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# Standards Compliance

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## Purpose

This section describes the current state of standards compliance of the ssl application.

## Common (prior to TLS 1.3)

- For security reasons RSA key exchange cipher suites are no longer supported by default, but can be configured. (OTP 21)
- For security reasons DES cipher suites are no longer supported by default, but can be configured. (OTP 20)
- For security reasons 3DES cipher suites are no longer supported by default, but can be configured. (OTP 21)
- Renegotiation Indication Extension RFC 5746 is supported
- Ephemeral Diffie-Hellman cipher suites are supported, but not Diffie Hellman Certificates cipher suites.
- Elliptic Curve cipher suites are supported if the Crypto application supports it and named curves are used.
- Export cipher suites are not supported as the U.S. lifted its export restrictions in early 2000.
- IDEA cipher suites are not supported as they have become deprecated by the TLS 1.2 specification so it is not motivated to implement them.
- Compression is not supported.
- It is possible to use Pre-Shared Key (PSK) and Secure Remote Password (SRP) cipher suites, but they are not enabled by default and need addition configuration.

## Common

- CRL validation is supported.
- Policy certificate extensions are supported. (OTP 27)
- 'Server Name Indication' extension (RFC 6066) is supported.
- Application Layer Protocol Negotiation (ALPN) and its successor Next Protocol Negotiation (NPN) are supported.

## SSL 2.0

For security reasons SSL-2.0 is not supported. Interoperability with SSL-2.0 enabled clients dropped. (OTP 21)

## SSL 3.0

For security reasons SSL-3.0 is no longer supported at all. (OTP 23)

For security reasons SSL-3.0 is no longer supported by default, but can be configured. (OTP 19)

## TLS 1.0

For security reasons TLS-1.0 is no longer supported by default, but can be configured. (OTP 22)

## TLS 1.1

For security reasons TLS-1.1 is no longer supported by default, but can be configured. (OTP 22)

## TLS 1.2

Supported

## DTLS 1.0

For security reasons DTLS-1.0 (based on TLS 1.1) is no longer supported by default, but can be configured. (OTP 22)

## DTLS 1.2

Supported (based on TLS 1.2)

## DTLS 1.3

Not yet supported

## TLS 1.3

OTP-22 introduces support for TLS 1.3. The current implementation supports a selective set of cryptographic algorithms:

- Key Exchange: ECDHE groups supported by default
- Groups: all standard groups supported for the Diffie-Hellman key exchange
- Groups: Support brainpool groups from RFC 8734
- Ciphers: all mandatory cipher suites are supported
- Signature Algorithms: All algorithms form RFC 8446
- Certificates: RSA, ECDSA and EDDSA keys

Other notable features:

- PSK and session resumption is supported (stateful and stateless tickets)
- Anti-replay protection using Bloom-filters with stateless tickets
- Early data and 0-RTT is supported
- Key and Initialization Vector Update is supported

For more detailed information see the Standards Compliance below.

The following table describes the current state of standards compliance for TLS 1.3.

(C = Compliant, NC = Non-Compliant, PC = Partially-Compliant, NA = Not Applicable)

