Internet-Draft ACVP KDF TLS v1.3 November 2024
Hammett Expires 5 May 2025 [Page]
Workgroup:
Network Working Group
Internet-Draft:
:
Published:
Intended Status:
Informational
Expires:
Author:
R. Hammett, Ed.

ACVP TLS Key Derivation Function JSON Specification

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on 5 May 2025.

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Table of Contents

1. Acknowledgements

There are no acknowledgements.

2. Abstract

This document defines the JSON schema for testing RFC8446 TLS v1.3 KDF implementations with the ACVP specification.

3. Introduction

The Automated Crypto Validation Protocol (ACVP) defines a mechanism to automatically verify the cryptographic implementation of a software or hardware crypto module. The ACVP specification defines how a crypto module communicates with an ACVP server, including crypto capabilities negotiation, session management, authentication, vector processing and more. The ACVP specification does not define algorithm specific JSON constructs for performing the crypto validation. A series of ACVP sub-specifications define the constructs for testing individual crypto algorithms. Each sub-specification addresses a specific class of crypto algorithms. This sub-specification defines the JSON constructs for testing RFC8446 TLS v1.3 KDF implementations using ACVP.

4. Conventions

4.1. Notation conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 of [RFC2119] and [RFC8174] when, and only when, they appear in all capitals, as shown here.

4.2. Terms and Definitions

4.2.1. Prompt

JSON sent from the server to the client describing the tests the client performs

4.2.2. Registration

The initial request from the client to the server describing the capabilities of one or several algorithm, mode and revision combinations

4.2.3. Response

JSON sent from the client to the server in response to the prompt

4.2.4. Test Case

An individual unit of work within a prompt or response

4.2.5. Test Group

A collection of test cases that share similar properties within a prompt or response

4.2.6. Test Vector Set

A collection of test groups under a specific algorithm, mode, and revision

4.2.7. Validation

JSON sent from the server to the client that specifies the correctness of the response

5. Supported KDFs

The following key derivation functions MAY be advertised by the ACVP compliant cryptographic module:

6. Test Types and Test Coverage

This section describes the design of the tests used to validate RFC8446 TLS v1.3 KDF implementations.

6.1. Test Types

There is only one test type: functional tests. Each has a specific value to be used in the testType field. The testType field definition is:

  • "AFT" - Algorithm Functional Test. These tests can be processed by the client using a normal 'derive_key' operation. AFTs cause the implementation under test to exercise normal operations on a single block, multiple blocks, or partial blocks. In all cases, random data is used. The functional tests are designed to verify that the logical components of the key deriviation process are operating correctly.

6.2. Test Coverage

The tests described in this document have the intention of ensuring an implementation is conformant to [RFC8446].

6.2.1. Requirements Covered

  • RFC8446 - 7.1 Key Schedule. This section of the document encapsulates the bulk of ACVP testing; any functions involved in the computation of the TLS v1.3 KDF SHALL BE tested as a part of the vector set. Note that message construction that is defined by the protocol for messages such as ClientHello, ServerHello, etc SHALL NOT be within the scope of ACVP testing.
  • RFC8446 - 4.4.1 The Transcript Hash. The transcript hash is used within section 7.1 for deriving keying material and as such SHALL BE tested as a part of ACVP testing.

6.2.2. Requirements Not Covered

  • RFC8446 - ACVP testing for the TLS v1.3 KDF is done to ensure proper implementation of the KDF portion of the RFC; as such TLS protocol specific pieces are not tested. Protocol specific construction of messages such as the ClientHello, ServerHello, etc SHALL NOT be within the scope of ACVP testing.

7. Capabilities Registration

ACVP requires crypto modules to register their capabilities. This allows the crypto module to advertise support for specific algorithms, notifying the ACVP server which algorithms need test vectors generated for the validation process. This section describes the constructs for advertising support of TLS v1.3 KDF algorithms to the ACVP server.

The algorithm capabilities MUST be advertised as JSON objects within the 'algorithms' value of the ACVP registration message. The 'algorithms' value is an array, where each array element is an individual JSON object defined in this section. The 'algorithms' value is part of the 'capability_exchange' element of the ACVP JSON registration message. See the ACVP specification [ACVP] for more details on the registration message.

7.1. Prerequisites

Each algorithm implementation MAY rely on other cryptographic primitives. For example, RSA Signature algorithms depend on an underlying hash function. Each of these underlying algorithm primitives must be validated, either separately or as part of the same submission. ACVP provides a mechanism for specifying the required prerequisites:

Prerequisites, if applicable, MUST be submitted in the registration as the prereqVals JSON property array inside each element of the algorithms array. Each element in the prereqVals array MUST contain the following properties

Table 1: Prerequisite Properties
JSON Property Description JSON Type
algorithm a prerequisite algorithm string
valValue algorithm validation number string

A "valValue" of "same" SHALL be used to indicate that the prerequisite is being met by a different algorithm in the capability exchange in the same registration.

