<DRAFT!> OpenSSL 有关密钥的那些事儿（HOWTO keys） 1. 介绍（Introduction） Keys are the basis of public key algorithms and PKI. Keys usually come in pairs, with one half being the public key and the other half being the private key. With OpenSSL, the private key contains the public key information as well, so a public key doesn't need to be generated separately. Public keys come in several flavors, using different cryptographic algorithms. The most popular ones associated with certificates are RSA and DSA, and this HOWTO will show how to generate each of them. 2. 生成 RSA 密钥（To generate a RSA key） A RSA key can be used both for encryption and for signing. Generating a key for the RSA algorithm is quite easy, all you have to do is the following: openssl genrsa -des3 -out privkey.pem 2048 With this variant, you will be prompted for a protecting password. If you don't want your key to be protected by a password, remove the flag '-des3' from the command line above. NOTE: if you intend to use the key together with a server certificate, it may be a good thing to avoid protecting it with a password, since that would mean someone would have to type in the password every time the server needs to access the key. The number 2048 is the size of the key, in bits. Today, 2048 or higher is recommended for RSA keys, as fewer amount of bits is consider insecure or to be insecure pretty soon. 3. 生成 DSA 密钥（To generate a DSA key） A DSA key can be used for signing only. This is important to keep in mind to know what kind of purposes a certificate request with a DSA key can really be used for. Generating a key for the DSA algorithm is a two-step process. First, you have to generate parameters from which to generate the key: openssl dsaparam -out dsaparam.pem 2048 The number 2048 is the size of the key, in bits. Today, 2048 or higher is recommended for DSA keys, as fewer amount of bits is consider insecure or to be insecure pretty soon. When that is done, you can generate a key using the parameters in question (actually, several keys can be generated from the same parameters): openssl gendsa -des3 -out privkey.pem dsaparam.pem With this variant, you will be prompted for a protecting password. If you don't want your key to be protected by a password, remove the flag '-des3' from the command line above. NOTE: if you intend to use the key together with a server certificate, it may be a good thing to avoid protecting it with a password, since that would mean someone would have to type in the password every time the server needs to access the key. -- Richard Levitte