]> Arm Limited

Hannes.Tschofenig@gmx.net

Arm Limited

Thomas.Fossati@arm.com

Security UTA Internet-Draft This document is a companion to RFC 7925 and defines TLS/DTLS 1.3 profiles for Internet of Things devices. It also updates RFC 7925 with regards to the X.509 certificate profile. Discussion Venues Source for this draft and an issue tracker can be found at .

Introduction This document defines a profile of DTLS 1.3 and TLS 1.3 that offers communication security services for IoT applications and is reasonably implementable on many constrained devices. Profile thereby means that available configuration options and protocol extensions are utilized to best support the IoT environment. For IoT profiles using TLS/DTLS 1.2 please consult . This document re-uses the communication pattern defined in and makes IoT-domain specific recommendations for version 1.3 (where necessary). TLS 1.3 has been re-designed and several previously defined extensions are not applicable to the new version of TLS/DTLS anymore. This clean-up also simplifies this document. Furthermore, many outdated ciphersuites have been omitted from the TLS/DTLS 1.3 specification.

Conventions and 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.

Credential Types In accordance with the recommendations in , a compliant implementation MUST implement TLS_AES_128_CCM_8_SHA256. It SHOULD implement TLS_CHACHA20_POLY1305_SHA256. Pre-shared key based authentication is integrated into the main TLS/DTLS 1.3 specification and has been harmonized with session resumption. A compliant implementation supporting authentication based on certificates and raw public keys MUST support digital signatures with ecdsa_secp256r1_sha256. A compliant implementation MUST support the key exchange with secp256r1 (NIST P-256) and SHOULD support key exchange with X25519. A plain PSK-based TLS/DTLS client or server MUST implement the following extensions:

• Supported Versions,
• Cookie,
• Server Name Indication (SNI),
• Pre-Shared Key,
• PSK Key Exchange Modes, and
• Application-Layer Protocol Negotiation (ALPN).

The SNI extension is discussed in this document and the justification for implementing and using the ALPN extension can be found in . For TLS/DTLS clients and servers implementing raw public keys and/or certificates the guidance for mandatory-to-implement extensions described in Section 9.2 of MUST be followed.

Error Handling TLS 1.3 simplified the Alert protocol but the underlying challenge in an embedded context remains unchanged, namely what should an IoT device do when it encounters an error situation. The classical approach used in a desktop environment where the user is prompted is often not applicable with unattended devices. Hence, it is more important for a developer to find out from which error cases a device can recover from.

Session Resumption TLS 1.3 has built-in support for session resumption by utilizing PSK-based credentials established in an earlier exchange.

 Compression TLS 1.3 does not have support for compression of application data traffic, as offered by previous versions of TLS. Applications are therefore responsible for transmitting payloads that are either compressed or use a more efficient encoding otherwise. With regards to the handshake itself, various strategies have been applied to reduce the size of the exchanged payloads. TLS and DTLS 1.3 use less overhead, depending on the type of key confirmations, when compared to previous versions of the protocol. Additionally, the work on Compact TLS (cTLS) has taken compression of the handshake a step further by utilizing out-of-band knowledge between the communication parties to reduce the amount of data to be transmitted at each individual handshake, among applying other techniques.

 Perfect Forward Secrecy TLS 1.3 allows the use of PFS with all ciphersuites since the support for it is negotiated independently.

Keep-Alive The discussion in Section 10 of is applicable.

Timeouts The recommendation in Section 11 of is applicable. In particular this document RECOMMENDED to use an initial timer value of 9 seconds with exponential back off up to no less then 60 seconds.

 Random Number Generation The discussion in Section 12 of is applicable with one exception: the ClientHello and the ServerHello messages in TLS 1.3 do not contain gmt_unix_time component anymore.

Server Name Indication This specification mandates the implementation of the Server Name Indication (SNI) extension. Where privacy requirements require it, the Encrypted Client Hello extension prevents an on-path attacker to determine the domain name the client is trying to connect to. Note: To avoid leaking DNS lookups from network inspection altogether further protocols are needed, including DoH and DPRIVE . Since the Encrypted Client Hello extension requires use of Hybrid Public Key Encryption (HPKE) and additional protocols require further protocol exchanges and cryptographic operations, there is a certain amount of overhead associated with this privacy property.

