]> Ericsson AB

SE-164 80 Stockholm Sweden john.mattsson@ericsson.com

Security Transport Layer Security next generation unicorn sparkling distributed ledger Massive pervasive monitoring attacks using key exfiltration and made possible by key exchange without forward secrecy have been reported. If key exchange without Diffie-Hellman is used, static exfiltration of the long-term authentication keys enables passive attackers to compromise all past and future connections. Malicious actors can get access to long-term keys in different ways: physical attacks, hacking, social engineering attacks, espionage, or by simply demanding access to keying material with or without a court order. Exfiltration attacks are a major cybersecurity threat. If NULL encryption is used an on-path attacker can read all application data. The use of psk_ke and NULL encryption are not following zero trust principles of minimizing the impact of breach and governments have already made deadlines for their deprecation. This document evaluates TLS pre-shared key exchange modes, (EC)DHE groups, signature algorithms, and cipher suites and downgrades many entries to "N" and "D" where "D" indicates that the entries are "Discouraged". About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Transport Layer Security Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction added a Recommended column to many of the TLS registries. The Recommended column did originally non-normatively indicate parameters that are generally recommended for implementations to support. The meaning of the column was changed by to indicate that the IETF has consensus that the item is RECOMMENDED, i.e., using normative language. also introduced a third value "D" indicating that an item is discouraged and SHOULD NOT or MUST NOT be used. This means that all current values need to be reevaluated. The current values also need to be reevaluated as attacks, government requirements, and best practices have changed in the more than 4 years since and were published. This document evaluates TLS pre-shared key exchange modes, (EC)DHE groups, signature algorithms, and cipher suites and downgrades many entries to "N" and "D" where "D" indicates that the entries are "Discouraged". While TLS 1.2 is obsolete and two NIST compatible implementations will therefore never negotiate TLS 1.2 after January 1, 2024, DTLS 1.3 was recently published. DTLS 1.2 will therefore continue to be allowed for several years and a distinction between recommended and discouraged parameters is warranted.

Terminology 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 when, and only when, they appear in all capitals, as shown here.

Key Exchange Without Forward Secrecy Key exchange without forward secrecy enables passive monitoring . Massive pervasive monitoring attacks using key exfiltration and made possible by key exchange without forward secrecy have been reported , and many more have likely happened without ever being reported. If key exchange without Diffie-Hellman is used, access to the long-term authentication keys enables passive attackers to compromise all past and future connections. Malicious actors can get access to long-term keys in different ways: physical attacks, hacking, social engineering attacks, espionage, or by simply demanding access to keying material with or without a court order. Exfiltration attacks are a major cybersecurity threat . All cipher suites without forward secrecy have been marked as NOT RECOMMENDED in TLS 1.2 , and static RSA and DH are forbidden in TLS 1.3 . A large number of TLS profiles and implementations forbid the use of key exchange without Diffie-Hellman.

• ANSSI states that for all versions of TLS: "The perfect forward secrecy property must be ensured" .
• The general 3GPP TLS 1.2 profile follows and states: "Only cipher suites with AEAD (e.g., GCM) and PFS (e.g. ECDHE, DHE) shall be supported" .
• BoringSSL has chosen to not implement psk_ke, so that TLS 1.3 resumption always incorporates fresh key material .

Unfortunately, TLS 1.3 allows key exchange without forward secrecy in both full handshakes and resumption handshakes with the psk_ke. As stated in , psk_ke does not fulfill one of the fundamental TLS 1.3 security properties, namely "Forward secret with respect to long-term keys". When the PSK is a group key, which is now formally allowed in TLS 1.3 , psk_ke fails yet another one of the fundamental TLS 1.3 security properties, namely "Secrecy of the session keys" . PSK authentication has yet another big inherent weakness as it often does not provide "Protection of endpoint identities". It could be argued that PSK authentication should be not recommended solely based on this significant privacy weakness. The 3GPP radio access network that to a large degree relies on PSK are fixing the vulnerabilities by augmenting PSK with ECIES and ECDHE, see Annex C of and . Together with ffdhe2048 and rsa_pkcs1, psk_ke is one of the bad apples in the standards track TLS 1.3 fruit basket. Organizations like BSI has already produced recommendations regarding its deprecation.

