1. E-mail Security using Encryption Security Features Message Origin Authentication - verifying that the sender is who he or she says they are Content Integrity - verifying that the message was not changed after sender sent it Content Confidentiality - making certain that only the intended recipient reads the message Proof of Delivery - making certain that the message was delivered Continued... 1 2 3 4

2. E-mail Security using Encryption Security Features Message Sequence Integrity - making certain that all messages were delivered in proper order. Non-repudiation of Origin - being able to prove that sender sent a message. Non-repudiation of Delivery - being able to prove that a recipient got a message. Continued... 5 6 7

3. E-mail Security using Encryption Security Features Message Security Labeling - labeling a message with handling instructions. Message Flow Confidentiality - making certain no one knows who you exchange mail with. Secure Access Management - making certain no one uses your e-mail system without being authorized. 8 9 10

4. E-mail Security using Encryption Operation All secure e-mail systems work roughly the same way. –Calculate a message digest of the message. –Encrypt the message digest with sender’s private key. –Encrypt the mail with a session key (random). –Encrypt the session key with receiver’s public key.

5. E-mail Security using Encryption Operation Receiver must: –Decrypt session key with the receiver’s private key. –Decrypt the message with session key. –Decrypt message digest with the sender’s public key. –Calculate a message digest and compare to the one that was sent. Encrypted message digest serves as both signature and integrity check.

6. Sender Functions: Email message Create Message Digest Private Key Encrypt MD with Sender’s Digital Signature Email message Encrypt Bundle with Session Key (Random Number) Digital Signature Email message Encrypt with Receiver’s Public Key { SEND } 1 2 Bundle 3 4 5 6 7 1 2 3 4 Set Reply Request 6 5 SN 8 9 10 Confidential Encapsulate Header Require Private Key to unlock Workstation SN Confidential SN Confidential Message Sequence No Security Labeling BUSINESS PROTOCOL

7. Receiver Functions: Digital Signature Email message { } Receive Decrypt session key with Receiver’s Private Key 1 Decrypt Bundle with Session Key 2 Digital Signature Email message Bundle 3 Public Key Decrypt MD with Sender’s Message Digest Create Message Digest 4 Email message SN Confidential SN Confidential 0 = { 5 6 Read Message Compare MD’s SN Confidential 7 Repeat Process in other direction for Non-Repudiation of Delivery BUSINESS PROTOCOL