 Maximum Fragment Length Negotiation The Maximum Fragment Length Negotiation (MFL) extension has been superseded by the Record Size Limit (RSL) extension . Implementations in compliance with this specification MUST implement the RSL extension and SHOULD use it to indicate their RAM limitations.

Crypto Agility The recommendations in Section 19 of are applicable.

Key Length Recommendations The recommendations in Section 20 of are applicable.

0-RTT Data establishes that:

• Application protocols MUST NOT use 0-RTT data without a profile that defines its use. That profile needs to identify which messages or interactions are safe to use with 0-RTT and how to handle the situation when the server rejects 0-RTT and falls back to 1-RTT.

At the time of writing, no such profile has been defined for CoAP . Therefore 0-RTT MUST NOT be used by CoAP applications.

Certificate Profile This section contains updates and clarifications to the certificate profile defined in . The content of Table 1 of has been split by certificate "type" in order to clarify exactly what requirements and recommendations apply to which entity in the PKI hierarchy.

All Certificates

Version Certificates MUST be of type X.509 v3.

Serial Number CAs SHALL generate non-sequential Certificate serial numbers greater than zero (0) containing at least 64 bits of output from a CSPRNG (cryptographically secure pseudo-random number generator).

Signature The signature MUST be ecdsa-with-SHA256 or stronger .

Issuer Contains the DN of the issuing CA.

 Validity No maximum validity period is mandated. Validity values are expressed in notBefore and notAfter fields, as described in Section 4.1.2.5 of . In particular, values MUST be expressed in Greenwich Mean Time (Zulu) and MUST include seconds even where the number of seconds is zero. Note that the validity period is defined as the period of time from notBefore through notAfter, inclusive. This means that a hypothetical certificate with a notBefore date of 9 June 2021 at 03:42:01 and a notAfter date of 7 September 2021 at 03:42:01 becomes valid at the beginning of the :01 second, and only becomes invalid at the :02 second, a period that is 90 days plus 1 second. So for a 90-day, notAfter must actually be 03:42:00. In many cases it is necessary to indicate that a certificate does not expire. This is likely to be the case for manufacturer-provisioned certificates. RFC 5280 provides a simple solution to convey the fact that a certificate has no well-defined expiration date by setting the notAfter to the GeneralizedTime value of 99991231235959Z. Some devices might not have a reliable source of time and for those devices it is also advisable to use certificates with no expiration date and to let a device management solution manage the lifetime of all the certificates used by the device. While this approach does not utilize certificates to its widest extent, it is a solution that extends the capabilities offered by a raw public key approach.

 subjectPublicKeyInfo The SubjectPublicKeyInfo structure indicates the algorithm and any associated parameters for the ECC public key. This profile uses the id-ecPublicKey algorithm identifier for ECDSA signature keys, as defined and specified in .

Root CA Certificate

• basicConstraints MUST be present and MUST be marked critical. The cA field MUST be set true. The pathLenConstraint field SHOULD NOT be present.
• keyUsage MUST be present and MUST be marked critical. Bit position for keyCertSign MUST be set.
• extendedKeyUsage MUST NOT be present.

Subordinate CA Certificate

• basicConstraints MUST be present and MUST be marked critical. The cA field MUST be set true. The pathLenConstraint field MAY be present.
• keyUsage MUST be present and MUST be marked critical. Bit position for keyCertSign MUST be set.
• extendedKeyUsage MUST NOT be present.

End Entity Certificate

• extendedKeyUsage MUST be present and contain at least one of id-kp-serverAuth or id-kp-clientAuth.
• keyUsage MAY be present and contain one of digitalSignature or keyAgreement.
• Domain names MUST NOT be encoded in the subject commonName, instead they MUST be encoded in a subjectAltName of type DNS-ID. Domain names MUST NOT contain wildcard (*) characters. subjectAltName MUST NOT contain multiple names.

Client Certificate Subject The requirement in Section 4.4.2 of to only use EUI-64 for client certificates is lifted. If the EUI-64 format is used to identify the subject of a client certificate, it MUST be encoded in a subjectAltName of type DNS-ID as a string of the form HH-HH-HH-HH-HH-HH-HH-HH where 'H' is one of the symbols '0'-'9' or 'A'-'F'.

