssl-seal-context! context) → void?
> context : (or/c ssl-client-context? ssl-server-context?)

Seals context, preventing further modifications. After a context is sealed, passing it to functions such as ssl-set-verify! and ssl-load-verify-root-certificates! results in an error.

> > procedure
> > (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 server context (created by ssl-make-server-context) or listener (created by ssl-listen). A certificate chain can also be loaded into a client context (created by ssl-make-client-context) when connecting to a server requiring client credentials, but that situation is uncommon.

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.

> > procedure
> > (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. Like ssl-load-certificate-chain!, this procedure is usually used with server contexts or listeners, seldom with client contexts.

If rsa? is #t (the default), 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.

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.

> > procedure
> > (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`` Peer Verification

> procedure (ssl-set-verify! clp on?) → void?
> | clp |  | : |  |
> (or/c ssl-client-context? ssl-server-context?
> ssl-listener? ssl-port?)
> on? : any/c

Requires certificate verification on the peer SSL connection when on? is #t. If clp is an SSL port, then the connection is immediately renegotiated, and an exception is raised immediately if certificate verification fails. If clp is a context or listener, certification verification happens on each subsequent connection using the context or listener.

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

Verifying the certificate is not sufficient to prevent attacks by active adversaries, such as man-in-the-middle attacks. See also ssl-set-verify-hostname!.

> procedure (ssl-try-verify! clp on?) → void?
> | clp |  | : |  |
> (or/c ssl-client-context? ssl-server-context?
> ssl-listener? ssl-port?)
> on? : any/c

Like ssl-set-verify!, but when peer certificate verification fails, then connection continues to work. Use ssl-peer-verified? to determine whether verification succeeded.

> procedure (ssl-peer-verified? p) → boolean?
> p : ssl-port?

Returns #t if the peer of SSL port p has presented a valid and verified certificate, #f otherwise.

> procedure (ssl-set-verify-hostname! ctx on?) → void?
> ctx : (or/c ssl-client-context? ssl-server-context?)
> on? : any/c

Requires hostname verification of SSL peers of connections made using ctx when on? is #t. When hostname verification is enabled, the hostname associated with a connection (see ssl-connect or ports->ssl-ports) is checked against the hostnames listed in the peer’s certificate. If the peer certificate does not contain an entry matching the hostname, or if the peer does not present a certificate, the connection is rejected and an exception is raised.

Hostname verification does not imply certificate verification. To verify the certificate itself, also call ssl-set-verify!.

> procedure (ssl-peer-certificate-hostnames p) → (listof string?)
> p : ssl-port?

Returns the list of hostnames for which the certificate of p’s peer is valid according to RFC 2818. If the peer has not presented a certificate, '() is returned.

The result list may contain both hostnames such as "www.racket-lang.org" and hostname patterns such as "*.racket-lang.org".

> procedure (ssl-peer-check-hostname p hostname) → boolean?
> p : ssl-port?
> hostname : string?

Returns #t if the peer certificate of p is valid for hostname according to RFC 2818.

> procedure (ssl-peer-subject-name p) → (or/c bytes? #f)
> p : ssl-port?

If ssl-peer-verified? would return #t for p, the result is a byte string for the subject field of the certificate presented by the SSL port’s peer, otherwise the result is #f.

Use ssl-peer-check-hostname or ssl-peer-certificate-hostnames instead to check the validity of an SSL connection.

> procedure (ssl-peer-issuer-name p) → (or/c bytes? #f)
> p : ssl-port?

If ssl-peer-verified? would return #t for p, the result is a byte string for the issuer field of the certificate presented by the SSL port’s peer, otherwise the result is #f.

### 6`` SHA-1 Hashing

(require openssl/sha1)

The openssl/sha1 library provides a Racket wrapper for the OpenSSL library’s SHA-1 hashing functions. If the OpenSSL library cannot be opened, this library logs a warning and falls back to the implementation in file/sha1.

> procedure (sha1 in) → string?
> in : input-port?

Returns a 40-character string that represents the SHA-1 hash (in hexadecimal notation) of the content from in, consuming all of the input from in until an end-of-file.

The sha1 function composes bytes->hex-string with sha1-bytes.

> procedure (sha1-bytes in) → bytes?
> in : input-port?

Returns a 20-byte byte string that represents the SHA-1 hash of the content from in, consuming all of the input from in until an end-of-file.

> procedure (bytes->hex-string bstr) → string?
> bstr : bytes?

Converts the given byte string to a string representation, where each byte in bstr is converted to its two-digit hexadecimal representation in the resulting string.
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