SSL/TLS versions and cipher suites

An SSL cipher is an algorithm that performs encryption and decryption. It transforms plain text into a coded set of data (cipher text) that is not reversible without a key. During the SSL handshake phase of the connection, the client sends a list of the ciphers it supports. FortiADC examines the client cipher list in the order it is specified, chooses the first cipher that matches a cipher specified in the virtual server configuration, and responds to the client. If none of the ciphers offered by the client are in the cipher suite list for the virtual server, the SSL handshake fails.

To see the list of ciphers supported by the browser you are using, go to a link maintained by the Leibniz University of Hannover Distributed Computing & Security (DCSec) Research Group:

https://cc.dcsec.uni-hannover.de/

FortiADC SLB profiles support a specific list of RSA ciphers, PFS ciphers, ECDHE ciphers, ECDSA ciphers, and eNull ciphers.

Cipher suites with RSA key exchange lists supported RSA ciphers.

Cipher suites with RSA key exchange

Abbreviation	Cipher Suite	Protocol	Kx	Au	Enc	MAC
AES256-GCM-SHA384	TLS_RSA_WITH_AES_256_GCM_SHA384	TLS 1.2	RSA	RSA	AESGCM(256)	AEAD
AES256-SHA256	TLS_RSA_WITH_AES_256_CBC_SHA256	TLS 1.2	RSA	RSA	AES(256)	SHA
AES256-SHA	TLS_RSA_WITH_AES_256_CBC_SHA	SSL 3.0 TLS 1.2, 1.1, 1.0	RSA	RSA	AES(256)	SHA
AES128-GCM-SHA256	TLS_RSA_WITH_AES_128_GCM_SHA256	TLS 1.2	RSA	RSA	AESGCM(128)	AEAD
AES128-SHA256	TLS_RSA_WITH_AES_128_CBC_SHA256	TLS 1.2	RSA	RSA	AES(128)	SHA
AES128-SHA	TLS_RSA_WITH_AES_128_CBC_SHA	SSL 3.0 TLS 1.2, 1.1, 1.0	RSA	RSA	AES(128)	SHA
RC4-SHA	SSL_RSA_WITH_RC4_128_SHA	SSL 3.0	RSA	RSA	RC4	SHA
	TLS_RSA_WITH_RC4_128_SHA	TLS 1.2, 1.1, 1.0	RSA	RSA	RC4	SHA
RC4-MD5	SSL_RSA_WITH_RC4_128_MD5	SSL 3.0	RSA	RSA	RC4	MD5
	TLS_RSA_WITH_RC4_128_MD5	TLS 1.2, 1.1, 1.0	RSA	RSA	RC4	MD5
DES-CBC3-SHA	SSL_RSA_WITH_3DES_EDE_CBC_SHA	SSL 3.0	RSA	RSA	DES-CBC3	SHA
	TLS_RSA_WITH_3DES_EDE_CBC_SHA	TLS 1.2, 1.1, 1.0	RSA	RSA	DES-CBC3	SHA

With RSA ciphers, the server's public RSA key is part of the server certificate and is typically very long lived. It is not uncommon for the same public key to be used for months or years. This creates a potential problem: if an SSL server's private key were to be leaked or stolen, all connections made in the past using that key would be vulnerable. If someone has recorded your SSL connections, they can use the stolen private key to decrypt them.

Cipher suites with DHE/EDH key exchange lists supported Perfect Forward Secrecy (PFS) ciphers with DHE/EDH key exchange. With PFS, a fresh public key is created for every single connection.That means that an adversary would need to break the key for each connection individually to read the communication.

Cipher suites with DHE/EDH key exchange

Abbreviation	Cipher Suite	Protocol	Kx	Au	Enc	MAC
DHE-RSA-AES256-GCM-SHA384	TLS_DHE_RSA_WITH_AES_256_GCM_SHA384	TLS 1.2	DH	RSA	AES256	SHA384
DHE-RSA-AES256-SHA256	TLS_DHE_RSA_WITH_AES_256_CBC_SHA256	TLS 1.2	DH	RSA	AES256	SHA256
DHE-RSA-AES256-SHA	TLS_DHE_RSA_WITH_AES_256_CBC_SHA	SSL 3.0 TLS 1.2, 1.1, 1.0	DH	RSA	AES256	SHA256
DHE-RSA-AES128-GCM-SHA256	TLS_DHE_RSA_WITH_AES_128_GCM_SHA256	TLS 1.2	DH	RSA	AES128	SHA256
DHE-RSA-AES128-SHA256	TLS_DHE_RSA_WITH_AES_128_CBC_SHA256	TLS 1.2	DH	RSA	AES128	SHA256
DHE-RSA-AES128-SHA	TLS_DHE_RSA_WITH_AES_128_CBC_SHA	SSL 3.0 TLS 1.2, 1.1, 1.0	DH	RSA	AES128	SHA
EDH-RSA-DES-CBC3-SHA	TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA	SSL 3.0 TLS 1.2, 1.1, 1.0	DH	RSA	3DES	SHA

