I just spent a few hours trying to figure out why my RSA encryption stopped working on iOS. The problem was that I had added sha1.c source for some unrelated functionality I was testing on OSX. That duplicated some of the functions in the OpenSSL library that I am statically linking to for the RSA encryption, which caused the RSA encryption to malfunction. I thought this was supposed to generate a duplicate symbol warning? I do not see a setting for that under Linker build settings.