title: Load RSA private key from a PEM encoded private key
body: <p>I'm trying to load an RSA private key from a <code>std::string</code> that contains the private key in PEM format, like this: </p>
  
  <pre><code>-----BEGIN RSA PRIVATE KEY-----
  MIIBOgIBAAJBAK8Q+ToR4tWGshaKYRHKJ3ZmMUF6jjwCS/u1A8v1tFbQiVpBlxYB
  paNcT2ENEXBGdmWqr8VwSl0NBIKyq4p0rhsCAQMCQHS1+3wL7I5ZzA8G62Exb6RE
  INZRtCgBh/0jV91OeDnfQUc07SE6vs31J8m7qw/rxeB3E9h6oGi9IVRebVO+9zsC
  IQDWb//KAzrSOo0P0yktnY57UF9Q3Y26rulWI6LqpsxZDwIhAND/cmlg7rUz34Pf
  SmM61lJEmMEjKp8RB/xgghzmCeI1AiEAjvVVMVd8jCcItTdwyRO0UjWU4JOz0cnw
  5BfB8cSIO18CIQCLVPbw60nOIpUClNxCJzmMLbsrbMcUtgVS6wFomVvsIwIhAK+A
  YqT6WwsMW2On5l9di+RPzhDT1QdGyTI5eFNS+GxY
  -----END RSA PRIVATE KEY-----
  </code></pre>
  
  <p>And I wonder if anyone can help me to use this key instead of generating a random with the following statement. </p>
  
  <pre><code>CryptoPP::RSA::PrivateKey rsaPrivate; 
  rsaPrivate.GenerateRandomWithKeySize (rnd, 512);
  </code></pre>