Create a private key-pair and encrypt it for use in .travis.yml with working code for decrypting it on both linux and osx builders

travis_secure_private_key.sh

#!/bin/bash

ssh-keygen -t rsa -N "" -C travis -f ./travis_key

# i only tested the encrypting on Linux.
# on mac you need gsplit instead of split, but the rest should be mostly the same
# 
# decryption works on both linux and mac travis-workers

echo "encrypt private"
base64 --wrap=0 ./travis_key > ./travis_key_base64
ENCRYPTION_FILTER="echo \$(echo \"    - secure: \")\$(travis encrypt \"\$FILE='\`cat $FILE\`'\" -r koter84/tg)"
split --bytes=100 --numeric-suffixes --suffix-length=2 --filter="$ENCRYPTION_FILTER" ./travis_key_base64 id_rsa_

echo "encrypt public"
base64 --wrap=0 ./travis_key.pub > ./travis_key_base64.pub
ENCRYPTION_FILTER="echo \$(echo \"    - secure: \")\$(travis encrypt \"\$FILE='\`cat $FILE\`'\" -r koter84/tg)"
split --bytes=100 --numeric-suffixes --suffix-length=2 --filter="$ENCRYPTION_FILTER" ./travis_key_base64.pub id_rsa_pub_

## The parts below go in the .travis.yml file, and work on linux and osx hosts

- echo "decrypt private"
- for i in {0..30}; do eval $(printf "echo \$id_rsa_%02d\n" $i) >> ~/.ssh/id_rsa_base64; done
- base64 --decode ~/.ssh/id_rsa_base64 > ~/.ssh/id_rsa
- chmod 600 ~/.ssh/id_rsa

- echo "decrypt public"
- for i in {0..10}; do eval $(printf "echo \$id_rsa_pub_%02d\n" $i) >> ~/.ssh/id_rsa_base64.pub; done
- base64 --decode ~/.ssh/id_rsa_base64.pub > ~/.ssh/id_rsa.pub
- chmod 600 ~/.ssh/id_rsa.pub