title: gnupg gives me the error "Invalid public key algorithm" when I try to use an old key
body: <p>When I try to decrypt an old file, gpg2 gives me this error:</p>
  
  <pre><code>gpg: public key decryption failed: Invalid public key algorithm
  gpg: decryption failed: No secret key
  </code></pre>
  
  <p>gpg1 gives me this error:</p>
  
  <pre><code>gpg: Ohhhh jeeee: no decrypt() for 17
  secmem usage: 1664/2432 bytes in 5/8 blocks of pool 2432/32768
  Abort trap: 6
  </code></pre>