#include "rsa.h"
#include "cdc_log.h"
#include <mbedtls/rsa.h>
#include <mbedtls/bignum.h>
#include <mbedtls/platform_util.h>
#include <esp_random.h>
#include <esp_attr.h>
#include <string.h>

Functions
static int	rsa_rng (void ctx, unsigned char out, size_t len)
	mbedTLS RNG callback backed by the ESP hardware RNG.
static bool	rd_u16 (const uint8_t b, size_t len, size_t pos, uint16_t *out)
	Reads a big-endian u16 from a buffer and advances the cursor.
static bool	rsa_load_ctx (const uint8_t blob, size_t blob_len, mbedtls_rsa_context rsa)
	Parses a private-key blob and imports it into an RSA context. On success the caller owns `rsa` and must free it.
static bool	rsa_serialize (mbedtls_rsa_context rsa, uint8_t out, size_t cap, size_t *out_len)
	Canonically serialises an RSA context (primes + exponent) into a blob.
bool	gpg_rsa_blob_build (uint16_t n_bits, const uint8_t e, size_t e_len, const uint8_t p, size_t p_len, const uint8_t q, size_t q_len, uint8_t blob_out, size_t blob_cap, size_t *blob_len_out)
	Serialises raw RSA components into a private-key blob.
bool	gpg_rsa_generate (uint16_t n_bits, uint8_t blob_out, size_t blob_cap, size_t blob_len_out)
	Generates a fresh RSA key pair and serialises its private blob. The public exponent is fixed to 65537. This is computationally heavy on the ESP32-S3 (seconds to minutes for 4096); the caller is expected to keep the task watchdog fed.
bool	gpg_rsa_blob_public (const uint8_t blob, size_t blob_len, uint8_t n_out, size_t n_cap, size_t n_len_out, uint8_t e_out, size_t e_cap, size_t *e_len_out)
	Extracts the public modulus and exponent from a private-key blob.
bool	gpg_rsa_sign (const uint8_t blob, size_t blob_len, const uint8_t digestinfo, size_t di_len, uint8_t sig_out, size_t sig_cap, size_t sig_len_out)
	RSASSA-PKCS1-v1.5 signature over a host-supplied DigestInfo.
bool	gpg_rsa_selftest (uint16_t n_bits)
	End-to-end self-test: generate a key, serialise/reload its blob, then sign+verify and encrypt+decrypt a known sample. Exercises the full software RSA path on the running firmware (no SE / NVS).
bool	gpg_rsa_decrypt (const uint8_t blob, size_t blob_len, const uint8_t ct, size_t ct_len, uint8_t pt_out, size_t pt_cap, size_t pt_len_out)
	RSAES-PKCS1-v1.5 decryption of a cryptogram.

Variables
static const char *	TAG = "GPGRsa"
	Software RSA backend for the OpenPGP card (see rsa.h).

Function Documentation

◆ gpg_rsa_blob_build()

bool gpg_rsa_blob_build	(	uint16_t	n_bits,
		const uint8_t *	e,
		size_t	e_len,
		const uint8_t *	p,
		size_t	p_len,
		const uint8_t *	q,
		size_t	q_len,
		uint8_t *	blob_out,
		size_t	blob_cap,
		size_t *	blob_len_out )

Serialises raw RSA components into a private-key blob.

Parameters

n_bits	Modulus length in bits (2048 / 3072 / 4096).
e	Public exponent bytes (big-endian).
e_len	Public exponent length.
p	First prime (big-endian).
p_len	First prime length.
q	Second prime (big-endian).
q_len	Second prime length.
blob_out	Output buffer.
blob_cap	Output capacity.
blob_len_out	Receives the serialized length.

Returns: true when the components form a valid RSA private key.

Definition at line 110 of file rsa.cpp.

References LOG_W, rsa_serialize(), and TAG.

Referenced by cmd_put_data_odd().

◆ gpg_rsa_blob_public()

bool gpg_rsa_blob_public	(	const uint8_t *	blob,
		size_t	blob_len,
		uint8_t *	n_out,
		size_t	n_cap,
		size_t *	n_len_out,
		uint8_t *	e_out,
		size_t	e_cap,
		size_t *	e_len_out )

Extracts the public modulus and exponent from a private-key blob.

Parameters

blob	Serialized private-key blob.
blob_len	Blob length.
n_out	Receives the modulus (big-endian, n_bits/8 bytes).
n_cap	Capacity of n_out.
n_len_out	Receives the modulus length.
e_out	Receives the public exponent (big-endian).
e_cap	Capacity of e_out.
e_len_out	Receives the exponent length.

Returns: true on success.

Definition at line 156 of file rsa.cpp.

References rsa_load_ctx().

Referenced by build_rsa_pubkey_from_storage().

◆ gpg_rsa_decrypt()

bool gpg_rsa_decrypt	(	const uint8_t *	blob,
		size_t	blob_len,
		const uint8_t *	ct,
		size_t	ct_len,
		uint8_t *	pt_out,
		size_t	pt_cap,
		size_t *	pt_len_out )

RSAES-PKCS1-v1.5 decryption of a cryptogram.

Parameters

blob	Serialized private-key blob.
blob_len	Blob length.
ct	Ciphertext (exactly n_bits/8 bytes).
ct_len	Ciphertext length.
pt_out	Output plaintext buffer.
pt_cap	Capacity of pt_out.
pt_len_out	Receives the recovered plaintext length.