An example description of prerequisites within a single algorithm capability exchange looks like this

"prereqVals":
[
  {
    "algorithm": "Alg1",
    "valValue": "Val-1234"
  },
  {
    "algorithm": "Alg2",
    "valValue": "same"
  }
]

7.3. Registration Example

A registration SHALL use these properties

Table 2: TLS Registration JSON Values
JSON Property Description JSON Type Valid Values
algorithm Name of the algorithm to be validated string "TLS-v1.3"
mode Mode of the algorithm to be validated string "KDF"
revision ACVP Test version string "RFC8446"
hmacAlg HMAC functions supported array See Section 7.3.1
runningMode The supported key exchange modes for the KDF https://tools.ietf.org/html/rfc8446#section-2 array See Section 7.3.2

7.3.1. Valid HMAC Functions

The following hash functions MAY be advertised by an ACVP compliant client under the 'hmacAlg' property

  • SHA2-256
  • SHA2-384

7.3.2. Valid Running Modes

The KDF modes MAY be advertised by an ACVP compliant client under the 'runningMode' property

An example registration within an algorithm capability exchange looks like this

{
  "algorithm": "TLS-v1.3",
  "mode": "KDF",
  "revision": "RFC8446",
  "hmacAlg": [
    "SHA2-256",
    "SHA2-384",
    ],
  "runningMode": [
    "PSK-DHE"
  ]
}

8. Test Vectors

The ACVP server provides test vectors to the ACVP client, which are then processed and returned to the ACVP server for validation. A typical ACVP validation test session would require multiple test vector sets to be downloaded and processed by the ACVP client. Each test vector set represents an individual cryptographic algorithm defined during the capability exchange. This section describes the JSON schema for a test vector set used with RFC8446 TLS v1.3 KDF algorithms.

The test vector set JSON schema is a multi-level hierarchy that contains meta data for the entire vector set as well as individual test vectors to be processed by the ACVP client. The following table describes the JSON elements at the top level of the hierarchy.

Table 3: Top Level Test Vector JSON Elements
JSON Values Description JSON Type
acvVersion Protocol version identifier string
vsId Unique numeric vector set identifier integer
algorithm Algorithm defined in the capability exchange string
mode Mode defined in the capability exchange string
revision Protocol test revision selected string
testGroups Array of test group JSON objects, which are defined in Section 8.1 array

An example of this would look like this

[
  {
    "acvVersion": <version>
  },
  {
    "vsId": 1,
    "algorithm": "Alg1",
    "mode": "Mode1",
    "revision": "Revision1.0",
    "testGroups": [ ... ]
  }
]

8.1. Test Groups

The testGroups element at the top level in the test vector JSON object is an array of test groups. Test vectors are grouped into similar test cases to reduce the amount of data transmitted in the vector set. For instance, all test vectors that use the same key size would be grouped together. The Test Group JSON object contains meta data that applies to all test vectors within the group. The following table describes the RFC8446 TLS v1.3 KDF JSON elements of the Test Group JSON object

Table 4: Test Group JSON Object
JSON Value Description JSON Type
tgId Test group identifier integer
testType Test operations to be performed string
hmacAlg SHA version used string
runningMode The key exchange mode used string
tests Array of individual test cases array

The 'tgId', 'testType' and 'tests' objects MUST appear in every test group element communicated from the server to the client as a part of a prompt. Other properties are dependent on which 'testType' (see Section 6) the group is addressing.

8.2. Test Cases

Each test group contains an array of one or more test cases. Each test case is a JSON object that represents a single test vector to be processed by the ACVP client. The following table describes the JSON elements for each RFC8446 TLS v1.3 KDF test vector.

Table 5: Test Case JSON Object
JSON Value Description JSON Type
tcId Test case identifier integer
psk Random pre-shared key, included for PSK and PSK-DHE running modes. hex
dhe Random Diffie-Hellman shared secret, included for DHE and PSK-DHE running modes. hex
helloClientRandom Randomly generated Client Hello message hex
helloServerRandom Randomly generated Server Hello message hex
finishedClientRandom Randomly generated Client Finished message hex
finishedServerRandom Randomly generated Server Finished message hex

Note that when the PSK or DHE are not included in the test case, it is assumed they are the digest size of the group's hash set to zero. As an example, for a test group using SHA2-256, with a running mode of "DHE", the "PSK" would be represented by a BitString of 256 bits or 32 bytes, all being "0".

Here is an abbreviated yet fully constructed example of the prompt.