• BSI states regarding psk_ke that "This mode should only be used in special applications after consultation of an expert." and has set a deadline that use is only allowed until 2026.

Two essential zero trust principles are to assume that breach is inevitable or has likely already occurred , and to minimize impact when breach occur . One type of breach is key compromise or key exfiltration. Different types of exfiltration are defined and discussed in . Static exfiltration where the keys are transferred once has a lower risk profile than dynamic exfiltration where keying material or content is transferred to the attacker frequently. Forcing an attacker to do dynamic exfiltration minimizes the impact of breach and should be considered best practice. This significantly increases the risk of discovery for the attacker. One way to force an attacker to do dynamic exfiltration is to frequently rerun ephemeral Diffie-Hellman. For IPsec, ANSSI recommends enforcing periodic rekeying with ephemeral Diffie-Hellman, e.g., every hour and every 100 GB of data, in order to limit the impact of a key compromise. This should be considered best practice for all protocols and systems. The Double Ratchet Algorithm in the Signal protocol enables very frequent use of ephemeral Diffie-Hellman. The practice of frequently rerunning ephemeral Diffie-Hellman follows directly from the two zero trust principles mentioned above. In TLS 1.3, the application_traffic_secret can be rekeyed using key_update, a resumption handshake, or a full handshake. The term forward secrecy is not very specific, and it is often better to talk about the property that compromise of key A does not lead to compromise of key B. illustrates the impact of some examples of static key exfiltration when psk_ke, key_update, and (ec)dhe are used for rekeying. Each time period T uses a single application_traffic_secret. means that the attacker has access to the application_traffic_secret in that time period and can passively eavesdrop on the communication. means that the attacker does not have access to the application_traffic_secret. Exfiltration and frequently rerunning EC(DHE) is discussed in Appendix F of .

Impact of static key exfiltration in time period T3 when psk_ke, key_update, and (ec)dhe are used. rekeying with key_update static exfiltration of application_traffic_secret in T₃: +-----+-----+-----+-----+-----+-----+-----+-----+ +-----+-----+ | ✔ | ✔ | ✔ | ✘ | ✘ | ✘ | ✘ | ✘ | ... | ✘ | ✘ | +-----+-----+-----+-----+-----+-----+-----+-----+ +-----+-----+ T₀ T₁ T₂ T₃ T₄ T₅ T₆ T₇ ... Tₙ₋₁ Tₙ <---------------------------------------------> rekeying with (ec)dhe static exfiltration of all keys in T₃: +-----+-----+-----+-----+-----+-----+-----+-----+ +-----+-----+ | ✔ | ✔ | ✔ | ✘ | ✔ | ✔ | ✔ | ✔ | ... | ✔ | ✔ | +-----+-----+-----+-----+-----+-----+-----+-----+ +-----+-----+ T₀ T₁ T₂ T₃ T₄ T₅ T₆ T₇ ... Tₙ₋₁ Tₙ <---> ]]>

Modern ephemeral key exchange algorithms like x25519 are very fast and have small message overhead. The public keys are 32 bytes long and the cryptographic operations take 53 microseconds per endpoint on a single core AMD Ryzen 5 5560U . Ephemeral key exchange with the quantum-resistant algorithm Kyber that NIST will standardize is even faster. For the current non-standardized version of Kyber512 the cryptographic operations take 12 microseconds for the client and 8 microseconds for the server . Unfortunately, psk_ke is marked as "Recommended" in the IANA PskKeyExchangeMode registry. This may severely weaken security in deployments following the "Recommended" column. Introducing TLS 1.3 in 3GPP had the unfortunate and surprising effect of drastically lowering the minimum security when TLS is used with PSK authentication. Some companies in 3GPP have been unwilling to mark psk_ke as not recommended as it is so clearly marked as "Recommended" by the IETF. By labeling psk_ke as "Recommended", IETF is legitimizing and implicitly promoting bad security practice. This document sets the "Recommended" value of psk_ke to "D" indicating that it is "Discouraged". describes and classifies prohibited TLS 1.2 cipher suites without forward secrecy. This document sets the "Recommended" value of all cipher suites listed in Appendix A of as well as TLS_PSK_WITH_CHACHA20_POLY1305_SHA256 to "D" indicating that they are "Discouraged".

