This is a crackme from http://crackmes.de/. It is a elf64 compiled on Gentoo in 2004. The crackme is solved and it is fairly easy one. However things have changed in Linux for the last 13 years. There is incompatibility between current libc versions used then and now. The resurection of the executable under modern Ubuntu was even more interesting then the crackme itself.
This was easy one.
However, I spent some time researching ELF format in order to fix its sections. This is a very old crackme and it won't start on modern Linux distribution. I had to patch first the .dynsym section before moving ahead.
The "protection" is a check after ptrace call which is easily patched.
$ cd write-ups/challenges/crackmes.de@64bit_Confusion
$ make
...
$ ./64bit_Confusion.patched `cat key.txt`
You have entered: 8675309
You have CRACKED me! Congratulations!