Module pka 

Public Key Accelerator (PKA)

This module provides hardware-accelerated public key cryptographic operations using the PKA peripheral. The PKA can accelerate:

• ECDSA: Signature generation and verification
• ECDH: Elliptic Curve Diffie-Hellman key agreement (via scalar multiplication)
• RSA: Encryption, decryption, and signing (via modular exponentiation)
• Arithmetic: Modular operations, Montgomery multiplication

Supported Operations

Operation	Mode	Description
Modular Exponentiation	0x00	RSA encryption/decryption
Montgomery Parameter	0x01	Compute Montgomery parameter for RSA
RSA CRT Exponentiation	0x07	Fast RSA with Chinese Remainder Theorem
Modular Inversion	0x08	Compute modular inverse
ECC Scalar Multiplication	0x20	ECDH key agreement, point multiplication
ECDSA Sign	0x24	Generate ECDSA signatures
ECDSA Verify	0x26	Verify ECDSA signatures
Point Check	0x28	Validate point is on curve

Example - ECDSA Signature Verification (async)

use embassy_stm32::pka::{Pka, EcdsaCurveParams, EcdsaPublicKey, EcdsaSignature};

let mut pka = Pka::new(p.PKA, Irqs);
let params = EcdsaCurveParams::nist_p256();

let public_key = EcdsaPublicKey {
    x: &pub_key_x,
    y: &pub_key_y,
};

let signature = EcdsaSignature {
    r: &sig_r,
    s: &sig_s,
};

let valid = pka.ecdsa_verify(&params, &public_key, &signature, &hash).await?;

For blocking use, swap Pka::new for Pka::new_blocking and call pka.ecdsa_verify_blocking(...) etc. without .await.

RAM scrubbing

Operations do not clear the RAM between calls. After a sensitive operation (one that touched a private key – e.g. ecdsa_sign, ecc_mul with a private scalar, modular_exp with a private exponent), the intermediate values remain in PKA RAM until overwritten. To explicitly scrub the RAM between sensitive operations, call Pka::scrub:

pka.ecdsa_sign(&curve, &priv_key, &k, &hash, &mut sig_r, &mut sig_s).await?;
pka.scrub().await?; // zero the PKA RAM before the next op

Security Notes

• Always use cryptographically secure random numbers for ECDSA k values.
• Validate all public keys before use (call point_check).
• Call Pka::scrub between operations that touch sensitive material.
• Clear sensitive data from caller-owned buffers after use.

Structs

EccPoint

ECC point (for scalar multiplication results)

EccProjectivePoint

ECC point in projective coordinates (X, Y, Z)

EcdsaCurveParams

ECDSA/ECC curve parameters

EcdsaPublicKey

ECDSA public key

EcdsaSignature

ECDSA signature

InterruptHandler

PKA interrupt handler.

ModExpProtectParams

Parameters for modular exponentiation with protection (side-channel resistant)

Pka

PKA driver

RsaCrtParams

RSA CRT parameters for fast decryption

RsaParams

RSA operation parameters

Enums

ComparisonResult

Result of a comparison operation

Error

PKA error

PkaMode

PKA operation modes

Traits

Instance

PKA instance trait.