Certificate Revocation Checks The considerations in Section 4.4.3 of hold. Since the publication of RFC 7925 the need for firmware update mechanisms has been reinforced and the work on standardizing a secure and interoperable firmware update mechanism has made substantial progress, see . RFC 7925 recommends to use a software / firmware update mechanism to provision devices with new trust anchors. The use of device management protocols for IoT devices, which often include an onboarding or bootstrapping mechanism, has also seen considerable uptake in deployed devices and these protocols, some of which are standardized, allow provision of certificates on a regular basis. This enables a deployment model where IoT device utilize end-entity certificates with shorter lifetime making certificate revocation protocols, like OCSP and CRLs, less relevant. Hence, instead of performing certificate revocation checks on the IoT device itself this specification recommends to delegate this task to the IoT device operator and to take the necessary action to allow IoT devices to remain operational.

Certificate Overhead In a public key-based key exchange, certificates and public keys are a major contributor to the size of the overall handshake. For example, in a regular TLS 1.3 handshake with minimal ECC certificates and no subordinate CA utilizing the secp256r1 curve with mutual authentication, around 40% of the entire handshake payload is consumed by the two exchanged certificates. Hence, it is not surprising that there is a strong desire to reduce the size of certificates and certificate chains. This has lead to various standardization efforts. Here is a brief summary of what options an implementer has to reduce the bandwidth requirements of a public key-based key exchange:

• Use elliptic curve cryptography (ECC) instead of RSA-based certificate due to the smaller certificate size.
• Avoid deep and complex CA hierarchies to reduce the number of subordinate CA certificates that need to be transmitted.
• Pay attention to the amount of information conveyed inside certificates.
• Use session resumption to reduce the number of times a full handshake is needed. Use Connection IDs , when possible, to enable long-lasting connections.
• Use the TLS cached info extension to avoid sending certificates with every full handshake.
• Use client certificate URLs instead of full certificates for clients.
• Use certificate compression as defined in .
• Use alternative certificate formats, where possible, such as raw public keys or CBOR-encoded certificates .

The use of certificate handles, as introduced in cTLS , is a form of caching or compressing certificates as well. Whether to utilize any of the above extensions or a combination of them depends on the anticipated deployment environment, the availability of code, and the constraints imposed by already deployed infrastructure (e.g., CA infrastructure, tool support).

Ciphersuites Section 4.5.3 of flags AES-CCM with 8-octet authentication tags (CCM_8) as unsuitable for general use with DTLS. In fact, due to its low integrity limits (i.e., a high sensitivity to forgeries), endpoints that negotiate ciphersuites based on such AEAD are susceptible to a trivial DoS. (See also Section 5.3 and 5.4 of for further discussion on this topic, as well as references to the analysis supporting these conclusions.) Specifically, warns that:

• "TLS_AES_128_CCM_8_SHA256 MUST NOT be used in DTLS without additional safeguards against forgery. Implementations MUST set usage limits for AEAD_AES_128_CCM_8 based on an understanding of any additional forgery protections that are used."

Since all the ciphersuites mandated by and are based on CCM_8, there is no stand-by ciphersuite to use for applications that want to avoid the security and availability risks associated with CCM_8 while retaining interoperability with the rest of the ecosystem. In order to ameliorate the situation, this document RECOMMENDS that implementations support the following two ciphersuites:

• TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
• TLS_ECDHE_ECDSA_WITH_AES_128_CCM

and offer them as their first choice. These ciphersuites provide confidentiality and integrity limits that are considered acceptable in the most general settings. For the details on the exact bounds of both ciphersuites see Section 4.5.3 of . Note that the GCM-based ciphersuite offers superior interoperability with cloud services at the cost of a slight increase in the wire and peak RAM footprints. When the GCM-based ciphersuite is used with TLS 1.2, the recommendations in Section 6.2.1 of related to deterministic nonce generation apply. In addition, the integrity limits on key usage detailed in Section 4.4 of also apply.

Fault Attacks on Deterministic Signature Schemes A number of passive side-channel attacks as well as active fault-injection attacks (e.g., ) have been demonstrated that allow a malicious third party to gain information about the signing key if a fully deterministic signature scheme (e.g., ECDSA or EdDSA ) is used. Most of these attacks assume physical access to the device and are therefore especially relevant to smart cards as well as IoT deployments with poor or non-existent physical security. In this security model, it is recommended to combine both randomness and determinism, for example, as described in .

Open Issues A list of open issues can be found at https://github.com/thomas-fossati/draft-tls13-iot/issues

Security Considerations This entire document is about security.

IANA Considerations This document makes no requests to IANA.

