When Alice wants to send an encrypted message to Bob, she must use:

  1. Bob’s public key to encrypt a message for him;
  2. Her (Alice’s) private key to sign the message;
  3. Her public key to decrypt own messages (to have an opportunity to read her encrypted message later). 

Then Bob must use:

  1. His private key to decrypt an encrypted message from Alice;
  2. Alice’s public key to verify her signature (that it’s really a message from Alice).
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