{
    "vsId": 1,
    "algorithm": "TLS-v1.3",
    "mode": "KDF",
    "revision": "RFC8446",
    "testGroups": [
        {
            "tgId": 1,
            "testType": "AFT",
            "hmacAlg": "SHA2-256",
            "runningMode": "PSK-DHE",
            "tests": [{
                "tcId": 1,
                "psk": "C2A39E5D172C7D147B5FD3752E4C0840EDDF7C5684B00E7B1AA20B7F56CF64F1EE05",
                "dhe": "EE6ADDBC8BDF014254051D78D7A0ECE35AAB230024647E871B375C257E23FC814235",
                "helloClientRandom": "7613AA5EAC7D233CCFF764C95D22B6BB026C087DF017E04C5AF6F0E2C1C9E3FA134F",
                "helloServerRandom": "A1CDA1FC4A72BF85FAEC964AF1CBB421BA1FD683513C24D11EE0B0092190C729ECD4",
                "finishedClientRandom": "F77C6488E63463FEDACA4CEF38F66E1957BDCB1F9A6719029F75590687487AF7F235",
                "finishedServerRandom": "9B562F22963D4A9C96DA93A1E3AA5F88A48CA7A0EA92D293AA7C72AD9A71A4DF911B"
            }]
        }
    ]
}

9. Responses

After the ACVP client downloads and processes a vector set, it must send the response vectors back to the ACVP server. The following table describes the JSON object that represents a vector set response.

Table 6: Vector Set Response JSON Object
JSON Property Description JSON Type
acvVersion The version of the protocol string
vsId The vector set identifier integer
testGroups The test group data array

An example of this is the following

{
    "acvVersion": "version",
    "vsId": 1,
    "testGroups": [ ... ]
}

The testGroups section is used to organize the ACVP client response in a similar manner to how it receives vectors. Several algorithms SHALL require the client to send back group level properties in their response. This structure helps accommodate that.

Table 7: Vector Set Group Response JSON Object
JSON Property Description JSON Type
tgId The test group identifier integer
tests The test case data array

An example of this is the following

{
    "tgId": 1,
    "tests": [ ... ]
}

The following table describes the JSON object that represents a test case response for a RFC8446 TLS v1.3 KDF.

Table 8: Test Case Results JSON Object
JSON Property Description JSON Type
tcId The test case identifier integer
clientEarlyTrafficSecret The client early traffic secret. Derive-Secret(., "c e traffic", ClientHello) hex
earlyExporterMasterSecret The early exporter master secret. Derive-Secret(., "e exp master", ClientHello) hex
clientHandshakeTrafficSecret The client handshake traffic secret. Derive-Secret(., "c hs traffic", ClientHello...ServerHello) hex
serverHandshakeTrafficSecret The server handshake traffic secret. Derive-Secret(., "s hs traffic", ClientHello...ServerHello) hex
clientApplicationTrafficSecret The client application traffic secret. Derive-Secret(., "c ap traffic", ClientHello...server Finished) hex
serverApplicationTrafficSecret The server application traffic secret. Derive-Secret(., "s ap traffic", ClientHello...server Finished) hex
exporterMasterSecret The exporter master secret. Derive-Secret(., "exp master", ClientHello...server Finished) hex
resumptionMasterSecret The resumption master secret. Derive-Secret(., "res master", ClientHello...client Finished) hex

Here is an abbreviated example of the response

{
  "vsId": 1,
  "testGroups": [{
    "tgId": 1,
    "tests": [{
      "tcId": 1,
      "clientEarlyTrafficSecret": "6C4A2365493D1AF0F654D59A181EDD2510205F6AE3F22B6EE765B8208C99C66C",
      "earlyExporterMasterSecret": "3C7204D21F2C10CD744915221CD46B8CF914E5E3124C87A822959C4EB58F13B9",
      "clientHandshakeTrafficSecret": "C017D71DB97422E10BF950C1B530AB754A11D4FCF562DDBB47EE6DBAAD72CBA3",
      "serverHandshakeTrafficSecret": "42D17CF61E98CA182AF677E13D40EA513627D950156BC8D80E749AB789930DE7",
      "clientApplicationTrafficSecret": "52E4E879CA4AA2314AE5F2CCF3870BA879AE2644DB96BEC71493ADEAEE8EA121",
      "serverApplicationTrafficSecret": "D4D3C87A5B5F165E90807BA7954734BA733668E9858CCE3F34B1A3E4965681F8",
      "exporterMasterSecret": "7880C0A3BC51A1B2FE4013DB481B17B3D0A1DC6C3688EB178BF6FCD3D306AE9A",
      "resumptionMasterSecret": "753DB3A1743DAA17AE52E2B6AA6E00AA07DA46111A43653325C98D69079E7BF4"
    }]
  }]
}

10. Security Considerations

There are no additional security considerations outside of those outlined in the ACVP document.

11. IANA Considerations

This document does not require any action by IANA.

12. References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", RFC 8174, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446]
Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, RFC 8446, DOI 10.17487/RFC8446, , <https://www.rfc-editor.org/info/rfc8446>.
[ACVP]
Fussell, B., Vassilev, A., Booth, H., Celi, C., and R. Hammett, "Automatic Cryptographic Validation Protocol", .

Author's Address

Russ Hammett (editor)