yuzu/mbedtls
1
0
Fork 0
mirror of https://github.com/yuzu-emu/mbedtls.git synced 2024-10-19 00:41:14 +00:00
Code Issues Packages Projects Releases Wiki Activity

Merge pull request #4133 from gilles-peskine-arm/psa-conditional-inclusion-c-curves

Browse source 
PSA conditional inclusion: add rationale about ECC curves and FFDH groups
This commit is contained in:
Gilles Peskine 2021-02-24 11:18:05 +01:00 committed by GitHub
parent 78fd3b7761 2c5d9e6a32
commit 2ac5f8c04b
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
1 changed files with 11 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

16
docs/proposed/psa-conditional-inclusion-c.md
View file

@ -5,8 +5,6 @@ This document is a proposed interface for deciding at build time which cryptogra
This is currently a proposal for Mbed TLS. It is not currently on track for standardization in PSA.
Time-stamp: "2020/11/26 09:30:50 GMT"
## Introduction
### Purpose of this specification
@ -86,9 +84,17 @@ For each constant or constructor macro of the form `PSA_KEY_TYPE_xxx`, the symbo
For asymmetric cryptography, `PSA_WANT_KEY_TYPE_xxx_KEY_PAIR` determines whether private-key operations are desired, and `PSA_WANT_KEY_TYPE_xxx_PUBLIC_KEY` determines whether public-key operations are desired. `PSA_WANT_KEY_TYPE_xxx_KEY_PAIR` implicitly enables `PSA_WANT_KEY_TYPE_xxx_PUBLIC_KEY`: there is no way to only include private-key operations (which typically saves little code).
#### Configuration symbols for curves
#### Configuration symbols for elliptic curves
For elliptic curve key types, only the specified curves are included. To include a curve, include a symbol of the form **`PSA_WANT_ECC_family_size`**. For example: `PSA_WANT_ECC_SECP_R1_256` for secp256r1, `PSA_WANT_ECC_MONTGOMERY_CURVE25519`. It is an error to require an ECC key type but no curve, and Mbed TLS will reject this at compile time.
For elliptic curve key types, only the specified curves are included. To include a curve, include a symbol of the form **`PSA_WANT_ECC_family_size`**. For example: `PSA_WANT_ECC_SECP_R1_256` for secp256r1, `PSA_WANT_ECC_MONTGOMERY_255` for Curve25519. It is an error to require an ECC key type but no curve, and Mbed TLS will reject this at compile time.
Rationale: this is a deviation of the general principle that `PSA_ECC_FAMILY_xxx` would have a corresponding symbol `PSA_WANT_ECC_FAMILY_xxx`. This deviation is justified by the fact that it is very common to wish to include only certain curves in a family, and that can lead to a significant gain in code size.
#### Configuration symbols for Diffie-Hellman groups
There are no configuration symbols for Diffie-Hellman groups (`PSA_DH_GROUP_xxx`).
Rationale: Finite-field Diffie-Hellman code is usually not specialized for any particular group, so reducing the number of available groups at compile time only saves a little code space. Constrained implementations tend to omit FFDH anyway, so the small code size gain is not important.
#### Configuration symbols for algorithms
@ -195,7 +201,7 @@ The boolean symbol mechanism proposed here can be translated to a list of JSON c
#### Naming of symbols
The names of [elliptic curve symbols](#configuration-symbols-for-curves) are a bit weird: `SECP_R1_256` instead of `SECP256R1`. Should we make them more classical, but less systematic?
The names of [elliptic curve symbols](#configuration-symbols-for-elliptic-curves) are a bit weird: `SECP_R1_256` instead of `SECP256R1`, `MONTGOMERY_255` instead of `CURVE25519`. Should we make them more classical, but less systematic?
#### Impossible combinations