Someone at Microsoft just turned me on to this cool site. www.keylength.comThe site lists various standards and their recommended crypto sizes. You can click on any listed crypto algorithm and see how long a crypto key of that size should remain relatively protective. It's all generic and doesn't include a large number of external factors that would impact the key's overall useful life, but it is a starting point for reference.I frequently have customers and readers ask me how long their key size should be for a particular application. It's like asking what car someone should buy? There's a lot of factors involved, with no single answer. In order to determine how long a particular cypto key should be you need to ask yourself many other questions first, including:What is the value of the information you are protecting?What is the security maturity of the company expecting the protection?What is the likelihood of a sustained, multi-machine crack attack?What are the regulatory requirements?How often are the keys changed? What cipher is used?Crypto ciphers are just one mechanism to prevent a confidentiality leak. What other protections do you use? How is the information protected from physical attack? Is the cipher algorithm protection mechanism implemented in hardware or software?And so on.