Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols are universally accepted standards for authenticated and encrypted communication between clients and servers. Both client and server authentication occur over SSL/TLS.
SSL3.0 is no longer supported due to security reasons. Using TLS 1.2 ciphers is strongly recommended if the environment allows it.
SSL/TLS uses a combination of public-key and symmetric-key encryption. Symmetric-key encryption is much faster than public-key encryption, but public-key encryption provides better authentication techniques. An SSL/TLS session always begins with an exchange of messages called handshake, initial communication between the server and client. The handshake allows the server to authenticate itself to the client using public-key techniques, optionally allows the client to authenticate to the server, then allows the client and the server to cooperate in the creation of symmetric keys used for rapid encryption, decryption, and integrity verification during the session that follows.
Both SSL and TLS support a variety of different cryptographic algorithms, or ciphers, for operations such as authenticating the server and client, transmitting certificates, and establishing session keys. Clients and servers may support different cipher suites, or sets of ciphers. Among other functions, the handshake determines how the server and client negotiate which cipher suite is used to authenticate each other, to transmit certificates, and to establish session keys.
Key-exchange algorithms like RSA and Elliptic Curve Diffie-Hellman (ECDH) govern the way the server and client determine the symmetric keys to use during an SSL/TLS session. The most common SSL cipher suites use RSA key exchange, while TLS supports ECC (Elliptic Curve Cryptography) cipher suites, as well as RSA. The Certificate System supports both RSA and ECC public-key cryptographic systems natively.
In more recent practise, key-exchange algorithms are being superseded by key-agreement protocols where each of the two or more parties can influence the outcome when establishing a common key for secure communication. Key agreement is preferrable to key exchange because it allows for Perfect Forward Secrecy (PFS) to be implemented. When PFS is used, random public keys (also called temporary cipher parameters or ephemeral keys) are generated for each session by a non-deterministic algorithm for the purposes of key agreement. As a result, there is no single secret value which could lead to the compromise of multiple messages, protecting past and future communication alike.
Longer RSA keys are required to provide security as computing capabilities increase. The recommended RSA key-length is 2048 bits. Though many servers continue to use 1024-bit keys, servers should migrate to at least 2048 bits. For 64-bit machines, consider using stronger keys. All CAs should use at least 2048-bit keys, and stronger keys (such as 3072 or 4096 bits) if possible.
3.2.1. Supported Cipher Suites
Cipher and hashing algorithms are in a constant flux with regard to various vulnerabilities and security strength. As a general rule, Red Hat Certificate System 9 follows the NIST guideline
and supports TLS 1.1 and TLS 1.2 cipher suites pertaining to the server keys.
Elliptic Curve Cryptography (ECC) is a cryptographic system that uses elliptic curves to create keys for encrypting data. ECC creates cryptographically-stronger keys with shorter key lengths than RSA, which makes it faster and more efficient to implement.
Certificate System supports ECC with the ECC with CA, KRA, and OCSP subsystems, so ECC certificate requests can be submitted to CAs through any of the enrollment profiles and ECC keys can be archived and restored in the KRA. Certificate System supports ECC natively; for more information, see Chapter 9, Installing an Instance with ECC System Certificates
Only the CA signing certificate is required; if for support purposes it is better to use RSA client certificates with the CA, simply delete the ECC subsystem certificates (except for the signing certificate) and replace them with RSA certificates..