In several places, TMP_ALLOC is used with potentially large arguments. This can cause a stack overflow. Functions taking key_size arguments (e.g., pkcs1_decrypt, pkcs1_encrypt, pkcs1_rsa_digest_encode, ...) and nettle_mpz_random_size are affected.
nettle-2.7.1-3.fc20 has been submitted as an update for Fedora 20. https://admin.fedoraproject.org/updates/nettle-2.7.1-3.fc20
Package nettle-2.7.1-3.fc20: * should fix your issue, * was pushed to the Fedora 20 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing nettle-2.7.1-3.fc20' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2014-0613/nettle-2.7.1-3.fc20 then log in and leave karma (feedback).
nettle-2.7.1-3.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.