Section | Feature | State | Since
--- | --- | --- | ---
1.3. Updates Affecting TLS 1.2 |  | C | 24.1
| Version downgrade protection mechanism | C | 22
| RSASSA-PSS signature schemes | C | 24.1
| supported_versions (ClientHello) extension | C | 22
| signature_algorithms_cert extension | C | 24.1
2. Protocol Overview |  | PC | 22
| (EC)DHE | C | 22
| PSK-only | NC |
| PSK with (EC)DHE | C | 22.2
2.1. Incorrect DHE share | HelloRetryRequest | C | 22
2.2. Resumption and Pre-Shared Key (PSK) |  | C | 22.2
2.3. 0-RTT Data |  | PC | 23.3
4.1.1. Cryptographic Negotiation |  | C | 22.2
| supported_groups extension | C | 22
| signature_algorithms extension | C | 22
| pre_shared_key extension | C | 22.2
4.1.2. Client Hello | Client | PC | 22.1
| server_name (RFC6066) | C | 23.2
| max_fragment_length (RFC6066) | C | 23.0
| status_request (RFC6066) | C | 27.0
| supported_groups (RFC7919) | C | 22.1
| signature_algorithms (RFC8446) | C | 22.1
| use_srtp (RFC5764) | C | 26.0
| heartbeat (RFC6520) | NC |
| application_layer_protocol_negotiation (RFC7301) | C | 22.1
| signed_certificate_timestamp (RFC6962) | NC |
| client_certificate_type (RFC7250) | NC |
| server_certificate_type (RFC7250) | NC |
| padding (RFC7685) | NC |
| key_share (RFC8446) | C | 22.1
| pre_shared_key (RFC8446) | C | 22.2
| psk_key_exchange_modes (RFC8446) | C | 22.2
| early_data (RFC8446) | C | 23.3
| cookie (RFC8446) | C | 23.1
| supported_versions (RFC8446) | C | 22.1
| certificate_authorities (RFC8446) | C | 24.3
| oid_filters (RFC8446) | NC |
| post_handshake_auth (RFC8446) | NC |
| signature_algorithms_cert (RFC8446) | C | 22.1
| Server | PC | 22
| server_name (RFC6066) | C | 23.2
| max_fragment_length (RFC6066) | C | 23.0
| status_request (RFC6066) | NC |
| supported_groups (RFC7919) | C | 22
| signature_algorithms (RFC8446) | C | 22
| use_srtp (RFC5764) | C | 26.0
| heartbeat (RFC6520) | NC |
| application_layer_protocol_negotiation (RFC7301) | C | 22.1
| signed_certificate_timestamp (RFC6962) | NC |
| client_certificate_type (RFC7250) | NC |
| server_certificate_type (RFC7250) | NC |
| padding (RFC7685) | NC |
| key_share (RFC8446) | C | 22
| pre_shared_key (RFC8446) | C | 22.2
| psk_key_exchange_modes (RFC8446) | C | 22.2
| early_data (RFC8446) | C | 23.3
| cookie (RFC8446) | C | 23.1
| supported_versions (RFC8446) | C | 22
| oid_filters (RFC8446) | NC |
| post_handshake_auth (RFC8446) | NC |
| signature_algorithms_cert (RFC8446) | C | 22
4.1.3. Server Hello | Client | C | 22.2
| Version downgrade protection | C | 22.1
| key_share (RFC8446) | C | 22.1
| pre_shared_key (RFC8446) | C | 22.2
| supported_versions (RFC8446) | C | 22.1
| use_srtp (RFC5764) | C | 26.0
| Server | C | 22.2
| Version downgrade protection | C | 22
| key_share (RFC8446) | C | 22
| pre_shared_key (RFC8446) | C | 22.2
| supported_versions (RFC8446) | C | 22
| use_srtp (RFC5764) | C | 26.0
4.1.4. Hello Retry Request | Server | C | 22
| key_share (RFC8446) | C | 22
| cookie (RFC8446) | C | 23.1
| supported_versions (RFC8446) | C | 22
4.2.1. Supported Versions | Client | C | 22.1
| Server | C | 22
4.2.2. Cookie | Client | C | 23.1
| Server | C | 23.1
4.2.3. Signature Algorithms | Client | C | 24
| rsa_pkcs1_sha256 | C | 22.1