References Normative References 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. 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. Intuit independent arm Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are used to protect data exchanged over a wide range of application protocols, and can also form the basis for secure transport protocols. Over the years, the industry has witnessed several serious attacks on TLS and DTLS, including attacks on the most commonly used cipher suites and their modes of operation. This document provides the latest recommendations for ensuring the security of deployed services that use TLS and DTLS. These recommendations are applicable to the majority of use cases. An earlier version of this document was published as RFC 7525 when the industry was in the midst of its transition to TLS 1.2. Years later this transition is largely complete and TLS 1.3 is widely available. This document updates the guidance given the new environment and obsoletes RFC 7525. In addition, the document updates RFC 5288 and RFC 6066 in view of recent attacks. 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. A common design pattern in Internet of Things (IoT) deployments is the use of a constrained device that collects data via sensors or controls actuators for use in home automation, industrial control systems, smart cities, and other IoT deployments. This document defines a Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) 1.2 profile that offers communications security for this data exchange thereby preventing eavesdropping, tampering, and message forgery. The lack of communication security is a common vulnerability in IoT products that can easily be solved by using these well-researched and widely deployed Internet security protocols. 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. An extension to Transport Layer Security (TLS) is defined that allows endpoints to negotiate the maximum size of protected records that each will send the other. This replaces the maximum fragment length extension defined in RFC 6066. This document updates RFC 3279 to specify algorithm identifiers and ASN.1 encoding rules for the Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA) digital signatures when using SHA-224, SHA-256, SHA-384, or SHA-512 as the hashing algorithm. This specification applies to the Internet X.509 Public Key infrastructure (PKI) when digital signatures are used to sign certificates and certificate revocation lists (CRLs). This document also identifies all four SHA2 hash algorithms for use in the Internet X.509 PKI. [STANDARDS-TRACK] This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] This document specifies the syntax and semantics for the Subject Public Key Information field in certificates that support Elliptic Curve Cryptography. This document updates Sections 2.3.5 and 5, and the ASN.1 module of "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3279. [STANDARDS-TRACK] Informative References This document specifies the Connection ID (CID) construct for the Datagram Transport Layer Security (DTLS) protocol version 1.2. A CID is an identifier carried in the record layer header that gives the recipient additional information for selecting the appropriate security association. In "classical" DTLS, selecting a security association of an incoming DTLS record is accomplished with the help of the 5-tuple. If the source IP address and/or source port changes during the lifetime of an ongoing DTLS session, then the receiver will be unable to locate the correct security context. The new ciphertext record format with the CID also provides content type encryption and record layer padding. This document updates RFC 6347. The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation. CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments. Mozilla Cisco Arm Limited This document specifies a "compact" version of TLS 1.3. It is isomorphic to TLS 1.3 but saves space by trimming obsolete material, tighter encoding, a template-based specialization technique, and alternative cryptographic techniques. cTLS is not directly interoperable with TLS 1.3, but it should eventually be possible for a cTLS/TLS 1.3 server to exist and successfully interoperate. RTFM, Inc. Fastly Cloudflare Cloudflare This document describes a mechanism in Transport Layer Security (TLS) for encrypting a ClientHello message under a server public key. 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/tlswg/draft-ietf-tls-esni (https://github.com/tlswg/draft-ietf-tls-esni). This document defines a protocol for sending DNS queries and getting DNS responses over HTTPS. Each DNS query-response pair is mapped into an HTTP exchange. This document describes the use of Transport Layer Security (TLS) to provide privacy for DNS. Encryption provided by TLS eliminates opportunities for eavesdropping and on-path tampering with DNS queries in the network, such as discussed in RFC 7626. In addition, this document specifies two usage profiles for DNS over TLS and provides advice on performance considerations to minimize overhead from using TCP and TLS with DNS. This document focuses on securing stub-to-recursive traffic, as per the charter of the DPRIVE Working Group. It does not prevent future applications of the protocol to recursive-to-authoritative traffic. DNS queries and responses are visible to network elements on the path between the DNS client and its server. These queries and responses can contain privacy-sensitive information, which is valuable to protect. This document proposes the use of Datagram Transport Layer Security (DTLS) for DNS, to protect against passive listeners and certain active attacks. As latency is critical for DNS, this proposal