Update: Just use VeraCrypt: https://www.veracrypt.fr/en/Downloads.html Its an actively maintained fork of Truecrypt 7.1a
Despite the suspicious shutdown of Truecrypt, it is still a solid solution for your data encryption needs unless you are an enemy of state. Installing the last usable version on Truecrypt (7.1a) requires some tribal knowledge to install on OSX Yosemite. Here is how to bypass the “TrueCrypt requires Mac OS X 10.4 or later.” error:
1) Double-click truecrypt_7.1a_mac_os_x.dmg
2) Right-click TrueCrypt_7.1a.mpkg and “Show Package Contents”
3) Open Contents Dir
4) Open Packages Dir
5) Install OSXFUSECore.pkg
6) Install OSXFUSEMacFUSE.pkg
7) Install MacFUSE.pkg
8) Install TrueCrypt.pkg