| rsa_pkcs1_sha384 | C | 22.1
| rsa_pkcs1_sha512 | C | 22.1
| ecdsa_secp256r1_sha256 | C | 22.1
| ecdsa_secp384r1_sha384 | C | 22.1
| ecdsa_secp521r1_sha512 | C | 22.1
| rsa_pss_rsae_sha256 | C | 22.1
| rsa_pss_rsae_sha384 | C | 22.1
| rsa_pss_rsae_sha512 | C | 22.1
| ed25519 | C | 24
| ed448 | C | 24
| rsa_pss_pss_sha256 | C | 23
| rsa_pss_pss_sha384 | C | 23
| rsa_pss_pss_sha512 | C | 23
| rsa_pkcs1_sha1 | C | 22.1
| ecdsa_sha1 | C | 22.1
| Server | C | 24
| rsa_pkcs1_sha256 | C | 22
| rsa_pkcs1_sha384 | C | 22
| rsa_pkcs1_sha512 | C | 22
| ecdsa_secp256r1_sha256 | C | 22.1
| ecdsa_secp384r1_sha384 | C | 22.1
| ecdsa_secp521r1_sha512 | C | 22.1
| rsa_pss_rsae_sha256 | C | 22
| rsa_pss_rsae_sha384 | C | 22
| rsa_pss_rsae_sha512 | C | 22
| ed25519 | C | 24
| ed448 | C | 24
| rsa_pss_pss_sha256 | C | 23
| rsa_pss_pss_sha384 | C | 23
| rsa_pss_pss_sha512 | C | 23
| rsa_pkcs1_sha1 | C | 22
| ecdsa_sha1 | C | 22
4.2.4. Certificate Authorities | Client | C | 24.3
| Server | C | 24.3
4.2.5. OID Filters | Client | NC |
| Server | NC |
4.2.6. Post-Handshake Client Authentication | Client | NC |
| Server | NC |
4.2.7. Supported Groups | Client | C | 22.1
| secp256r1 | C | 22.1
| secp384r1 | C | 22.1
| secp521r1 | C | 22.1
| x25519 | C | 22.1
| x448 | C | 22.1
| ffdhe2048 | C | 22.1
| ffdhe3072 | C | 22.1
| ffdhe4096 | C | 22.1
| ffdhe6144 | C | 22.1
| ffdhe8192 | C | 22.1
| Server | C | 22
| secp256r1 | C | 22
| secp384r1 | C | 22
| secp521r1 | C | 22
| x25519 | C | 22
| x448 | C | 22
| ffdhe2048 | C | 22
| ffdhe3072 | C | 22
| ffdhe4096 | C | 22
| ffdhe6144 | C | 22
| ffdhe8192 | C | 22
4.2.8. Key Share | Client | C | 22.1
| Server | C | 22
4.2.9. Pre-Shared Key Exchange Modes | Client | C | 22.2
| Server | C | 22.2
4.2.10. Early Data Indication | Client | C | 23.3
| Server | C | 23.3
4.2.11. Pre-Shared Key Extension | Client | C | 22.2
| Server | C | 22.2
4.2.11.1. Ticket Age | Client | C | 22.2
| Server | C | 22.2
4.2.11.2. PSK Binder | Client | C | 22.2
| Server | C | 22.2
4.2.11.3. Processing Order | Client | NC |
| Server | NC |
4.3.1. Encrypted Extensions | Client | PC | 22.1
| server_name (RFC6066) | C | 23.2
| max_fragment_length (RFC6066) | C | 23.0
| supported_groups (RFC7919) | NC |
| use_srtp (RFC5764) | NC |
| heartbeat (RFC6520) | NC |
| application_layer_protocol_negotiation (RFC7301) | C | 23.0
| client_certificate_type (RFC7250) | NC |
| server_certificate_type (RFC7250) | NC |
| early_data (RFC8446) | C | 23.3
| Server | PC | 22
| server_name (RFC6066) | C | 23.2
| max_fragment_length (RFC6066) | C | 23.0
| supported_groups (RFC7919) | NC |
| use_srtp (RFC5764) | NC |
| heartbeat (RFC6520) | NC |
| application_layer_protocol_negotiation (RFC7301) | C | 23.0
| client_certificate_type (RFC7250) | NC |
| server_certificate_type (RFC7250) | NC |
| early_data (RFC8446) | C | 23.3
4.3.2. Certificate Request | Client | PC | 22.1
| status_request (RFC6066) | NC |
| signature_algorithms (RFC8446) | C | 22.1
| signed_certificate_timestamp (RFC6962) | NC |
| certificate_authorities (RFC8446) | C | 24.3
| oid_filters (RFC8446) | NC |
| signature_algorithms_cert (RFC8446) | C | 22.1
| Server | PC | 22
| status_request (RFC6066) | NC |
