斗 长 Public-Key Cryptography ￥斗 ★★ o All users pick a public key/private key pair publish the publickey private keynot published o Public key is the encryption key private key is the decryption key
21 Public-Key Cryptography All users pick a public key/private key pair – publish the public key – private key not published Public key is the encryption key – private key is the decryption key
斗 长 Public-key Encryption ￥斗 ★★ o Encryption/decryption process: crypt (clear text, e-key)= cipher-text-1 crypt(cipher-text-l, d-key)=cleartext crypt (cleartext, d-key)=cipher-text-2 crypt(cipher-text-2, e-key)=cleartext o In general d-key(e-key(msg))=e-key(d-key(msg)) But not al ways!
22 Public-key Encryption Encryption/decryption process: – crypt (clear text, e-key) = cipher-text-1 – crypt (cipher-text-1, d-key) = clear text – crypt (clear text, d-key) = cipher-text-2 – crypt (cipher-text-2, e-key) = clear text In general d-key(e-key(msg))=e-key(d-key(msg)) – But not always!
斗 长 Public-key Encryption ￥斗 ★★ s Note that cipher-text-1! cipher-text-2 crypt(cipher-text-2, d-key)!= cleartext crypt(cipher-text-1, e-key)!= cleartext o e-keyis called the public key Everyone knows the value of everyone's public keys
23 Public-key Encryption Note that – cipher-text-1 != cipher-text-2 – crypt(cipher-text-2, d-key) != clear text – crypt(cipher-text-1, e-key) != clear text e-key is called the “public key” – Everyone knows the value of everyone’s public keys
斗 长 Public-key Encryption ￥斗 ★★ o d-key is called the private key' Only the sender knows his/herown private key o Difficultto guess private key Even if you know the publickey and crypto. and lots of encrypted pairs
24 Public-key Encryption d-key is called the “private key” – Only the sender knows his/her own private key Difficult to guess private key – Even if you know the public key and crypt(), – and lots of encrypted pairs
斗 长 Public-key Encryption ￥斗 ★★ o Public-keyencryption can be used for authentication o For example: to authenticate sender zou, we do “ from zou” crypt( message,zou- private) o Anyone can read this message (no confidentiality) o Only zou can generate this message others can verify that zou generated the message by decrypting with zou-public
25 Public-key Encryption Public-key encryption can be used for authentication For example: to authenticate sender “zou”, we do: – “from zou” crypt (message, zou-private) Anyone can read this message (no confidentiality) Only zou can generate this message – Others can verify that zou generated the message – by decrypting with zou-public