RSA-2048 PKCS#1 v1.5 signature primitive (RFC 8017) - verify + software sign. More...

#include <stddef.h>
#include <stdint.h>

Macros
#define	PC_RSA_KEY_BYTES 256
	RSA modulus / signature size in bytes (RSA-2048).

#define	PC_RSA_SIG_BYTES 256
	PKCS#1 v1.5 signature size for RSA-2048 in bytes.

#define	PC_PKCS1_DIGESTINFO_LEN 19
	Length of the DER DigestInfo wrapper for SHA-256 (RFC 8017 / RFC 5754).

#define	PC_PKCS1_SHA512_DIGESTINFO_LEN 19
	Length of the DER DigestInfo wrapper for SHA-512.

Enumerations
enum class	pc_rsa_hash : uint8_t { SHA256 = 0 , SHA512 = 1 }
	Hash algorithm selecting the RSA signature scheme (RFC 8017 §9.2). More...

Functions
int	pc_rsa_verify (const uint8_t n_be[PC_RSA_KEY_BYTES], const uint8_t e_be4[4], const uint8_t msg, size_t msg_len, const uint8_t sig, size_t sig_len, pc_rsa_hash hash)
	Verify an RSA-2048 PKCS#1 v1.5 signature over `msg`.

Variables
const uint8_t	pc_pkcs1_sha256_digestinfo [PC_PKCS1_DIGESTINFO_LEN]
	The DER-encoded DigestInfo wrapper for SHA-256 (prepend to the 32-byte digest).

const uint8_t	pc_pkcs1_sha512_digestinfo [PC_PKCS1_SHA512_DIGESTINFO_LEN]
	The DER-encoded DigestInfo wrapper for SHA-512 (prepend to the 64-byte digest).

Detailed Description

RSA-2048 PKCS#1 v1.5 signature primitive (RFC 8017) - verify + software sign.

The shared, protocol-agnostic RSA primitive: it takes raw big-endian key material (modulus n, exponent) and a message, and does the RSASSA-PKCS1-v1.5 math with a SHA-256 or SHA-512 digest. It knows nothing about SSH key blobs, host-key storage, or the "ssh-rsa" / "rsa-sha2-256" wire names - that layer lives in network_drivers/presentation/ssh/crypto/ssh_rsa and calls into this primitive.

Verify runs on both platforms (mbedtls on Arduino/ESP32, software on native). The software sign (pc_rsa_sign_sw, raw n/d) is the native-only reference path used by the tests; on-device signing with a cached host-key context is the SSH layer's job.

Author: Douglas Quigg (dstroy0)

Date: 2026

Definition in file rsa.h.

Macro Definition Documentation

◆ PC_RSA_KEY_BYTES

#define PC_RSA_KEY_BYTES 256

RSA modulus / signature size in bytes (RSA-2048).

Definition at line 28 of file rsa.h.

◆ PC_RSA_SIG_BYTES

#define PC_RSA_SIG_BYTES 256

PKCS#1 v1.5 signature size for RSA-2048 in bytes.

Definition at line 31 of file rsa.h.

◆ PC_PKCS1_DIGESTINFO_LEN

#define PC_PKCS1_DIGESTINFO_LEN 19

Length of the DER DigestInfo wrapper for SHA-256 (RFC 8017 / RFC 5754).

Definition at line 45 of file rsa.h.

◆ PC_PKCS1_SHA512_DIGESTINFO_LEN

#define PC_PKCS1_SHA512_DIGESTINFO_LEN 19

Length of the DER DigestInfo wrapper for SHA-512.

Definition at line 48 of file rsa.h.

Enumeration Type Documentation

◆ pc_rsa_hash

enum class pc_rsa_hash : uint8_t

strong

Hash algorithm selecting the RSA signature scheme (RFC 8017 §9.2).

Only the message hash and its DigestInfo OID differ between the two.

Enumerator
SHA256	RSASSA-PKCS1-v1.5 with SHA-256.
SHA512	RSASSA-PKCS1-v1.5 with SHA-512.

Definition at line 38 of file rsa.h.

Function Documentation

◆ pc_rsa_verify()

int pc_rsa_verify	(	const uint8_t	n_be[PC_RSA_KEY_BYTES],
		const uint8_t	e_be4[4],
		const uint8_t *	msg,
		size_t	msg_len,
		const uint8_t *	sig,
		size_t	sig_len,
		pc_rsa_hash	hash
	)

Verify an RSA-2048 PKCS#1 v1.5 signature over msg.

Parameters

n_be	Modulus n, 256 bytes big-endian.
e_be4	Public exponent e, 4 bytes big-endian (typically 65537).
msg	Message that was signed (this hashes it; do not pre-hash).
msg_len	Message length.
sig	Signature, big-endian.
sig_len	Signature length (must equal PC_RSA_KEY_BYTES).
hash	Digest algorithm (SHA-256 / SHA-512).

Returns: 0 if the signature is valid, -1 otherwise.

Definition at line 55 of file rsa.cpp.

References PC_RSA_KEY_BYTES, pc_sha256(), PC_SHA256_DIGEST_LEN, pc_sha512(), PC_SHA512_DIGEST_LEN, and SHA512.

Variable Documentation

◆ pc_pkcs1_sha256_digestinfo

const uint8_t pc_pkcs1_sha256_digestinfo[PC_PKCS1_DIGESTINFO_LEN]

extern

The DER-encoded DigestInfo wrapper for SHA-256 (prepend to the 32-byte digest).

Definition at line 31 of file rsa.cpp.

◆ pc_pkcs1_sha512_digestinfo

const uint8_t pc_pkcs1_sha512_digestinfo[PC_PKCS1_SHA512_DIGESTINFO_LEN]