From: http://www.x2on.de/2010/02/01/tutorial-iphone-app-with-compiled-openssl-library/

UPDATE 2010-03-31: I have updated OpenSSL to 0.9.8n
UPDATE 2010-02-26: I have updated OpenSSL to 0.9.8m

This is a tutorial for using self-compiled builds of  the OpenSSL-library on the iPhone. You can build apps with XCode and the official SDK from Apple with this. I also made a small example-app for using the libraries with XCode and the iPhone/iPhone-Simulator. You can also download the precompiled OpenSSL-library (0.9.8n).

Create OpenSSL Libary:

    * Download OpenSSL Sourcecode
    * Build OpenSSL for i368 iPhoneSimulator:
          o cd openssl-0.9.8n
            mkdir openssl_arm
            mkdir openssl_i386
            ./config --openssldir=/PathtoOpenSSL/openssl_i386

          o Edit Makefile:
                + Change CC = cc to:

                  CC= /Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/gcc-4.0

                + Add as first item to CFLAG:

                  -isysroot /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.3.sdk

          o Change in crypto/ui/ui_openssl.c

            static volatile sig_atomic_t intr_signal;

            to

            static volatile int intr_signal;

            for preventing building error
          o Build it:

            make
            make install

          o Your libcrypto.a and libssl.a are in the folder openssl_i368/lib
          o Rename the two files to libcrypto_i386.a and libssl_i386.a
    * Build OpenSSL for arm iPhoneOS:
          o Edit Makefile:
                + Search and replace openssl_i386 with openssl_arm
                + Change -arch i386 in CFLAG to:
                  -arch armv6
                + Change

                  CC=  /Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/gcc-4.0

                  to

                  CC=  /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.0

                + Change

                  -isysroot  /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.3.sdk

                  to

                  -isysroot  /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.3.sdk

          o Build it:
            make
            make install

          o Your libcrypto.a and libssl.a are in the folder openssl_arm/lib
          o Rename the two files to libcrypto_arm.a and libssl_arm.a

Edit your iPhone-XCode project:

    * Copy the “include” folder from OpenSSL into your project-folder
    * Copy the libcrypto_*.a and libss_*.a files into your project-folder
    * Drag the libcrypto_*.a and libss_*.a files into your XCode Framework Folder-Tree
    * Open the Build-Info from your “Target” (Righclick on Target – Get Info)
    * Change Library Search Paths to

      $(inherited) "$(SRCROOT)"

    * Change User Header Search Paths to include
    * Activate Always Search User Paths

Enjoy OpenSSL on the iPhone!

I have made an iPhone OS 3.1.3 XCode Project with OpenSSL 0.9.8n Libaries. The examples uses the MD5-algorithm to calculate an md5 hash from an UITextfield.