Cipher Suites with NULL Encryption Cipher suites with NULL encryption enables passive monitoring and were completely removed from TLS 1.3 . Unfortunately, the independent stream document reintroduced cipher suites with NULL Encryption in TLS 1.3 even though NULL encryption violates several of the fundamental TLS 1.3 security properties, namely "Protection of endpoint identities", "Confidentiality", and "Length concealment". Some companies in 3GPP have already suggested to use in QUIC but luckily this is forbidden by and hopefully it will stay like that. Modern encryption algorithms like AES-GCM are very fast and have small message overhead. Upcoming algorithms like AEGIS is much faster than AES-GCM . NULL encryption has no raison d'tre in two-party protocols. Two essential zero trust principles are to assume that breach is inevitable or has likely already occurred , and to minimize impact when breach occur . One type of breach is an on-path attacker present on the enterprise network. In , NIST states as the first basic assumption for network connectivity for any organization that utilizes zero trust is that:

• "The entire enterprise private network is not considered an implicit trust zone. Assets should always act as if an attacker is present on the enterprise network, and communication should be done in the most secure manner available. This entails actions such as authenticating all connections and encrypting all traffic."

This document sets the "Recommended" value of TLS_SHA256_SHA256 and TLS_SHA384_SHA384 to "D" indicating that they are "Discouraged".

Obsolete Key Exchange Government organizations like NIST, ANSSI, BSI, and NSA have already produced recommendations regarding the deprecation of key exchange algorithms with less than 128-bit security such as ffdhe2048. NIST and ANSSI only allow 2048-bit Finite Field Diffie-Hellman if the application data does not have to be protected after 2030. If the application data had a security life of ten years, NIST and ANSSI allowed use of ffdhe2048 until December 31, 2020. BSI allowed use of ffdhe2048 up to the year 2022. The Commercial National Security Algorithm Suite (CNSA) forbids the use of ffdhe2048. ECDHE groups that offer less than 128-bit security are forbidden to use in TLS 1.3. This document sets the "Recommended" value of ffdhe2048, secp160k1, secp160r1, secp160r2, sect163k1, sect163r1, sect163r2, secp192k1, secp192r1, sect193r1, sect193r2, secp224k1, secp224r1m sect233k1, sect233r1, and sect239k1 to "D" indicating that they are "Discouraged". describes and classifies cipher suites with obsolete key exchange methods in TLS 1.2 but does not downgrade the "Recommended" value. This document sets the "Recommended" value of all cipher suites listed in Appendix A of to "D" indicating that they are "Discouraged".

Signature Algorithms with PKCS #1 v1.5 Padding or SHA-1 Recommendations regarding RSASSA-PKCS1-v1_5 in certificates varies. The RSA Cryptography Specifications specifies that "RSASSA-PSS is REQUIRED in new applications. RSASSA-PKCS1-v1_5 is included only for compatibility with existing applications.". BSI allows use of the PKCS #1 v1.5 padding scheme in certificates up to the year 2025. The Commercial National Security Algorithm (CNSA) requires offer of rsa_pkcs1_sha384 in certificates. This document sets the "Recommended" value of rsa_pkcs1_sha256, rsa_pkcs1_sha384, and rsa_pkcs1_sha512 to "N". forbids the use of RSASSA-PKCS1-v1_5 in signed TLS handshake messages. registered new RSASSA-PKCS1-v1_5 signature algorithms for use in signed TLS 1.3 handshake messages. This document sets the "Recommended" value of rsa_pkcs1_sha256_legacy, rsa_pkcs1_sha384_legacy, and rsa_pkcs1_sha512_legacy to "D" indicating that they are "Discouraged". labels rsa_pkcs1_sha1 and ecdsa_sha1 as legacy algorithms which are being deprecated and that endpoints SHOULD NOT or MUST NOT negotiate. This document sets the "Recommended" value of rsa_pkcs1_sha1 and ecdsa_sha1 to "D" indicating that they are "Discouraged".

