IBM z/OS SSL encryption options for the TN3270 Telnet Server must be specified properly.

During the SSL connection process a mutually acceptable encryption algorithm is selected by the server and client. This algorithm is used to encrypt the data that subsequently flows between the two. However, the level or strength of encryption can vary greatly. Certain configuration options can allow no encryption to be used and others can allow a relatively weak 40-bit algorithm to be used. Failure to properly enforce adequate encryption strength could result in the loss of data privacy.

Satisfies: SRG-OS-000033-GPOS-00014, SRG-OS-000120-GPOS-00061, SRG-OS-000250-GPOS-00093, SRG-OS-000393-GPOS-00173, SRG-OS-000394-GPOS-00174, SRG-OS-000396-GPOS-00176, SRG-OS-000478-GPOS-00223, SRG-OS-000423-GPOS-00187, SRG-OS-000424-GPOS-00188, SRG-OS-000425-GPOS-00189, SRG-OS-000426-GPOS-00190, SRG-OS-000478-GPOS-00223

From the ISPF Command Shell, enter: OMVS Enter: pasearch -t to display all Application Transparent Transport Layer Security (AT-TLS) policy entries.

If the TTLS cipher suites entries do not contain the following cipher suites, this is a finding.

Note: FIPS 140-3 minimum encryption is the accepted level of encryption and will override this requirement if greater.

Cipher Specifications

The following suites are allowed for the TLS 1.3 protocol: TLS_AES_128_GCM_SHA256 TLS_AES_256_GCM_SHA384

The following suites are allowed for the TLS 1.2 protocol: TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384 TLS_ECDH_RSA_WITH_AES_256_GCM_SHA384 TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256 TLS_ECDH_RSA_WITH_AES_128_GCM_SHA256

Configure AT-TLS policy to define security parameters. The policy must include the FIPS 140-3 cipher suites specified below.

Cipher Specifications

The following suites are allowed for the TLS 1.3 protocol: TLS_AES_128_GCM_SHA256 TLS_AES_256_GCM_SHA384

The following suites are allowed for the TLS 1.2 protocol: TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384 TLS_ECDH_RSA_WITH_AES_256_GCM_SHA384 TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256 TLS_ECDH_RSA_WITH_AES_128_GCM_SHA256

Note: Always check for the minimum allowed in FIPS 140-3.