Cipher suites with EDCHE key exchange lists supported PFS ciphers with Elliptic curve Diffie–Hellman Ephemeral key (ECDHE) key exchange. ECDHE is significantly faster than DHE. The supported suites include both the Elliptic Curve Digital Signature Algorithm (ECDSA) and RSA key authentication (Au) algorithms.

Cipher suites with EDCHE key exchange

Abbreviation	Cipher Suite	Protocol	Kx	Au	Enc	MAC
ECDHE-ECDSA-AES256-GCM-SHA384	TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384	TLS 1.2	ECDH	ECDSA	AESGCM256	AEAD
ECDHE-ECDSA-AES256-SHA384	TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384	TLSv1.2	ECDH	ECDSA	AES256	SHA384
ECDHE-ECDSA-AES256-SHA	TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA	SSL 3.0 TLS 1.2, 1.1, 1.0	ECDH	ECDSA	AES256	SHA
ECDHE-ECDSA-AES128-GCM-SHA256	TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256	TLSv1.2	ECDH	ECDSA	AESGCM128	AEAD
ECDHE-ECDSA-AES128-SHA256	TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256	TLSv1.2	ECDH	ECDSA	AES128	SHA256
ECDHE-ECDSA-AES128-SHA	TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA	SSL 3.0 TLS 1.2, 1.1, 1.0	ECDH	ECDSA	AES128	SHA
ECDHE-ECDSA-RC4-SHA	TLS_ECDHE_ECDSA_WITH_RC4_128_SHA	SSL 3.0 TLS 1.2, 1.1, 1.0	ECDH	ECDSA	RC4	SHA
ECDHE-ECDSA-DES-CBC3-SHA	TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA	SSL 3.0 TLS 1.2, 1.1, 1.0	ECDH	ECDSA	3DES	SHA
ECDHE-RSA-AES256-GCM-SHA384	TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384	TLS 1.2	ECDH	RSA	AESGCM256	AEAD
ECDHE-RSA-AES256-SHA384	TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384	TLS 1.2	ECDH	RSA	AES256	SHA384
ECDHE-RSA-AES256-SHA	TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA	TLS 1.2	ECDH	RSA	AES256	SHA
ECDHE-RSA-AES128-GCM-SHA256	TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256	TLS 1.2	ECDH	RSA	AESGCM128	AEAD
ECDHE-RSA-AES128-SHA256	TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256	TLS 1.2	ECDH	RSA	AES128	SHA256
ECDHE-RSA-AES128-SHA	TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA	SSL 3.0	ECDH	RSA	AES128	SHA
ECDHE-RSA-RC4-SHA	TLS_ECDHE_RSA_WITH_RC4_128_SHA	SSL 3.0	ECDH	RSA	RC4	SHA
ECDHE-RSA-DES-CBC3-SHA	TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA	SSL 3.0	ECDH	RSA	3DES	SHA

Profiles support TLS_AES_128_GCM_SHA256 and TLS_AES_256_GCM_SHA384 for TLSv1.3. They will be set automatically when TLSv1.3 is selected in ssl version.

In addition, profiles support an eNull cipher option. This option represents all cipher suites that do not apply encryption to the application data (integrity check is still applied). The exact cipher suite used depends on the SSL/TLS version used. As an example, in SSL v3.0, eNULL includes NULL-MD5, NULL-SHA, ECDH-RSA-NULL-SHA, ECDH-ECDSA-NULL-SHA, and some other non-encryption cipher suites.

Finally, profiles support a user-specified cipher list. You can specify a colon-separated list of OpenSSL cipher suite short names. The names are validated against the form of the cipher suite short names published on the OpenSSL website:

https://www.openssl.org/docs/manmaster/apps/ciphers.html