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How to add a crypto library

PicoSOCKS5 can be compiled with GnuTLS or OpenSSL, and even without any crypto library at all. To compile PicoSOCKS5 with a new crypto library you have to perform two tasks:

  1. Write a wrapper for the library.
  2. Integrate the wrapper into the configure script.

First, you have to decide following parameters:

  • Choose a unique name ("module name") by which the crypto library will be known in the configuration script. Lower case and no spaces is the preferred format. Names "yes", "no", "emul", "gnutls", and "openssl" must not be used.
  • Choose a list of options that must be passed to the compiler when linking with the library.

Writing a wrapper

  • Crypto library wrapper is a C source file, which is included into file src/crypto.c. It may omit some includes that are already made in the including file.
  • The wrapper source file must reside in src/ and its name must have format crypto-NAME.c, where NAME is the chosen crypto module name.
  • The wrapper must implement methods crypto_init, crypto_generate_nonce, and crypto_hmac_md5. Signatures for these methods are specified in file src/crypto.h.

For reference look at the implemented wrappers (src/crypto-gnutls.c and src/crypto-openssl.c).

Integrating into configuration script

To integrate your wrapper into the configure script, you have to add corresponding autoconf tests into configure.ac. The place that has to be modified can be found between comments ### ADD CUSTOM CRYPTO MODULES BELOW and ### END OF CUSTOM CRYPTO MODULES.

For inspiration look at GnuTLS and OpenSSL module blocks above the comments.

Your code must check that your crypto module was chosen, check whether the library you need is installed, and set following variables:

  • CRYPTO_MODULE is set to your crypto module name.
  • CRYPTO_LIBS must be set to additional compiler options needed for linking.

In the example below:

  • The crypto module name is my_lib.
  • Linking requires compiler option -lmy_lib_name, and the library has function my_lib_function that can be used for library detection.
AS_IF([test -z "$CRYPTO_MODULE" -a \( "x$want_crypto" = xyes -o "x$want_crypto" = xmy_lib \)],
      [AC_MSG_NOTICE([checking for MyLib crypto module])
       AC_CHECK_LIB([my_lib_name], [my_lib_function],
                    [CRYPTO_MODULE="my_lib"
                     CRYPTO_LIBS="-lmy_lib_name"])
      ])