Electronic Mail Security-System Security and Cryptography-Lecture Slides, Slides of Cryptography and System Security

Download Electronic Mail Security-System Security and Cryptography-Lecture Slides and more Slides Cryptography and System Security in PDF only on Docsity! Chapter 15 – Electronic Mail Security Despite the refusal of VADM Poindexter and LtCol North to appear, the Board's access to other sources of information filled much of this gap. The FBI provided documents taken from the files of the National Security Advisor and relevant NSC staff members, including messages from the PROF system between VADM Poindexter and LtCol North. The PROF messages were conversations by computer, written at the time events occurred and presumed by the writers to be protected from disclosure. In this sense, they provide a first-hand, contemporaneous account of events. —The Tower Commission Report to President Reagan on the Iran-Contra Affair, 1987 docsity.com Email Security  email is one of the most widely used and regarded network services  currently message contents are not secure  may be inspected either in transit  or by suitably privileged users on destination system docsity.com PGP Operation – Authentication 1. sender creates message 2. use SHA-1 to generate 160-bit hash of message 3. signed hash with RSA using sender's private key, and is attached to message 4. receiver uses RSA with sender's public key to decrypt and recover hash code 5. receiver verifies received message using hash of it and compares with decrypted hash code docsity.com PGP Operation – Confidentiality 1. sender generates message and 128-bit random number as session key for it 2. encrypt message using CAST-128 / IDEA / 3DES in CBC mode with session key 3. session key encrypted using RSA with recipient's public key, & attached to msg 4. receiver uses RSA with private key to decrypt and recover session key 5. session key is used to decrypt message docsity.com PGP Operation – Confidentiality & Authentication  can use both services on same message  create signature & attach to message  encrypt both message & signature  attach RSA/ElGamal encrypted session key docsity.com PGP Operation — Summary {a) Generic Transmission Diagram (from A) (b) Generic Reception Diagram (to B) 3 docsity.com PGP Session Keys  need a session key for each message  of varying sizes: 56-bit DES, 128-bit CAST or IDEA, 168-bit Triple-DES  generated using ANSI X12.17 mode  uses random inputs taken from previous uses and from keystroke timing of user docsity.com PGP Public & Private Keys  since many public/private keys may be in use, need to identify which is actually used to encrypt session key in a message  could send full public-key with every message  but this is inefficient  rather use a key identifier based on key  is least significant 64-bits of the key  will very likely be unique  also use key ID in signatures docsity.com PGP Message Generation Public key ring pssphvase_——»(H ) iD select 8 ——> LI Private key ring Key ID select encrypted ID, > LI] U private key DC Key ID public key private key PU, PR, message digest # _— session key = Message} Output ed M signature message + message encrypted signature + message 3 docsity.com PGP Message Reception passphase___o(H ) Private key ring select encrypted U private key DC private key PR, receiver's Key ID. Encrypted session key encrypted| message + signature session key select Public key ring | © docsity.com PGP Key Management  rather than relying on certificate authorities  in PGP every user is own CA  can sign keys for users they know directly  forms a “web of trust”  trust keys have signed  can trust keys others have signed if have a chain of signatures to them  key ring includes trust indicators  users can also revoke their keys docsity.com S/MIME Cryptographic Algorithms  digital signatures: DSS & RSA  hash functions: SHA-1 & MD5  session key encryption: ElGamal & RSA message encryption: AES, Triple-DES, RC2/40 and others MAC: HMAC with SHA-1  have process to decide which algs to use docsity.com S/MIME Messages  S/MIME secures a MIME entity with a signature, encryption, or both  forming a MIME wrapped PKCS object  have a range of content-types:  enveloped data  signed data  clear-signed data  registration request  certificate only message docsity.com S/MIME Certificate Processing  S/MIME uses X.509 v3 certificates managed using a hybrid of a strict X.509 CA hierarchy & PGP’s web of trust  each client has a list of trusted CA’s certs  and own public/private key pairs & certs  certificates must be signed by trusted CA’s docsity.com