| signature_algorithms (RFC8446) | C | 22
| signed_certificate_timestamp (RFC6962) | NC |
| certificate_authorities (RFC8446) | C | 24.3
| oid_filters (RFC8446) | NC |
| signature_algorithms_cert (RFC8446) | C | 22
4.4.1. The Transcript Hash |  | C | 22
4.4.2. Certificate | Client | PC | 22.1
| Arbitrary certificate chain orderings | C | 22.2
| Extraneous certificates in chain | C | 23.2
| status_request (RFC6066) | C | 27.0
| signed_certificate_timestamp (RFC6962) | NC |
| Server | PC | 22
| status_request (RFC6066) | NC |
| signed_certificate_timestamp (RFC6962) | NC |
4.4.2.1. OCSP Status and SCT Extensions | Client | PC | 27.0
| Server | NC |
4.4.2.2. Server Certificate Selection |  | C | 24.3
| The certificate type MUST be X.509v3, unless explicitly negotiated otherwise | C | 22
| The server's end-entity certificate's public key (and associated restrictions) MUST be compatible with the selected authentication algorithm from the client's "signature_algorithms" extension (currently RSA, ECDSA, or EdDSA). | C | 22
| The certificate MUST allow the key to be used for signing with a signature scheme indicated in the client's "signature_algorithms"/"signature_algorithms_cert" extensions | C | 22
| The "server_name" and "certificate_authorities" extensions are used to guide certificate selection. As servers MAY require the presence of the "server_name" extension, clients SHOULD send this extension, when applicable. | C | 24.3
4.4.2.3. Client Certificate Selection |  | PC | 22.1
| The certificate type MUST be X.509v3, unless explicitly negotiated otherwise | C | 22.1
| If the "certificate_authorities" extension in the CertificateRequest message was present, at least one of the certificates in the certificate chain SHOULD be issued by one of the listed CAs. | C | 24.3
| The certificates MUST be signed using an acceptable signature algorithm | C | 22.1
| If the CertificateRequest message contained a non-empty "oid_filters" extension, the end-entity certificate MUST match the extension OIDs that are recognized by the client | NC |
4.4.2.4. Receiving a Certificate Message | Client | C | 22.1
| Server | C | 22
4.4.3. Certificate Verify | Client | C | 22.1
| Server | C | 22
4.4.4. Finished | Client | C | 22.1
| Server | C | 22
4.5. End of Early Data | Client | C | 23.3
| Server | C | 23.3
4.6.1. New Session Ticket Message | Client | C | 23.3
| early_data (RFC8446) | C | 23.3
| Server | C | 23.3
| early_data (RFC8446) | C | 23.3
4.6.2. Post-Handshake Authentication | Client | NC |
| Server | NC |
4.6.3. Key and Initialization Vector Update | Client | C | 22.3
| Server | C | 22.3
5.1. Record Layer |  | C | 22
| MUST NOT be interleaved with other record types | C | 22
| MUST NOT span key changes | C | 22
| MUST NOT send zero-length fragments | C | 22
| Alert messages MUST NOT be fragmented | C | 22
5.2. Record Payload Protection |  | C | 22
5.3. Per-Record Nonce |  | C | 22
5.4. Record Padding |  | PC | 22
| MAY choose to pad | NC |
| MUST NOT send Handshake and Alert records that have a zero-length TLSInnerPlaintext.content | NC |
| The padding sent is automatically verified | C | 22
5.5. Limits on Key Usage |  | C | 22.3
6.1. Closure Alerts |  | 22 |

