DICOM PS3.15 2018b - Security and System Management Profiles

B.10 Non-Downgrading BCP195 TLS Secure Transport Connection Profile
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## B.10 Non-Downgrading BCP195 TLS Secure Transport Connection Profile

An implementation that supports the Non-Downgrading BCP195 TLS Profile shall utilize the framework and negotiation mechanism specified by the Transport Layer Security protocol. It shall comply with BCP195 from the IETF with the additional restrictions enumerated below.

The following additions are made to BCP195 requirements. They change some of the "should" recommendations in the RFC into requirements.

- Implementations shall not negotiate TLS version 1.1 [RFC4346] or TLS version 1.0 [RFC2246]

- Implementations shall not negotiate DTLS version 1.0 [RFC4347]

- In cases where an application protocol allows implementations or deployments a choice between strict TLS configuration and dynamic upgrade from unencrypted to TLS-protected traffic (such as STARTTLS), clients and servers shall prefer strict TLS configuration.

- Application protocols typically provide a way for the server to offer TLS during an initial protocol exchange, and sometimes also provide a way for the server to advertise support for TLS (e.g., through a flag indicating that TLS is required); unfortunately, these indications are sent before the communication channel is encrypted. A client shall attempt to negotiate TLS even if these indications are not communicated by the server.

- The following cipher suites shall all be supported:

  - TLS_DHE_RSA_WITH_AES_128_GCM_SHA256

  - TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256

  - TLS_DHE_RSA_WITH_AES_256_GCM_SHA384

  - TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384

- Additional cipher suites of similar or greater cryptographic strength may be supported.

TCP ports on which an implementation accepts TLS connections, or the mechanism by which these port numbers are selected or configured, shall be stated in the Conformance Statement. The TCP ports on which an implementation accepts TLS connections for DICOMWeb shall be different from those on which an implementation accepts TLS connections for DIMSE. The HTTP/HTTPS connection for DICOMWeb can be shared with other HTTP/HTTPS traffic.

The Conformance Statement shall also indicate what mechanisms the implementation supports for Key Management.

### Note

It is recommended that systems supporting the Non-Downgrading BCP195 TLS Profile use the registered port number "2762 dicom-tls" for the DICOM Upper Layer Protocol on TLS. If both the Non-Downgrading BCP195 TLS Profile and the BCP195 TLS Profile are supported, it is recommended that they use the well known port numbers on different IP addresses.

The Conformance Statement shall indicate what mechanisms the implementation supports for Key Management.

When an integrity check fails, the connection shall be dropped per the TLS protocol, causing both the sender and the receiver to issue an A-P-ABORT indication to the upper layers with an implementation-specific provider reason. The provider reason used shall be documented in the Conformance Statement.

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DICOM PS3.15 2018b - Security and System Management Profiles