In this illustration, we once again see Alice and Bob, though this time without Trudy. Alice's computer is labeled "Encryption algorithm" and Bob's is labeled "Decryption algorithm." A blue arrow labeled "Plaintext message, m" extends from the left side of the figure and points to the encryption algorithm. A gray arrow extends from a key at the top of the figure, labeled "K (+/B) Public encryption key," and points to the encryption algorithm. A blue line, labeled "Ciphertext + K (+/B) (m)," extends from the encryption algorithm to the decryption algorithm. A blue arrow extends from a second key at the top of the figure, labeled "K (-/B) Private decryption key," to the decryption algorithm. A blue arrow labeled "m = K (-/B) (K (+/B) (m)))" extends from the decryption algorithm to the right, and then points upwards to a point labeled "Plaintext message, m."