In this illustration, we see Bob looking rightward. A blue arrow points rightward from Bob and his key, labeled (K (+/B, B), to a blue box labeled "Encryption algorithm." Above the algorithm is CA's private key, K (-/CA); a blue arrow points downward from the key to the algorithm. A label to the right of the algorithm identifies the Certification Authority (CA). A blue arrow points downward from the algorithm and then left towards a certificate labeled "Bob's CA-signed certificate containing his public key, K (+/B)."