Importing partial RSA private keys

[gilles-peskine-arm]

The PSA API only supports a single import format for RSA private keys, which requires both the private exponent and the CRT parameters (p, q, dp, dq, u). This is a feature regression from Mbed TLS ≤3.x, where the low-level function mbedtls_rsa_complete is part of the public API and is capable of reconstructing partial RSA keys in most cases where it is possible.

(Note that this isn't about concrete formats, but about the information included in the representation. The pk module will continue to support both PKCS#1 and PKCS#8 formats in DER or PEM representations.)

Should TF-PSA-Crypto offer a way to import partial RSA private keys, e.g. where the CRT parameters are missing or where the private exponent is missing?

Mailing list thread: https://lists.trustedfirmware.org/archives/list/mbed-tls@lists.trustedfirmware.org/thread/FDDZVLDUVKOZAN523EJXX2LPET7LATS3/

[gilles-peskine-arm]

Architectural decision: we are not going to provide a way to import partial RSA keys in TF-PSA-Crypto 1.0. We can remove the corresponding code.