Returns: true on success.

Definition at line 267 of file rsa.cpp.

References LOG_W, rsa_load_ctx(), rsa_rng(), and TAG.

Referenced by cmd_pso_decipher(), and gpg_rsa_selftest().

◆ gpg_rsa_generate()

bool gpg_rsa_generate	(	uint16_t	n_bits,
		uint8_t *	blob_out,
		size_t	blob_cap,
		size_t *	blob_len_out )

Generates a fresh RSA key pair and serialises its private blob. The public exponent is fixed to 65537. This is computationally heavy on the ESP32-S3 (seconds to minutes for 4096); the caller is expected to keep the task watchdog fed.

Parameters

n_bits	Modulus length in bits (2048 / 3072 / 4096).
blob_out	Output buffer.
blob_cap	Output capacity.
blob_len_out	Receives the serialized length.

Returns: true on success.

Definition at line 138 of file rsa.cpp.

References LOG_E, rsa_rng(), rsa_serialize(), and TAG.

Referenced by cmd_generate_keypair(), and gpg_rsa_selftest().

◆ gpg_rsa_selftest()

bool gpg_rsa_selftest ( uint16_t n_bits )

End-to-end self-test: generate a key, serialise/reload its blob, then sign+verify and encrypt+decrypt a known sample. Exercises the full software RSA path on the running firmware (no SE / NVS).

Parameters

n_bits Modulus length to test (2048 / 3072 / 4096).

Returns: true if every step round-trips correctly.

Definition at line 208 of file rsa.cpp.

References gpg_rsa_decrypt(), gpg_rsa_generate(), GPG_RSA_MAX_MODULUS_BYTES, gpg_rsa_sign(), LOG_E, LOG_I, rsa_load_ctx(), rsa_rng(), and TAG.

Referenced by cdc::mod_gpg::cmd_gpg_rsa_selftest().

◆ gpg_rsa_sign()

bool gpg_rsa_sign	(	const uint8_t *	blob,
		size_t	blob_len,
		const uint8_t *	digestinfo,
		size_t	di_len,
		uint8_t *	sig_out,
		size_t	sig_cap,
		size_t *	sig_len_out )

RSASSA-PKCS1-v1.5 signature over a host-supplied DigestInfo.

GnuPG sends the full DER DigestInfo as the PSO:CDS / INTERNAL AUTHENTICATE payload; the card applies the EMSA-PKCS1-v1.5 padding and the raw RSA private operation.

Parameters

blob	Serialized private-key blob.
blob_len	Blob length.
digestinfo	DigestInfo bytes to sign.
di_len	DigestInfo length.
sig_out	Output signature buffer (>= n_bits/8 bytes).
sig_cap	Capacity of sig_out.
sig_len_out	Receives the signature length (= n_bits/8).

Returns: true on success.

Definition at line 185 of file rsa.cpp.

References LOG_W, rsa_load_ctx(), rsa_rng(), and TAG.

Referenced by cmd_internal_authenticate(), cmd_pso_cds(), and gpg_rsa_selftest().

◆ rd_u16()

bool rd_u16	(	const uint8_t *	b,
		size_t	len,
		size_t *	pos,
		uint16_t *	out )

static

Reads a big-endian u16 from a buffer and advances the cursor.

Definition at line 29 of file rsa.cpp.

Referenced by rsa_load_ctx().

◆ rsa_load_ctx()

bool rsa_load_ctx	(	const uint8_t *	blob,
		size_t	blob_len,
		mbedtls_rsa_context *	rsa )

static

Parses a private-key blob and imports it into an RSA context. On success the caller owns rsa and must free it.

Definition at line 40 of file rsa.cpp.

References rd_u16().

Referenced by gpg_rsa_blob_public(), gpg_rsa_decrypt(), gpg_rsa_selftest(), and gpg_rsa_sign().

◆ rsa_rng()

int rsa_rng	(	void *	ctx,
		unsigned char *	out,
		size_t	len )

static

mbedTLS RNG callback backed by the ESP hardware RNG.

Definition at line 20 of file rsa.cpp.

Referenced by gpg_rsa_decrypt(), gpg_rsa_generate(), gpg_rsa_selftest(), and gpg_rsa_sign().

◆ rsa_serialize()

bool rsa_serialize	(	mbedtls_rsa_context *	rsa,
		uint8_t *	out,
		size_t	cap,
		size_t *	out_len )

static

Canonically serialises an RSA context (primes + exponent) into a blob.

Definition at line 70 of file rsa.cpp.

Referenced by gpg_rsa_blob_build(), and gpg_rsa_generate().

Variable Documentation

◆ TAG

const char* TAG = "GPGRsa"

static

Software RSA backend for the OpenPGP card (see rsa.h).

Definition at line 15 of file rsa.cpp.

Functions

Variables

Function Documentation

◆ gpg_rsa_blob_build()

◆ gpg_rsa_blob_public()

◆ gpg_rsa_decrypt()

◆ gpg_rsa_generate()

◆ gpg_rsa_selftest()

◆ gpg_rsa_sign()

◆ rd_u16()

◆ rsa_load_ctx()

◆ rsa_rng()

◆ rsa_serialize()

Variable Documentation

◆ TAG