IANA Considerations

TLS PskKeyExchangeMode IANA is requested to update the TLS PskKeyExchangeMode registry under the Transport Layer Security (TLS) Parameters heading. For the following entry the "Recommended" value has been set to "D" indicating that the item is "Discouraged". Downgraded TLS PSK Key Exchange Modes

Description	Recommended
psk_ke	D

TLS Cipher Suites IANA is requested to update the TLS Cipher Suites registry under the Transport Layer Security (TLS) Parameters heading. For all cipher suites listed in Appendix A of , all cipher suites listed in Appendix A of , and the following entries the "Recommended" value have been set to "D" indicating that the items are "Discouraged". Downgraded TLS Cipher Suites

Description	Recommended
TLS_SHA256_SHA256	D
TLS_SHA384_SHA384	D
TLS_PSK_WITH_CHACHA20_POLY1305_SHA256	D

TLS Supported Groups IANA is requested to update the TLS Supported Groups registry under the Transport Layer Security (TLS) Parameters heading. For the following entries the "Recommended" value have been set to "D" indicating that the items are "Discouraged". Downgraded TLS Supported Groups

Description	Recommended
sect163k1	D
sect163r1	D
sect163r2	D
sect193r1	D
sect193r2	D
sect233k1	D
sect233r1	D
sect239k1	D
secp160k1	D
secp160r1	D
secp160r2	D
secp192k1	D
secp192r1	D
secp224k1	D
secp224r1	D
ffdhe2048	D

TLS SignatureScheme IANA is requested to update the TLS SignatureScheme registry under the Transport Layer Security (TLS) Parameters heading. For the following entries the "Recommended" value have been set to "N" or "D" where "D" indicates that the items are "Discouraged". Downgraded TLS Signature Schemes

Description	Recommended
rsa_pkcs1_sha1	D
ecdsa_sha1	D
rsa_pkcs1_sha256	N
rsa_pkcs1_sha256_legacy	D
rsa_pkcs1_sha384	N
rsa_pkcs1_sha384_legacy	D
rsa_pkcs1_sha512	N
rsa_pkcs1_sha512_legacy	D

