TLS Compressed Elliptic Curve Code Points

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Table of Contents

1. Introduction

Versions of TLS prior to 1.3 allowed for Elliptic Curve Cryptography (ECC) Point Compression negotiation, by sending a however in TLS 1.3 and Section 5.1.2 of [RFC8422], that mechinism was depricated in favor of having one point encoding format for each negotiated curve. Utilizing point compression is important to reduce the size of negotiated curves within TLS in general, but expecially with [I-D.draft-ietf-tls-ctls].¶

The code points defined in this document are intended for use in TLS, dTLS, cTLS, and other similar protocols that negotiate Elliptic Curve Groups for key exchange.¶

2. Supported Groups

This document defines three new new TLS Supported Groups for the compressed forms of secp256r1, secp384r1, and secp521r1 (collectivly colloquially called the NIST Curves). The compressed forms of these groups are indicated by adding a letter 'c' at the end of the descriptive name. The new groups are secp256r1c, secp384r1c, and secp521r1c. TLS groups using compressed NIST curves MUST use these newly defined group idtentifiers.¶

The "TLS Supported Groups" name space is maintained by IANA.¶

enum {
  secp256r1c(tbd1), secp384r1c(tbd2), secp521r1c(tbd3)
} NamedGroup;

struct {
  NamedGroup named_group_list<2..2^16-1>;
} NamedGroupList;

struct {
  CompressedY;
  opaque X[coordinate_length];
} CompressedPointRepresentation;

enum { evenY(2), oddY(3) } CompressedY

3. IANA Considerations

IANA is requested to assign the value tbd1 to secp256r1c, the value tbd2 to secp384r1c, and the value tbd3 to secp521r1c in the "TLS Supported Groups" registry. For these three new supported groups the "DTLS OK" is set to 'Y'. For tbd1 and tbd2 the "Recommended" column is set to 'Y' and for tbd3 the "Recommended" column is set to 'N'.¶

4. Security Considerations

The security considerations of [RFC8422] and [RFC8422] apply to the selection of TLS named groups and the use of the curves specified in this document.¶

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