also discusses mechanisms to reduce DTLS round trips and reduce the DTLS handshake size. The proposed mechanism runs over port 853. Cisco Inria Inria Cloudflare This document describes a scheme for hybrid public key encryption (HPKE). This scheme provides a variant of public key encryption of arbitrary-sized plaintexts for a recipient public key. It also includes three authenticated variants, including one that authenticates possession of a pre-shared key and two optional ones that authenticate possession of a key encapsulation mechanism (KEM) private key. HPKE works for any combination of an asymmetric KEM, key derivation function (KDF), and authenticated encryption with additional data (AEAD) encryption function. Some authenticated variants may not be supported by all KEMs. We provide instantiations of the scheme using widely used and efficient primitives, such as Elliptic Curve Diffie-Hellman (ECDH) key agreement, HMAC-based key derivation function (HKDF), and SHA2. This document is a product of the Crypto Forum Research Group (CFRG) in the IRTF. Arm Limited Arm Limited Linaro Consultant Vulnerabilities in Internet of Things (IoT) devices have raised the need for a reliable and secure firmware update mechanism suitable for devices with resource constraints. Incorporating such an update mechanism is a fundamental requirement for fixing vulnerabilities, but it also enables other important capabilities such as updating configuration settings and adding new functionality. In addition to the definition of terminology and an architecture, this document provides the motivation for the standardization of a manifest format as a transport-agnostic means for describing and protecting firmware updates. Transport Layer Security (TLS) handshakes often include fairly static information, such as the server certificate and a list of trusted certification authorities (CAs). This information can be of considerable size, particularly if the server certificate is bundled with a complete certificate chain (i.e., the certificates of intermediate CAs up to the root CA). This document defines an extension that allows a TLS client to inform a server of cached information, thereby enabling the server to omit already available information. This document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK] Cloudflare, Inc. Google In TLS handshakes, certificate chains often take up the majority of the bytes transmitted. This document describes how certificate chains can be compressed to reduce the amount of data transmitted and avoid some round trips. This document specifies a new certificate type and two TLS extensions for exchanging raw public keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS). The new certificate type allows raw public keys to be used for authentication. Ericsson AB Ericsson AB RISE AB RISE AB Nexus Group This document specifies a CBOR encoding of X.509 certificates. The resulting certificates are called C509 Certificates. The CBOR encoding supports a large subset of RFC 5280 and all certificates compatible with the RFC 7925, IEEE 802.1AR (DevID), CNSA, RPKI, GSMA eUICC, and CA/Browser Forum Baseline Requirements profiles. When used to re-encode DER encoded X.509 certificates, the CBOR encoding can in many cases reduce the size of RFC 7925 profiled certificates with over 50%. The CBOR encoded structure can alternatively be signed directly ("natively signed"), which does not require re- encoding for the signature to be verified. The document also specifies C509 COSE headers, a C509 TLS certificate type, and a C509 file format. ETH Zurich Mozilla Cloudflare An Authenticated Encryption with Associated Data (AEAD) algorithm provides confidentiality and integrity. Excessive use of the same key can give an attacker advantages in breaking these properties. This document provides simple guidance for users of common AEAD functions about how to limit the use of keys in order to bound the advantage given to an attacker. It considers limits in both single- and multi-key settings. This document defines a deterministic digital signature generation procedure. Such signatures are compatible with standard Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA) digital signatures and can be processed with unmodified verifiers, which need not be aware of the procedure described therein. Deterministic signatures retain the cryptographic security features associated with digital signatures but can be more easily implemented in various environments, since they do not need access to a source of high-quality randomness. This document describes elliptic curve signature scheme Edwards-curve Digital Signature Algorithm (EdDSA). The algorithm is instantiated with recommended parameters for the edwards25519 and edwards448 curves. An example implementation and test vectors are provided. Ericsson Ericsson Ericsson Deterministic elliptic-curve signatures such as deterministic ECDSA and EdDSA have gained popularity over randomized ECDSA as their security do not depend on a source of high-quality randomness. Recent research has however found that implementations of these signature algorithms may be vulnerable to certain side-channel and fault injection attacks due to their determinism. One countermeasure to such attacks is to re-add randomness to the otherwise deterministic calculation of the per-message secret number. This document updates RFC 6979 and RFC 8032 to recommend constructions with additional randomness for deployments where side-channel attacks and fault injection attacks are a concern. The updates are invisible to the validator of the signature and compatible with existing ECDSA and EdDSA validators.

Acknowledgments We would like to thank Ben Kaduk and John Mattsson.