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2 (HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduced latency by introducing field compression and allowing multiple concurrent exchanges on the same connection. This document obsoletes RFCs 7540 and 8740. This document specifies version 1.3 of the Datagram Transport Layer Security (DTLS) protocol. DTLS 1.3 allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. The DTLS 1.3 protocol is based on the Transport Layer Security (TLS) 1.3 protocol and provides equivalent security guarantees with the exception of order protection / non-replayability. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document obsoletes RFC 6347. Apple, Inc. This document makes several prescriptions regarding the following key exchange methods in TLS, most of which have been superseded by better options: Venafi sn3rd This document describes a number of changes to TLS and DTLS IANA registries that range from adding notes to the registry all the way to changing the registration policy. These changes were mostly motivated by WG review of the TLS- and DTLS-related registries undertaken as part of the TLS 1.3 development process. This document obsoletes RFC 8447 and updates the following RFCs: 3749, 5077, 4680, 5246, 5705, 5878, 6520, and 7301. Informative References This memo describes the use of the Advanced Encryption Standard (AES) in Galois/Counter Mode (GCM) as a Transport Layer Security (TLS) authenticated encryption operation. GCM provides both confidentiality and data origin authentication, can be efficiently implemented in hardware for speeds of 10 gigabits per second and above, and is also well-suited to software implementations. This memo defines TLS cipher suites that use AES-GCM with RSA, DSA, and Diffie-Hellman-based key exchange mechanisms. [STANDARDS-TRACK] Pervasive monitoring is a technical attack that should be mitigated in the design of IETF protocols, where possible. Since the initial revelations of pervasive surveillance in 2013, several classes of attacks on Internet communications have been discovered. In this document, we develop a threat model that describes these attacks on Internet confidentiality. We assume an attacker that is interested in undetected, indiscriminate eavesdropping. The threat model is based on published, verified attacks. This memo specifies two elliptic curves over prime fields that offer a high level of practical security in cryptographic applications, including Transport Layer Security (TLS). These curves are intended to operate at the ~128-bit and ~224-bit security level, respectively, and are generated deterministically based on a list of required properties. This document provides recommendations for the implementation of public-key cryptography based on the RSA algorithm, covering cryptographic primitives, encryption schemes, signature schemes with appendix, and ASN.1 syntax for representing keys and for identifying the schemes. This document represents a republication of PKCS #1 v2.2 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series. By publishing this RFC, change control is transferred to the IETF. This document also obsoletes RFC 3447. This document describes a number of changes to TLS and DTLS IANA registries that range from adding notes to the registry all the way to changing the registration policy. These changes were mostly motivated by WG review of the TLS- and DTLS-related registries undertaken as part of the TLS 1.3 development process. This document updates the following RFCs: 3749, 5077, 4680, 5246, 5705, 5878, 6520, and 7301. This document describes how Transport Layer Security (TLS) is used to secure QUIC. This document defines the use of cipher suites for TLS 1.3 based on Hashed Message Authentication Code (HMAC). Using these cipher suites provides server and, optionally, mutual authentication and data authenticity, but not data confidentiality. Cipher suites with these properties are not of general applicability, but there are use cases, specifically in Internet of Things (IoT) and constrained environments, that do not require confidentiality of exchanged messages while still requiring integrity protection, server authentication, and optional client authentication. This document gives examples of such use cases, with the caveat that prior to using these integrity-only cipher suites, a threat model for the situation at hand is needed, and a threat analysis must be performed within that model to determine whether the use of integrity-only cipher suites is appropriate. The approach described in this document is not endorsed by the IETF and does not have IETF consensus, but it is presented here to enable interoperable implementation of a reduced-security mechanism that provides authentication and message integrity without supporting confidentiality. This document defines a base profile for TLS protocol versions 1.2 and 1.3 as well as DTLS protocol versions 1.2 and 1.3 for use with the US Commercial National Security Algorithm (CNSA) Suite. The profile applies to the capabilities, configuration, and operation of all components of US National Security Systems that use TLS or DTLS. It is also appropriate for all other US Government systems that process high-value information. The profile is made publicly available here for use by developers and operators of these and any other system deployments. This document provides usage guidance for external Pre-Shared Keys (PSKs) in Transport Layer Security (TLS) 1.3 as defined in RFC 8446. It lists TLS security properties provided by PSKs under certain assumptions, then it demonstrates how violations of these assumptions lead to attacks. Advice for applications to help meet these assumptions is provided. This document also discusses PSK use cases and provisioning processes. Finally, it lists the privacy and security properties that are not provided by TLS 1.3 when external PSKs are used. Ericsson Ericsson Ericsson Ericsson Many different attacks have been reported as part of revelations associated with pervasive surveillance. Some of the reported attacks involved compromising the smart card supply chain, such as attacking SIM card manufacturers and operators in an effort to compromise shared secrets stored on these cards. Since the publication of those reports, manufacturing and provisioning processes have gained much scrutiny and have improved. However, the danger of resourceful attackers for these systems is still a concern. Always assuming breach such as key compromise and minimizing the impact of breach are essential zero-trust principles. This specification updates RFC 9048, the EAP-AKA' authentication method, with an optional extension. Similarly, this specification also updates the earlier version of the EAP-AKA' specification in RFC 5448. The extension, when negotiated, provides Forward Secrecy for the session key generated as a part of the authentication run in EAP- AKA'. This prevents an attacker who has gained access to the long- term pre-shared secret in a SIM card from being able to decrypt any past communications. In addition, if the attacker stays merely a passive eavesdropper, the extension prevents attacks against future sessions. This forces attackers to use active attacks instead. Mozilla This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705, 6066, 7627, and 8422 and obsoletes RFCs 5077, 5246, 6961, and 8446. This document also specifies new requirements for TLS 1.2 implementations. Fastly Inc. Individual Contributor Individual Contributor This document describes AEGIS-128L and AEGIS-256, two AES-based authenticated encryption algorithms designed for high-performance applications. Discussion Venues This note is to be removed before publishing as an RFC. Source for this draft and an issue tracker can be found at https://github.com/jedisct1/draft-aegis-aead. Google LLC This document allocates code points for the use of RSASSA-PKCS1-v1_5 with client certificates in TLS 1.3.

Acknowledgements The authors want to thank , , and for their valuable comments and feedback.