18.5 Email Encryption

Digital Signature (?)

• Digital signature used asymmetric cryptography to simulate the security properties of a signature in digital, rather than written form.
• A digital signature may be further protected, by encrypting the signed email for confidentiality.

SSL (Secure Sockets Layer)

• SSL is an application layer protocol developed by Netscape for managing the security of a message transmission on the Internet.
• It uses RSA asymmetric (public key) encryption to encrypt data transferred over SSL connections.

Transport Layer Security (TLS)

• TLS is a protocol to establish a secure connection between a client and a server and ensure privacy and integrity of information during transmission.
• It uses the RSA algorithm with 1024 and 2048 bit strengths.
• TLS Handshake Protocol: It allows the client and server to authenticate each other, select encryption algorithm, and exchange symmetric key prior to data exchange.
• TLS Record Protocol: It provides secured connections with an encryption method such as Data Encryption Standard (DES).

It uses symmetric key for bulk encryption, asymmetric key for authentication and key exchange, and message authentication codes for message integrity.

Pretty Good Privacy (PGP) (重要)

• PGP (Pretty Good Privacy) is a protocol used to encrypt and decrypt data that provides authentication and cryptographic privacy.
• PGP is often used for data compression, digital signing, encryption and decryption of messages, emails, files, directories, and to enhance privacy of email communications.
• PGP combines the best features of both conventional and public key cryptography and is therefore known as hybrid cryptosystem.

PGP uses RSA(非對稱) for computing digital signatures and MD5 for computing message digests.