[KhalilK]

For an n-bit RSA key "The absolute minimum size for n is 2048 bits or so if you want to protect your data for 20 years. [...] If you can afford it in your application, let n be 4096 bits long, or as close to this size as you can get it."

http://www.javamex.com/tutorials/cryptography/rsa_key_length...