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

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

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 system without being authorized

Security using Encryption Operation All secure 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.

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.

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

Receiver Functions: Digital Signature message { } Receive Decrypt session key with Receiver’s Private Key 1 Decrypt Bundle with Session Key 2 Digital Signature message Bundle 3 Public Key Decrypt MD with Sender’s Message Digest Create Message Digest 4 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