| close_notify | C | 22 |
| user_cancelled | C | 22 |

6.2. Error Alerts |  | PC | 22
7.1. Key Schedule |  | C | 22
7.2. Updating Traffic Secrets |  | C | 22
7.3. Traffic Key Calculation |  | C | 22
7.5. Exporters |  | PC | 26.3
8. 0-RTT and Anti-Replay |  | C | 22.2
8.1. Single-Use Tickets |  | C | 22.2
8.2. Client Hello Recording |  | C | 22.2
8.3. Freshness Checks |  | C | 22.2
9.1. Mandatory-to-Implement Cipher Suites |  | C | 22.1
| MUST implement the TLS_AES_128_GCM_SHA256 | C | 22
| SHOULD implement the TLS_AES_256_GCM_SHA384 | C | 22
| SHOULD implement the TLS_CHACHA20_POLY1305_SHA256 | C | 22
| Digital signatures | C | 22.1
| MUST support rsa_pkcs1_sha256 (for certificates) | C | 22
| MUST support rsa_pss_rsae_sha256 (for CertificateVerify and certificates) | C | 22
| MUST support ecdsa_secp256r1_sha256 | C | 22.1
| Key Exchange | C | 22
| MUST support key exchange with secp256r1 | C | 22
| SHOULD support key exchange with X25519 | C | 22
9.2. Mandatory-to-Implement Extensions |  | C | 23.2
| Supported Versions | C | 22
| Cookie | C | 23.1
| Signature Algorithms | C | 22
| Signature Algorithms Certificate | C | 22
| Negotiated Groups | C | 22
| Key Share | C | 22
| Server Name Indication | C | 23.2
| MUST send and use these extensions | C | 22.2
| "supported_versions" is REQUIRED for ClientHello, ServerHello and HelloRetryRequest | C | 22.1
| "signature_algorithms" is REQUIRED for certificate authentication | C | 22
| "supported_groups" is REQUIRED for ClientHello messages using (EC)DHE key exchange | C | 22
| "key_share" is REQUIRED for (EC)DHE key exchange | C | 22
| "pre_shared_key" is REQUIRED for PSK key agreement | C | 22.2
| "psk_key_exchange_modes" is REQUIRED for PSK key agreement | C | 22.2
| TLS 1.3 ClientHello | C | 22.1
| If not containing a "pre_shared_key" extension, it MUST contain both a "signature_algorithms" extension and a "supported_groups" extension. | C | 22.1
| If containing a "supported_groups" extension, it MUST also contain a "key_share" extension, and vice versa. An empty KeyShare.client_shares vector is permitted. | C | 22.1
| TLS 1.3 ServerHello | C | 23.2
| MUST support the use of the "server_name" extension | C | 23.2
9.3. Protocol Invariants |  | C | 22.1
| MUST correctly handle extensible fields | C | 22.1
| A client sending a ClientHello MUST support all parameters advertised in it. Otherwise, the server may fail to interoperate by selecting one of those parameters. | C | 22.1
| A server receiving a ClientHello MUST correctly ignore all unrecognized cipher suites, extensions, and other parameters. Otherwise, it may fail to interoperate with newer clients. In TLS 1.3, a client receiving a CertificateRequest or NewSessionTicket MUST also ignore all unrecognized extensions. | C | 22.1
| A middlebox which terminates a TLS connection MUST behave as a compliant TLS server | NA |
| A middlebox which forwards ClientHello parameters it does not understand MUST NOT process any messages beyond that ClientHello. It MUST forward all subsequent traffic unmodified. Otherwise, it may fail to interoperate with newer clients and servers. | NA |
B.4. Cipher Suites |  | C | 23
| TLS_AES_128_GCM_SHA256 | C | 22
| TLS_AES_256_GCM_SHA384 | C | 22
| TLS_CHACHA20_POLY1305_SHA256 | C | 22
| TLS_AES_128_CCM_SHA256 | C | 22
| TLS_AES_128_CCM_8_SHA256 | C | 23
C.1. Random Number Generation and Seeding |  | C | 22
C.2. Certificates and Authentication |  | C | 22
C.3. Implementation Pitfalls |  | PC | 22
C.4. Client Tracking Prevention |  | C | 22.2
C.5. Unauthenticated Operation |  | C | 22
D.1. Negotiating with an Older Server |  | C | 22.2
D.2. Negotiating with an Older Client |  | C | 22
D.3. 0-RTT Backward Compatibility |  | NC |
D.4. Middlebox Compatibility Mode |  | C | 23
D.5. Security Restrictions Related to Backward Compatibility |  | C | 22

Table: Standards Compliance

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